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A 'B' entry's load program selects its interpreter by absolute path,
which open_exec() resolves at exec time in the mount namespace of whoever
runs the binary. The handler names an interpreter but does not get to say
which file that is. Whoever controls the filesystem view of the exec
decides that instead.
Static entries settled this long ago with 'F'. The interpreter is opened
at registration in the registrant's context and every exec runs a clone
of that file. Give a 'B' entry the same, for as many interpreters as it
needs.
An entry registered with 'D' cannot be matched yet, so it still belongs
to whoever is configuring it and can be given interpreters one write at a
time:
echo ':qemu:B::::qemu_user:D' > register
echo '+aarch64 /usr/bin/qemu-aarch64' > qemu
echo '+arm /usr/bin/qemu-arm' > qemu
echo 1 > qemu
Each path is opened by its write, with the credentials the entry file
was opened with, by the same helper that opens an 'F' interpreter. The
load program picks one per exec with bpf_binprm_select_interp() and the
entry hands out a clone of it. Nothing is resolved again, in any
namespace. The path is everything past the first space, so no
interpreter has to fit in a register string. An entry binds at most a
hundred interpreters (BINFMT_MISC_INTERP_MAX). Every binding pins a
struct file that no file descriptor accounts for, so RLIMIT_NOFILE does
not apply and some cap is needed. A hundred is plenty and raising it
later is cheap, lowering it is not.
Selection is by name so the register string and the program need not
agree on an order, and so the handler is not tied to where a distribution
puts its interpreters. A name is a single word of printable ASCII so the
entry file can report 'name path' lines. The interpreter runs under the
path it was registered under.
The entry file reads user memory once. bm_entry_write() copies the write
in and dispatches on the first byte, and parse_command() takes the copied
buffer. The status file has no binding to spell, so it keeps its own
small copy in read_command().
That moves the length cap ahead of the dispatch. A write to an entry file
longer than a binding can be is now refused with -E2BIG, and one from a
bad address reports -EFAULT, where the command parser used to report
-EINVAL for anything past three bytes.
Configurations of one instance are kept apart by the lock removal
already takes. Reading the set out of the entry file takes no lock.
Bindings are rcu-published and the open entry file pins the entry
together with everything it bound, so a reader either sees a whole node
or misses it. The interpreter is opened before the configuration lock
because resolving the path may walk this very filesystem, and only
after the command has been parsed and the name validated from the
copied buffer, so a write that can never bind opens nothing and the
errno reflects the actual failure.
Link: https://patch.msgid.link/20260730-work-binfmt_misc-preopen-v1-7-4a0b0da71f16@kernel.org
Signed-off-by: Christian Brauner (Amutable) <brauner@kernel.org>
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binfmt_misc currently supports an execution model where the registered
interpreter becomes the executed program and the matched binary is
handed to it as payload. The upcoming binfmt_misc loader mode inverts
this. The matched binary remains the executed program and the registered
interpreter is substituted into the role the binary's PT_INTERP would
have played.
Add the channel for that hand-over. bprm->loader carries an
open_exec-style struct file reference from the binfmt_misc match to the
binary format that consumes it. Unlike bprm->interpreter it does not
request a restart of the format search. The stashing handler declines
the exec with -ENOEXEC and the search continues to the real format in
the same round.
Both ELF loaders consume it, so give them the two helpers to do it with
rather than a copy each. bprm_open_interpreter() hands out the substitute
in place of what PT_INTERP names and bprm_drop_loader() releases one that
turned out not to apply.
Establish the complete lifecycle up front so a stashed loader can
neither leak nor be silently ignored.
- Chain restart: if another format wins the round by staging
bprm->interpreter (binfmt_script) the stashed loader belonged to
the file being replaced. Drop it at the top of the swap block in
exec_binprm().
- Unclaimed or error: free_bprm() releases a still-stashed loader
next to the other bprm file references.
- Silent non-substitution: a final format that reaches
begin_new_exec() with a pending loader would run the binary while
ignoring the override. Refuse with -ENOEXEC before the point of no
return. Formats that do not know about the override (binfmt_flat,
out-of-tree) need no changes.
Link: https://patch.msgid.link/20260721-work-bpf-binfmt_misc-ptinterp-v2-15-e57866e4ae0f@kernel.org
Signed-off-by: Christian Brauner (Amutable) <brauner@kernel.org>
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A transparent binfmt_misc dispatch hands the binary to the interpreter
through AT_EXECFD and leaves the argument vector exactly as the caller
built it. The loader on the receiving end has to know which contract it
got.
On the classic 'O'/'C' entries the binary's path is spliced into the
argument vector and the loader consumes arguments. In transparent mode
nothing was spliced and argv belongs entirely to the program. This
cannot be inferred from AT_EXECFD alone. Raise a new AT_FLAGS bit
following the AT_FLAGS_PRESERVE_ARGV0 precedent added for qemu-user in
commit 2347961b11d4 ("binfmt_misc: pass binfmt_misc flags to the
interpreter").
The bit also announces that mm->exe_file names the binary rather than
the interpreter (added in the next commit). A loader that sees the bit
may finish the identity polish by fixing up AT_PHDR/AT_ENTRY/AT_BASE in
saved_auxv and fix the code/data markers via one uncapped PR_SET_MM_MAP
once it has mapped the binary. I've got glibc patches for this as well
but it's useful for any loader.
BINPRM_FLAGS_TRANSPARENT_INTERP carries the mode from binfmt_misc to the
ELF loaders. Both had their own copy of the AT_FLAGS translation, so
give them one bprm_at_flags() to share instead of a second copy that can
drift. Nothing sets the bprm flag yet.
Link: https://patch.msgid.link/20260721-work-bpf-binfmt_misc-ptinterp-v2-8-e57866e4ae0f@kernel.org
Signed-off-by: Christian Brauner (Amutable) <brauner@kernel.org>
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The upcoming bpf-backed binfmt_misc handlers decide how a binary is run
programmatically at exec time: the interpreter itself, an optional
single argument to pass to it, and the invocation flags that a static
binfmt_misc entry fixes at registration time. The selection runs before
load_misc_binary() has copied the binary path from bprm->interp into
the argument vector, so the selecting program cannot go through
bprm_change_interp() directly without clobbering argv[1].
Stage the selected state in the bprm instead, grouped in struct
binfmt_misc_bpf and embedded anonymously in struct linux_binprm so the
bprm->bpf_* accesses stay direct. The bprm is exclusively owned by the
task doing the exec so no synchronization is needed. The consumers
free and clear the fields once the exec attempt that set them is
finished; free_bprm() covers all error paths.
Link: https://patch.msgid.link/20260714-work-bpf-binfmt_misc-v2-1-57b7529c002c@kernel.org
Reviewed-by: Farid Zakaria <farid.m.zakaria@gmail.com>
Signed-off-by: Christian Brauner (Amutable) <brauner@kernel.org>
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Once binfmt_misc is loaded load_misc_binary() runs for every execve()
on the system since binfmt_misc registers at the head of the formats
list. Every exec therefore performs read_lock() and read_unlock() on
the entries_lock of the relevant binfmt_misc instance, i.e., two
atomic read-modify-writes on a shared cacheline. User namespaces
without their own binfmt_misc mount fall back to an ancestor's
instance so on container-heavy systems every exec on the machine
typically ends up hammering the cacheline of init_binfmt_misc. On
PREEMPT_RT the rwlock additionally turns the handler lookup into a
sleeping lock on the exec fast path.
The lock protects very little. Entries are immutable after publication
except for the Enabled bit which is already toggled locklessly via
set_bit()/clear_bit() and entry lifetime is already handled by the
users refcount via get_binfmt_handler()/put_binfmt_handler(). The read
lock's only remaining job is to make "the entry is still linked" and
"take a reference" atomic with respect to the unlink sites.
Switch the lookup to an RCU walk:
* Lookup walks the entry list under rcu_read_lock() and acquires a
reference via refcount_inc_not_zero(). The refcount can only drop to
zero after an entry has been unlinked so a failed increment means
the walk raced with an unlink. Restarting the search is bounded
because an unlinked entry cannot be found again.
* The unlink sites use hlist_del_init_rcu() which keeps the forward
pointer intact for concurrent walkers and preserves hlist_unhashed()
as the protection against double removal.
* The final put frees the entry via kfree_rcu() as a concurrent walker
may still dereference its flags, magic, mask, and inline strings.
They all live in the entry allocation itself and thus stay valid
until a grace period has elapsed. Closing the interpreter file stays
synchronous. It is only used with a reference already held and all
final puts run in process context.
* Writers remain serialized by the inode lock of the root dentry with
one exception. bm_evict_inode() called from generic_shutdown_super()
during umount unlinks entries without holding it. Keep a spinlock
around the unlink sites instead of relying on superblock lifetime
rules to make that exclusion implicit.
Handler removal semantics are unchanged. An exec that acquired a
reference just before its handler was unregistered already completes
with the removed handler today. The read lock never protected against
that, it only made the window smaller.
With this an exec that matches no binfmt_misc entry, the common case,
no longer writes to any shared cacheline at all.
Link: https://patch.msgid.link/20260710-work-binfmt_misc-locking-v3-5-a162f7cb58d6@kernel.org
Reviewed-by: Jori Koolstra <jkoolstra@xs4all.nl>
Signed-off-by: Christian Brauner (Amutable) <brauner@kernel.org>
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The upcoming conversion of the handler lookup to RCU walks cannot use
list_del_init(): reinitializing the forward pointer of a removed entry
would make a concurrent lockless walker standing on that entry loop
back onto it indefinitely. The removal paths do rely on
reinitialization though because bm_{entry,status}_write() and
bm_evict_inode() need to detect whether an entry has already been
unlinked.
hlists support exactly this pattern: hlist_del_init_rcu() keeps the
forward pointer of the removed entry intact for concurrent walkers and
only zeroes ->pprev with hlist_unhashed() serving as the linked test.
Convert the entry list to an hlist now while keeping the rwlock so the
subsequent RCU conversion is a pure locking change. hlist_add_head()
inserts at the head just as list_add() did so lookup precedence
between registered handlers is unchanged.
Link: https://patch.msgid.link/20260710-work-binfmt_misc-locking-v3-4-a162f7cb58d6@kernel.org
Reviewed-by: Jori Koolstra <jkoolstra@xs4all.nl>
Signed-off-by: Christian Brauner (Amutable) <brauner@kernel.org>
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exec_mmap() installs the new mm and then tears the old one down while
still holding exec_update_lock for writing -- and with cred_guard_mutex
held all the way to setup_new_exec():
setmax_mm_hiwater_rss(&tsk->signal->maxrss, old_mm);
mm_update_next_owner(old_mm);
mmput(old_mm);
Neither lock is needed for this. exec_update_lock only exists to make the
mm swap atomic with the later commit_creds(), so that permission-checking
readers (proc, ptrace, the futex robust list, perf, kcmp, mm_access())
never observe the new mm together with the old credentials. Those readers
all operate on task->mm, i.e. the new mm after the swap; none looks at the
detached old mm, its ->owner or signal->maxrss. cred_guard_mutex guards
credential calculation and is equally irrelevant here.
The cost is real: __mmput() runs exit_mmap() over the entire old address
space and can block in exit_aio() waiting for in-flight AIO, all while
holding exec_update_lock for writing and cred_guard_mutex. For execve() of
a large process this blocks ptrace_attach() and every exec_update_lock
reader for the duration of the teardown.
Stash the old mm in bprm->old_mm and release it from setup_new_exec()
after both locks are dropped. setup_new_exec() still runs before
setup_arg_pages() and the segment mappings, so the old address space is
freed before the new one is populated and peak memory is unchanged. The
ordering constraints are kept: old_mm's mmap_lock is still dropped in
exec_mmap() before mm_update_next_owner() (required since commit
31a78f23bac0 ("mm owner: fix race between swapoff and exit")), and
mm_update_next_owner() still precedes mmput(); both run in the execing
task's context, as mm_update_next_owner() requires.
If exec swaps the mm but fails before setup_new_exec() runs the old mm
would leak, so add a backstop in free_bprm(). The lazy-tlb case
(old_mm == NULL, e.g. kernel_execve()) has no address space to
free and is left in exec_mmap().
Link: https://patch.msgid.link/20260522-work-exit_mm-v1-1-bd32d5a560bb@kernel.org
Signed-off-by: Christian Brauner (Amutable) <brauner@kernel.org>
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The dumpable flag captured at execve() is consulted by
__ptrace_may_access() and several /proc owner / visibility checks.
It lives on mm_struct today, which exit_mm() clears from the task
long before the task itself is reaped.
exec_state is anchored to the execve() that established the current
privilege domain. CLONE_VM siblings refcount-share the parent's
exec_state via copy_exec_state(); non-CLONE_VM clones allocate a
fresh exec_state inheriting the parent's dumpable mode and user_ns
reference via task_exec_state_copy(). execve() allocates a fresh
instance (via alloc_task_exec_state() in begin_new_exec()) and
installs it under task_lock + exec_update_lock with
task_exec_state_replace(). init_task uses a static instance.
The dumpable mode now lives on task->exec_state->dumpable.
task->mm->flags no longer carries dumpability; MMF_DUMPABLE_MASK is
removed, but MMF_DUMPABLE_BITS is reserved so MMF_DUMP_FILTER_* bit
positions remain stable for the /proc/<pid>/coredump_filter ABI. The
task->user_dumpable cache bit and its assignment in exit_mm() are
removed; readers go through get_dumpable(task) directly.
coredump_params gains a snapshot field cprm.dumpable, populated from
get_dumpable(current) at vfs_coredump() entry, replacing the previous
__get_dumpable(cprm->mm_flags) consumers in fs/coredump.c and
fs/pidfs.c.
The user namespace recorded at execve() is consulted by
__ptrace_may_access() and by /proc/PID/* owner derivation. Move the
captured user_ns onto task_exec_state, which stays attached to the task
past exit_mm() and across exit_files().
bprm grows a user_ns field staged in bprm_mm_init() with the caller's
user_ns, narrowed by would_dump() to the closest privileged ancestor,
and consumed by exec_mmap() via alloc_task_exec_state(bprm->user_ns).
free_bprm() releases the staging reference.
mm_struct loses ->user_ns entirely. Initializers in init-mm, efi_mm,
and the implicit one in mm_init()/dup_mm()/mm_alloc() are removed;
__mmdrop() drops the matching put_user_ns(). The kthread_use_mm()
WARN_ON_ONCE(!mm->user_ns) is no longer meaningful and goes too.
Reviewed-by: Jann Horn <jannh@google.com>
Link: https://patch.msgid.link/20260520-work-task_exec_state-v3-4-69f895bc1385@kernel.org
Signed-off-by: Christian Brauner (Amutable) <brauner@kernel.org>
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This system call has been deprecated for quite a while now.
Let's try and remove it from the kernel completely.
Link: https://lore.kernel.org/20250415-kanufahren-besten-02ac00e6becd@brauner
Acked-by: Kees Cook <kees@kernel.org>
Signed-off-by: Christian Brauner <brauner@kernel.org>
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Commit 987f20a9dcce ("a.out: Remove the a.out implementation") removed
the last in-tree user of the loader field, and as far as I can tell, it
was the only one historically.
Signed-off-by: Yonatan Goldschmidt <yon.goldschmidt@gmail.com>
Link: https://lore.kernel.org/r/20250223223234.13764-1-yon.goldschmidt@gmail.com
Signed-off-by: Kees Cook <kees@kernel.org>
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git://git.kernel.org/pub/scm/linux/kernel/git/kees/linux
Pull AT_EXECVE_CHECK from Kees Cook:
- Implement AT_EXECVE_CHECK flag to execveat(2) (Mickaël Salaün)
- Implement EXEC_RESTRICT_FILE and EXEC_DENY_INTERACTIVE securebits
(Mickaël Salaün)
- Add selftests and samples for AT_EXECVE_CHECK (Mickaël Salaün)
* tag 'AT_EXECVE_CHECK-v6.14-rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/kees/linux:
ima: instantiate the bprm_creds_for_exec() hook
samples/check-exec: Add an enlighten "inc" interpreter and 28 tests
selftests: ktap_helpers: Fix uninitialized variable
samples/check-exec: Add set-exec
selftests/landlock: Add tests for execveat + AT_EXECVE_CHECK
selftests/exec: Add 32 tests for AT_EXECVE_CHECK and exec securebits
security: Add EXEC_RESTRICT_FILE and EXEC_DENY_INTERACTIVE securebits
exec: Add a new AT_EXECVE_CHECK flag to execveat(2)
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Add a new AT_EXECVE_CHECK flag to execveat(2) to check if a file would
be allowed for execution. The main use case is for script interpreters
and dynamic linkers to check execution permission according to the
kernel's security policy. Another use case is to add context to access
logs e.g., which script (instead of interpreter) accessed a file. As
any executable code, scripts could also use this check [1].
This is different from faccessat(2) + X_OK which only checks a subset of
access rights (i.e. inode permission and mount options for regular
files), but not the full context (e.g. all LSM access checks). The main
use case for access(2) is for SUID processes to (partially) check access
on behalf of their caller. The main use case for execveat(2) +
AT_EXECVE_CHECK is to check if a script execution would be allowed,
according to all the different restrictions in place. Because the use
of AT_EXECVE_CHECK follows the exact kernel semantic as for a real
execution, user space gets the same error codes.
An interesting point of using execveat(2) instead of openat2(2) is that
it decouples the check from the enforcement. Indeed, the security check
can be logged (e.g. with audit) without blocking an execution
environment not yet ready to enforce a strict security policy.
LSMs can control or log execution requests with
security_bprm_creds_for_exec(). However, to enforce a consistent and
complete access control (e.g. on binary's dependencies) LSMs should
restrict file executability, or measure executed files, with
security_file_open() by checking file->f_flags & __FMODE_EXEC.
Because AT_EXECVE_CHECK is dedicated to user space interpreters, it
doesn't make sense for the kernel to parse the checked files, look for
interpreters known to the kernel (e.g. ELF, shebang), and return ENOEXEC
if the format is unknown. Because of that, security_bprm_check() is
never called when AT_EXECVE_CHECK is used.
It should be noted that script interpreters cannot directly use
execveat(2) (without this new AT_EXECVE_CHECK flag) because this could
lead to unexpected behaviors e.g., `python script.sh` could lead to Bash
being executed to interpret the script. Unlike the kernel, script
interpreters may just interpret the shebang as a simple comment, which
should not change for backward compatibility reasons.
Because scripts or libraries files might not currently have the
executable permission set, or because we might want specific users to be
allowed to run arbitrary scripts, the following patch provides a dynamic
configuration mechanism with the SECBIT_EXEC_RESTRICT_FILE and
SECBIT_EXEC_DENY_INTERACTIVE securebits.
This is a redesign of the CLIP OS 4's O_MAYEXEC:
https://github.com/clipos-archive/src_platform_clip-patches/blob/f5cb330d6b684752e403b4e41b39f7004d88e561/1901_open_mayexec.patch
This patch has been used for more than a decade with customized script
interpreters. Some examples can be found here:
https://github.com/clipos-archive/clipos4_portage-overlay/search?q=O_MAYEXEC
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Christian Brauner <brauner@kernel.org>
Cc: Kees Cook <keescook@chromium.org>
Acked-by: Paul Moore <paul@paul-moore.com>
Reviewed-by: Serge Hallyn <serge@hallyn.com>
Reviewed-by: Jeff Xu <jeffxu@chromium.org>
Tested-by: Jeff Xu <jeffxu@chromium.org>
Link: https://docs.python.org/3/library/io.html#io.open_code [1]
Signed-off-by: Mickaël Salaün <mic@digikod.net>
Link: https://lore.kernel.org/r/20241212174223.389435-2-mic@digikod.net
Signed-off-by: Kees Cook <kees@kernel.org>
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Zbigniew mentioned at Linux Plumber's that systemd is interested in
switching to execveat() for service execution, but can't, because the
contents of /proc/pid/comm are the file descriptor which was used,
instead of the path to the binary[1]. This makes the output of tools like
top and ps useless, especially in a world where most fds are opened
CLOEXEC so the number is truly meaningless.
When the filename passed in is empty (e.g. with AT_EMPTY_PATH), use the
dentry's filename for "comm" instead of using the useless numeral from
the synthetic fdpath construction. This way the actual exec machinery
is unchanged, but cosmetically the comm looks reasonable to admins
investigating things.
Instead of adding TASK_COMM_LEN more bytes to bprm, use one of the unused
flag bits to indicate that we need to set "comm" from the dentry.
Suggested-by: Zbigniew Jędrzejewski-Szmek <zbyszek@in.waw.pl>
Suggested-by: Tycho Andersen <tandersen@netflix.com>
Suggested-by: Al Viro <viro@zeniv.linux.org.uk>
Suggested-by: Linus Torvalds <torvalds@linux-foundation.org>
Link: https://github.com/uapi-group/kernel-features#set-comm-field-before-exec [1]
Reviewed-by: Aleksa Sarai <cyphar@cyphar.com>
Tested-by: Zbigniew Jędrzejewski-Szmek <zbyszek@in.waw.pl>
Signed-off-by: Kees Cook <kees@kernel.org>
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When argmin was added in commit 655c16a8ce9c ("exec: separate
MM_ANONPAGES and RLIMIT_STACK accounting"), it was intended only for
validating stack limits on CONFIG_MMU[1]. All checking for reaching the
limit (argmin) is wrapped in CONFIG_MMU ifdef checks, though setting
argmin was not. That argmin is only supposed to be used under CONFIG_MMU
was rediscovered recently[2], and I don't want to trip over this again.
Move argmin's declaration into the existing CONFIG_MMU area, and add
helpers functions so the MMU tests can be consolidated.
Link: https://lore.kernel.org/all/20181126122307.GA1660@redhat.com [1]
Link: https://lore.kernel.org/all/202406211253.7037F69@keescook/ [2]
Link: https://lore.kernel.org/r/20240621205046.4001362-1-kees@kernel.org
Signed-off-by: Kees Cook <kees@kernel.org>
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Enable unprivileged sandboxes to create their own binfmt_misc mounts.
This is based on Laurent's work in [1] but has been significantly
reworked to fix various issues we identified in earlier versions.
While binfmt_misc can currently only be mounted in the initial user
namespace, binary types registered in this binfmt_misc instance are
available to all sandboxes (Either by having them installed in the
sandbox or by registering the binary type with the F flag causing the
interpreter to be opened right away). So binfmt_misc binary types are
already delegated to sandboxes implicitly.
However, while a sandbox has access to all registered binary types in
binfmt_misc a sandbox cannot currently register its own binary types
in binfmt_misc. This has prevented various use-cases some of which were
already outlined in [1] but we have a range of issues associated with
this (cf. [3]-[5] below which are just a small sample).
Extend binfmt_misc to be mountable in non-initial user namespaces.
Similar to other filesystem such as nfsd, mqueue, and sunrpc we use
keyed superblock management. The key determines whether we need to
create a new superblock or can reuse an already existing one. We use the
user namespace of the mount as key. This means a new binfmt_misc
superblock is created once per user namespace creation. Subsequent
mounts of binfmt_misc in the same user namespace will mount the same
binfmt_misc instance. We explicitly do not create a new binfmt_misc
superblock on every binfmt_misc mount as the semantics for
load_misc_binary() line up with the keying model. This also allows us to
retrieve the relevant binfmt_misc instance based on the caller's user
namespace which can be done in a simple (bounded to 32 levels) loop.
Similar to the current binfmt_misc semantics allowing access to the
binary types in the initial binfmt_misc instance we do allow sandboxes
access to their parent's binfmt_misc mounts if they do not have created
a separate binfmt_misc instance.
Overall, this will unblock the use-cases mentioned below and in general
will also allow to support and harden execution of another
architecture's binaries in tight sandboxes. For instance, using the
unshare binary it possible to start a chroot of another architecture and
configure the binfmt_misc interpreter without being root to run the
binaries in this chroot and without requiring the host to modify its
binary type handlers.
Henning had already posted a few experiments in the cover letter at [1].
But here's an additional example where an unprivileged container
registers qemu-user-static binary handlers for various binary types in
its separate binfmt_misc mount and is then seamlessly able to start
containers with a different architecture without affecting the host:
root [lxc monitor] /var/snap/lxd/common/lxd/containers f1
1000000 \_ /sbin/init
1000000 \_ /lib/systemd/systemd-journald
1000000 \_ /lib/systemd/systemd-udevd
1000100 \_ /lib/systemd/systemd-networkd
1000101 \_ /lib/systemd/systemd-resolved
1000000 \_ /usr/sbin/cron -f
1000103 \_ /usr/bin/dbus-daemon --system --address=systemd: --nofork --nopidfile --systemd-activation --syslog-only
1000000 \_ /usr/bin/python3 /usr/bin/networkd-dispatcher --run-startup-triggers
1000104 \_ /usr/sbin/rsyslogd -n -iNONE
1000000 \_ /lib/systemd/systemd-logind
1000000 \_ /sbin/agetty -o -p -- \u --noclear --keep-baud console 115200,38400,9600 vt220
1000107 \_ dnsmasq --conf-file=/dev/null -u lxc-dnsmasq --strict-order --bind-interfaces --pid-file=/run/lxc/dnsmasq.pid --liste
1000000 \_ [lxc monitor] /var/lib/lxc f1-s390x
1100000 \_ /usr/bin/qemu-s390x-static /sbin/init
1100000 \_ /usr/bin/qemu-s390x-static /lib/systemd/systemd-journald
1100000 \_ /usr/bin/qemu-s390x-static /usr/sbin/cron -f
1100103 \_ /usr/bin/qemu-s390x-static /usr/bin/dbus-daemon --system --address=systemd: --nofork --nopidfile --systemd-ac
1100000 \_ /usr/bin/qemu-s390x-static /usr/bin/python3 /usr/bin/networkd-dispatcher --run-startup-triggers
1100104 \_ /usr/bin/qemu-s390x-static /usr/sbin/rsyslogd -n -iNONE
1100000 \_ /usr/bin/qemu-s390x-static /lib/systemd/systemd-logind
1100000 \_ /usr/bin/qemu-s390x-static /sbin/agetty -o -p -- \u --noclear --keep-baud console 115200,38400,9600 vt220
1100000 \_ /usr/bin/qemu-s390x-static /sbin/agetty -o -p -- \u --noclear --keep-baud pts/0 115200,38400,9600 vt220
1100000 \_ /usr/bin/qemu-s390x-static /sbin/agetty -o -p -- \u --noclear --keep-baud pts/1 115200,38400,9600 vt220
1100000 \_ /usr/bin/qemu-s390x-static /sbin/agetty -o -p -- \u --noclear --keep-baud pts/2 115200,38400,9600 vt220
1100000 \_ /usr/bin/qemu-s390x-static /sbin/agetty -o -p -- \u --noclear --keep-baud pts/3 115200,38400,9600 vt220
1100000 \_ /usr/bin/qemu-s390x-static /lib/systemd/systemd-udevd
[1]: https://lore.kernel.org/all/20191216091220.465626-1-laurent@vivier.eu
[2]: https://discuss.linuxcontainers.org/t/binfmt-misc-permission-denied
[3]: https://discuss.linuxcontainers.org/t/lxd-binfmt-support-for-qemu-static-interpreters
[4]: https://discuss.linuxcontainers.org/t/3-1-0-binfmt-support-service-in-unprivileged-guest-requires-write-access-on-hosts-proc-sys-fs-binfmt-misc
[5]: https://discuss.linuxcontainers.org/t/qemu-user-static-not-working-4-11
Link: https://lore.kernel.org/r/20191216091220.465626-2-laurent@vivier.eu (origin)
Link: https://lore.kernel.org/r/20211028103114.2849140-2-brauner@kernel.org (v1)
Cc: Sargun Dhillon <sargun@sargun.me>
Cc: Serge Hallyn <serge@hallyn.com>
Cc: Jann Horn <jannh@google.com>
Cc: Henning Schild <henning.schild@siemens.com>
Cc: Andrei Vagin <avagin@gmail.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Laurent Vivier <laurent@vivier.eu>
Cc: linux-fsdevel@vger.kernel.org
Signed-off-by: Laurent Vivier <laurent@vivier.eu>
Signed-off-by: Christian Brauner <christian.brauner@ubuntu.com>
Signed-off-by: Christian Brauner <brauner@kernel.org>
Signed-off-by: Kees Cook <keescook@chromium.org>
---
/* v2 */
- Serge Hallyn <serge@hallyn.com>:
- Use GFP_KERNEL_ACCOUNT for userspace triggered allocations when a
new binary type handler is registered.
- Christian Brauner <christian.brauner@ubuntu.com>:
- Switch authorship to me. I refused to do that earlier even though
Laurent said I should do so because I think it's genuinely bad form.
But by now I have changed so many things that it'd be unfair to
blame Laurent for any potential bugs in here.
- Add more comments that explain what's going on.
- Rename functions while changing them to better reflect what they are
doing to make the code easier to understand.
- In the first version when a specific binary type handler was removed
either through a write to the entry's file or all binary type
handlers were removed by a write to the binfmt_misc mount's status
file all cleanup work happened during inode eviction.
That includes removal of the relevant entries from entry list. While
that works fine I disliked that model after thinking about it for a
bit. Because it means that there was a window were someone has
already removed a or all binary handlers but they could still be
safely reached from load_misc_binary() when it has managed to take
the read_lock() on the entries list while inode eviction was already
happening. Again, that perfectly benign but it's cleaner to remove
the binary handler from the list immediately meaning that ones the
write to then entry's file or the binfmt_misc status file returns
the binary type cannot be executed anymore. That gives stronger
guarantees to the user.
|
|
With commit 987f20a9dcce ("a.out: Remove the a.out implementation"), the
use of the special taso flag for alpha architectures in the linux_binprm
struct is gone.
Remove the definition of taso in the linux_binprm struct.
No functional change.
Signed-off-by: Lukas Bulwahn <lukas.bulwahn@gmail.com>
Reviewed-by: "Eric W. Biederman" <ebiederm@xmission.com>
Signed-off-by: Kees Cook <keescook@chromium.org>
Link: https://lore.kernel.org/r/20220929203903.9475-1-lukas.bulwahn@gmail.com
|
|
Move the definition of struct coredump_params into coredump.h where
it belongs.
Remove the slightly errorneous comment explaining why struct
coredump_params was declared in binfmts.h.
Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>
|
|
struct linux_binfmt::core_dump and struct min_coredump::min_coredump
are used under CONFIG_COREDUMP only. Shrink those embedded configs
a bit.
Signed-off-by: Alexey Dobriyan <adobriyan@gmail.com>
Signed-off-by: Kees Cook <keescook@chromium.org>
Link: https://lore.kernel.org/r/YglbIFyN+OtwVyjW@localhost.localdomain
|
|
have dump_skip() just remember how much needs to be skipped,
leave actual seeks/writing zeroes to the next dump_emit()
or the end of coredump output, whichever comes first.
And instead of playing with do_truncate() in the end, just
write one NUL at the end of the last gap (if any).
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
|
|
It can be useful to the interpreter to know which flags are in use.
For instance, knowing if the preserve-argv[0] is in use would
allow to skip the pathname argument.
This patch uses an unused auxiliary vector, AT_FLAGS, to add a
flag to inform interpreter if the preserve-argv[0] is enabled.
Note by Helge Deller:
The real-world user of this patch is qemu-user, which needs to know
if it has to preserve the argv[0]. See Debian bug #970460.
Signed-off-by: Laurent Vivier <laurent@vivier.eu>
Reviewed-by: YunQiang Su <ysu@wavecomp.com>
URL: http://bugs.debian.org/970460
Signed-off-by: Helge Deller <deller@gmx.de>
|
|
To allow the kernel not to play games with set_fs to call exec
implement kernel_execve. The function kernel_execve takes pointers
into kernel memory and copies the values pointed to onto the new
userspace stack.
The calls with arguments from kernel space of do_execve are replaced
with calls to kernel_execve.
The calls do_execve and do_execveat are made static as there are now
no callers outside of exec.
The comments that mention do_execve are updated to refer to
kernel_execve or execve depending on the circumstances. In addition
to correcting the comments, this makes it easy to grep for do_execve
and verify it is not used.
Inspired-by: https://lkml.kernel.org/r/20200627072704.2447163-1-hch@lst.de
Reviewed-by: Kees Cook <keescook@chromium.org>
Link: https://lkml.kernel.org/r/87wo365ikj.fsf@x220.int.ebiederm.org
Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>
|
|
Currently it is necessary for the usermode helper code and the code
that launches init to use set_fs so that pages coming from the kernel
look like they are coming from userspace.
To allow that usage of set_fs to be removed cleanly the argument
copying from userspace needs to happen earlier. Move the computation
of bprm->filename and possible allocation of a name in the case
of execveat into alloc_bprm to make that possible.
The exectuable name, the arguments, and the environment are
copied into the new usermode stack which is stored in bprm
until exec passes the point of no return.
As the executable name is copied first onto the usermode stack
it needs to be known. As there are no dependencies to computing
the executable name, compute it early in alloc_bprm.
As an implementation detail if the filename needs to be generated
because it embeds a file descriptor store that filename in a new field
bprm->fdpath, and free it in free_bprm. Previously this was done in
an independent variable pathbuf. I have renamed pathbuf fdpath
because fdpath is more suggestive of what kind of path is in the
variable. I moved fdpath into struct linux_binprm because it is
tightly tied to the other variables in struct linux_binprm, and as
such is needed to allow the call alloc_binprm to move.
Reviewed-by: Kees Cook <keescook@chromium.org>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Link: https://lkml.kernel.org/r/87k0z66x8f.fsf@x220.int.ebiederm.org
Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>
|
|
The general convention in the linux kernel is to define a pointer
member as "type *name". The declaration of struct linux_binprm has
several pointer defined as "type * name". Update them to the
form of "type *name" for consistency.
Suggested-by: Kees Cook <keescook@chromium.org>
Reviewed-by: Kees Cook <keescook@chromium.org>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Link: https://lkml.kernel.org/r/87v9iq6x9x.fsf@x220.int.ebiederm.org
Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>
|
|
Now that the last callser has been removed remove this code from exec.
For anyone thinking of resurrecing do_execve_file please note that
the code was buggy in several fundamental ways.
- It did not ensure the file it was passed was read-only and that
deny_write_access had been called on it. Which subtlely breaks
invaniants in exec.
- The caller of do_execve_file was expected to hold and put a
reference to the file, but an extra reference for use by exec was
not taken so that when exec put it's reference to the file an
underflow occured on the file reference count.
- The point of the interface was so that a pathname did not need to
exist. Which breaks pathname based LSMs.
Tetsuo Handa originally reported these issues[1]. While it was clear
that deny_write_access was missing the fundamental incompatibility
with the passed in O_RDWR filehandle was not immediately recognized.
All of these issues were fixed by modifying the usermode driver code
to have a path, so it did not need this hack.
Reported-by: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
[1] https://lore.kernel.org/linux-fsdevel/2a8775b4-1dd5-9d5c-aa42-9872445e0942@i-love.sakura.ne.jp/
v1: https://lkml.kernel.org/r/871rm2f0hi.fsf_-_@x220.int.ebiederm.org
v2: https://lkml.kernel.org/r/87lfk54p0m.fsf_-_@x220.int.ebiederm.org
Link: https://lkml.kernel.org/r/20200702164140.4468-10-ebiederm@xmission.com
Reviewed-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Acked-by: Alexei Starovoitov <ast@kernel.org>
Tested-by: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>
|
|
Merge yet more updates from Andrew Morton:
- More MM work. 100ish more to go. Mike Rapoport's "mm: remove
__ARCH_HAS_5LEVEL_HACK" series should fix the current ppc issue
- Various other little subsystems
* emailed patches from Andrew Morton <akpm@linux-foundation.org>: (127 commits)
lib/ubsan.c: fix gcc-10 warnings
tools/testing/selftests/vm: remove duplicate headers
selftests: vm: pkeys: fix multilib builds for x86
selftests: vm: pkeys: use the correct page size on powerpc
selftests/vm/pkeys: override access right definitions on powerpc
selftests/vm/pkeys: test correct behaviour of pkey-0
selftests/vm/pkeys: introduce a sub-page allocator
selftests/vm/pkeys: detect write violation on a mapped access-denied-key page
selftests/vm/pkeys: associate key on a mapped page and detect write violation
selftests/vm/pkeys: associate key on a mapped page and detect access violation
selftests/vm/pkeys: improve checks to determine pkey support
selftests/vm/pkeys: fix assertion in test_pkey_alloc_exhaust()
selftests/vm/pkeys: fix number of reserved powerpc pkeys
selftests/vm/pkeys: introduce powerpc support
selftests/vm/pkeys: introduce generic pkey abstractions
selftests: vm: pkeys: use the correct huge page size
selftests/vm/pkeys: fix alloc_random_pkey() to make it really random
selftests/vm/pkeys: fix assertion in pkey_disable_set/clear()
selftests/vm/pkeys: fix pkey_disable_clear()
selftests: vm: pkeys: add helpers for pkey bits
...
|
|
copy_strings_kernel is always used with a single argument,
adjust the calling convention to that.
Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Cc: Alexander Viro <viro@zeniv.linux.org.uk>
Link: http://lkml.kernel.org/r/20200501104105.2621149-2-hch@lst.de
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
|
|
Move the computation of creds from prepare_binfmt into begin_new_exec
so that the creds need only be computed once. This is just code
reorganization no semantic changes of any kind are made.
Moving the computation is safe. I have looked through the kernel and
verified none of the binfmts look at bprm->cred directly, and that
there are no helpers that look at bprm->cred indirectly. Which means
that it is not a problem to compute the bprm->cred later in the
execution flow as it is not used until it becomes current->cred.
A new function bprm_creds_from_file is added to contain the work that
needs to be done. bprm_creds_from_file first computes which file
bprm->executable or most likely bprm->file that the bprm->creds
will be computed from.
The funciton bprm_fill_uid is updated to receive the file instead of
accessing bprm->file. The now unnecessary work needed to reset the
bprm->cred->euid, and bprm->cred->egid is removed from brpm_fill_uid.
A small comment to document that bprm_fill_uid now only deals with the
work to handle suid and sgid files. The default case is already
heandled by prepare_exec_creds.
The function security_bprm_repopulate_creds is renamed
security_bprm_creds_from_file and now is explicitly passed the file
from which to compute the creds. The documentation of the
bprm_creds_from_file security hook is updated to explain when the hook
is called and what it needs to do. The file is passed from
cap_bprm_creds_from_file into get_file_caps so that the caps are
computed for the appropriate file. The now unnecessary work in
cap_bprm_creds_from_file to reset the ambient capabilites has been
removed. A small comment to document that the work of
cap_bprm_creds_from_file is to read capabilities from the files
secureity attribute and derive capabilities from the fact the
user had uid 0 has been added.
Reviewed-by: Kees Cook <keescook@chromium.org>
Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>
|
|
There is a small bug in the code that recomputes parts of bprm->cred
for every bprm->file. The code never recomputes the part of
clear_dangerous_personality_flags it is responsible for.
Which means that in practice if someone creates a sgid script
the interpreter will not be able to use any of:
READ_IMPLIES_EXEC
ADDR_NO_RANDOMIZE
ADDR_COMPAT_LAYOUT
MMAP_PAGE_ZERO.
This accentially clearing of personality flags probably does
not matter in practice because no one has complained
but it does make the code more difficult to understand.
Further remaining bug compatible prevents the recomputation from being
removed and replaced by simply computing bprm->cred once from the
final bprm->file.
Making this change removes the last behavior difference between
computing bprm->creds from the final file and recomputing
bprm->cred several times. Which allows this behavior change
to be justified for it's own reasons, and for any but hunts
looking into why the behavior changed to wind up here instead
of in the code that will follow that computes bprm->cred
from the final bprm->file.
This small logic bug appears to have existed since the code
started clearing dangerous personality bits.
History Tree: git://git.kernel.org/pub/scm/linux/kernel/git/tglx/history.git
Fixes: 1bb0fa189c6a ("[PATCH] NX: clean up legacy binary support")
Reviewed-by: Kees Cook <keescook@chromium.org>
Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>
|
|
Recursion in kernel code is generally a bad idea as it can overflow
the kernel stack. Recursion in exec also hides that the code is
looping and that the loop changes bprm->file.
Instead of recursing in search_binary_handler have the methods that
would recurse set bprm->interpreter and return 0. Modify exec_binprm
to loop when bprm->interpreter is set. Consolidate all of the
reassignments of bprm->file in that loop to make it clear what is
going on.
The structure of the new loop in exec_binprm is that all errors return
immediately, while successful completion (ret == 0 &&
!bprm->interpreter) just breaks out of the loop and runs what
exec_bprm has always run upon successful completion.
Fail if the an interpreter is being call after execfd has been set.
The code has never properly handled an interpreter being called with
execfd being set and with reassignments of bprm->file and the
assignment of bprm->executable in generic code it has finally become
possible to test and fail when if this problematic condition happens.
With the reassignments of bprm->file and the assignment of
bprm->executable moved into the generic code add a test to see if
bprm->executable is being reassigned.
In search_binary_handler remove the test for !bprm->file. With all
reassignments of bprm->file moved to exec_binprm bprm->file can never
be NULL in search_binary_handler.
Link: https://lkml.kernel.org/r/87sgfwyd84.fsf_-_@x220.int.ebiederm.org
Acked-by: Linus Torvalds <torvalds@linux-foundation.org>
Reviewed-by: Kees Cook <keescook@chromium.org>
Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>
|
|
Most of the support for passing the file descriptor of an executable
to an interpreter already lives in the generic code and in binfmt_elf.
Rework the fields in binfmt_elf that deal with executable file
descriptor passing to make executable file descriptor passing a first
class concept.
Move the fd_install from binfmt_misc into begin_new_exec after the new
creds have been installed. This means that accessing the file through
/proc/<pid>/fd/N is able to see the creds for the new executable
before allowing access to the new executables files.
Performing the install of the executables file descriptor after
the point of no return also means that nothing special needs to
be done on error. The exiting of the process will close all
of it's open files.
Move the would_dump from binfmt_misc into begin_new_exec right
after would_dump is called on the bprm->file. This makes it
obvious this case exists and that no nesting of bprm->file is
currently supported.
In binfmt_misc the movement of fd_install into generic code means
that it's special error exit path is no longer needed.
Link: https://lkml.kernel.org/r/87y2poyd91.fsf_-_@x220.int.ebiederm.org
Acked-by: Linus Torvalds <torvalds@linux-foundation.org>
Reviewed-by: Kees Cook <keescook@chromium.org>
Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>
|
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The code in prepare_binary_handler needs to be run every time
search_binary_handler is called so move the call into search_binary_handler
itself to make the code simpler and easier to understand.
Link: https://lkml.kernel.org/r/87d070zrvx.fsf_-_@x220.int.ebiederm.org
Acked-by: Linus Torvalds <torvalds@linux-foundation.org>
Reviewed-by: Kees Cook <keescook@chromium.org>
Reviewed-by: James Morris <jamorris@linux.microsoft.com>
Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>
|
|
Add a flag preserve_creds that binfmt_misc can set to prevent
credentials from being updated. This allows binfmt_misc to always
call prepare_binprm. Allowing the credential computation logic to be
consolidated.
Not replacing the credentials with the interpreters credentials is
safe because because an open file descriptor to the executable is
passed to the interpreter. As the interpreter does not need to
reopen the executable it is guaranteed to see the same file that
exec sees.
Ref: c407c033de84 ("[PATCH] binfmt_misc: improve calculation of interpreter's credentials")
Link: https://lkml.kernel.org/r/87imgszrwo.fsf_-_@x220.int.ebiederm.org
Acked-by: Linus Torvalds <torvalds@linux-foundation.org>
Reviewed-by: Kees Cook <keescook@chromium.org>
Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>
|
|
Rename bprm->cap_elevated to bprm->active_secureexec and initialize it
in prepare_binprm instead of in cap_bprm_set_creds. Initializing
bprm->active_secureexec in prepare_binprm allows multiple
implementations of security_bprm_repopulate_creds to play nicely with
each other.
Rename security_bprm_set_creds to security_bprm_reopulate_creds to
emphasize that this path recomputes part of bprm->cred. This
recomputation avoids the time of check vs time of use problems that
are inherent in unix #! interpreters.
In short two renames and a move in the location of initializing
bprm->active_secureexec.
Link: https://lkml.kernel.org/r/87o8qkzrxp.fsf_-_@x220.int.ebiederm.org
Acked-by: Linus Torvalds <torvalds@linux-foundation.org>
Reviewed-by: Kees Cook <keescook@chromium.org>
Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>
|
|
Today security_bprm_set_creds has several implementations:
apparmor_bprm_set_creds, cap_bprm_set_creds, selinux_bprm_set_creds,
smack_bprm_set_creds, and tomoyo_bprm_set_creds.
Except for cap_bprm_set_creds they all test bprm->called_set_creds and
return immediately if it is true. The function cap_bprm_set_creds
ignores bprm->calld_sed_creds entirely.
Create a new LSM hook security_bprm_creds_for_exec that is called just
before prepare_binprm in __do_execve_file, resulting in a LSM hook
that is called exactly once for the entire of exec. Modify the bits
of security_bprm_set_creds that only want to be called once per exec
into security_bprm_creds_for_exec, leaving only cap_bprm_set_creds
behind.
Remove bprm->called_set_creds all of it's former users have been moved
to security_bprm_creds_for_exec.
Add or upate comments a appropriate to bring them up to date and
to reflect this change.
Link: https://lkml.kernel.org/r/87v9kszrzh.fsf_-_@x220.int.ebiederm.org
Acked-by: Linus Torvalds <torvalds@linux-foundation.org>
Acked-by: Casey Schaufler <casey@schaufler-ca.com> # For the LSM and Smack bits
Reviewed-by: Kees Cook <keescook@chromium.org>
Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>
|
|
There is and has been for a very long time been a lot more going on in
flush_old_exec than just flushing the old state. After the movement
of code from setup_new_exec there is a whole lot more going on than
just flushing the old executables state.
Rename flush_old_exec to begin_new_exec to more accurately reflect
what this function does.
Reviewed-by: Kees Cook <keescook@chromium.org>
Reviewed-by: Greg Ungerer <gerg@linux-m68k.org>
Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>
|
|
The two functions are now always called one right after the
other so merge them together to make future maintenance easier.
Reviewed-by: Kees Cook <keescook@chromium.org>
Reviewed-by: Greg Ungerer <gerg@linux-m68k.org>
Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>
|
|
Update the comments and make the code easier to understand by
renaming this flag.
Reviewed-by: Kees Cook <keescook@chromium.org>
Reviewed-by: Greg Ungerer <gerg@linux-m68k.org>
Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>
|
|
With install_exec_creds updated to follow immediately after
setup_new_exec, the failure of unshare_sighand is the only
code path where exec_update_mutex is held but not explicitly
unlocked.
Update that code path to explicitly unlock exec_update_mutex.
Remove the unlocking of exec_update_mutex from free_bprm.
Reviewed-by: Kees Cook <keescook@chromium.org>
Reviewed-by: Greg Ungerer <gerg@linux-m68k.org>
Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>
|
|
The cred_guard_mutex is problematic as it is held over possibly
indefinite waits for userspace. The possible indefinite waits for
userspace that I have identified are: The cred_guard_mutex is held in
PTRACE_EVENT_EXIT waiting for the tracer. The cred_guard_mutex is
held over "put_user(0, tsk->clear_child_tid)" in exit_mm(). The
cred_guard_mutex is held over "get_user(futex_offset, ...") in
exit_robust_list. The cred_guard_mutex held over copy_strings.
The functions get_user and put_user can trigger a page fault which can
potentially wait indefinitely in the case of userfaultfd or if
userspace implements part of the page fault path.
In any of those cases the userspace process that the kernel is waiting
for might make a different system call that winds up taking the
cred_guard_mutex and result in deadlock.
Holding a mutex over any of those possibly indefinite waits for
userspace does not appear necessary. Add exec_update_mutex that will
just cover updating the process during exec where the permissions and
the objects pointed to by the task struct may be out of sync.
The plan is to switch the users of cred_guard_mutex to
exec_update_mutex one by one. This lets us move forward while still
being careful and not introducing any regressions.
Link: https://lore.kernel.org/lkml/20160921152946.GA24210@dhcp22.suse.cz/
Link: https://lore.kernel.org/lkml/AM6PR03MB5170B06F3A2B75EFB98D071AE4E60@AM6PR03MB5170.eurprd03.prod.outlook.com/
Link: https://lore.kernel.org/linux-fsdevel/20161102181806.GB1112@redhat.com/
Link: https://lore.kernel.org/lkml/20160923095031.GA14923@redhat.com/
Link: https://lore.kernel.org/lkml/20170213141452.GA30203@redhat.com/
Ref: 45c1a159b85b ("Add PTRACE_O_TRACEVFORKDONE and PTRACE_O_TRACEEXIT facilities.")
Ref: 456f17cd1a28 ("[PATCH] user-vm-unlock-2.5.31-A2")
Reviewed-by: Kirill Tkhai <ktkhai@virtuozzo.com>
Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>
Signed-off-by: Bernd Edlinger <bernd.edlinger@hotmail.de>
Signed-off-by: Eric W. Biederman <ebiederm@xmission.com>
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struct linux_binprm::buf is the first field and it is exactly 128 bytes
in size. It means that on x86_64 all accesses to other fields will go
though [r64 + disp32] addressing mode which is 3 bytes bloatier than
[r64 + disp8] addressing mode. Given that accesses to other fields
outnumber accesses to ->buf, move it down.
Space savings (x86_64 defconfig):
more on distro configs because LSMs actively dereference "bprm"
but do not care about first 128 bytes of the executable itself.
add/remove: 0/0 grow/shrink: 0/24 up/down: 0/-492 (-492)
Function old new delta
selinux_bprm_committing_creds 552 549 -3
finalize_exec 94 91 -3
__audit_log_bprm_fcaps 283 280 -3
__audit_bprm 39 36 -3
perf_trace_sched_process_exec 347 341 -6
install_exec_creds 105 99 -6
cap_bprm_set_creds.cold 60 54 -6
would_dump 137 128 -9
load_script 637 628 -9
bprm_change_interp 61 52 -9
trace_event_raw_event_sched_process_exec 260 250 -10
search_binary_handler 255 240 -15
remove_arg_zero 295 277 -18
free_bprm 119 101 -18
prepare_binprm 379 360 -19
setup_new_exec 336 315 -21
flush_old_exec 1638 1617 -21
copy_strings.isra 746 724 -22
setup_arg_pages 559 530 -29
load_misc_binary 1151 1118 -33
selinux_bprm_set_creds 792 753 -39
load_elf_binary 11111 11072 -39
cap_bprm_set_creds 1496 1454 -42
__do_execve_file.isra 2395 2286 -109
Link: http://lkml.kernel.org/r/20190421165025.GA26843@avx2
Signed-off-by: Alexey Dobriyan <adobriyan@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
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git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs
Pull trivial vfs updates from Al Viro:
"A few cleanups + Neil's namespace_unlock() optimization"
* 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs:
exec: make prepare_bprm_creds static
genheaders: %-<width>s had been there since v6; %-*s - since v7
VFS: use synchronize_rcu_expedited() in namespace_unlock()
iov_iter: reduce code duplication
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get_arg_page() checks bprm->rlim_stack.rlim_cur and re-calculates the
"extra" size for argv/envp pointers every time, this is a bit ugly and
even not strictly correct: acct_arg_size() must not account this size.
Remove all the rlimit code in get_arg_page(). Instead, add bprm->argmin
calculated once at the start of __do_execve_file() and change
copy_strings to check bprm->p >= bprm->argmin.
The patch adds the new helper, prepare_arg_pages() which initializes
bprm->argc/envc and bprm->argmin.
[oleg@redhat.com: fix !CONFIG_MMU version of get_arg_page()]
Link: http://lkml.kernel.org/r/20181126122307.GA1660@redhat.com
[akpm@linux-foundation.org: use max_t]
Link: http://lkml.kernel.org/r/20181112160910.GA28440@redhat.com
Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Acked-by: Kees Cook <keescook@chromium.org>
Tested-by: Guenter Roeck <linux@roeck-us.net>
Cc: "Eric W. Biederman" <ebiederm@xmission.com>
Cc: Michal Hocko <mhocko@suse.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
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prepare_bprm_creds is not used outside exec.c, so there's no reason for it
to have external linkage.
Signed-off-by: Chanho Min <chanho.min@lge.com>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
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Linus recently observed that if we did not worry about the padding
member in struct siginfo it is only about 48 bytes, and 48 bytes is
much nicer than 128 bytes for allocating on the stack and copying
around in the kernel.
The obvious thing of only adding the padding when userspace is
including siginfo.h won't work as there are sigframe definitions in
the kernel that embed struct siginfo.
So split siginfo in two; kernel_siginfo and siginfo. Keeping the
traditional name for the userspace definition. While the version that
is used internally to the kernel and ultimately will not be padded to
128 bytes is called kernel_siginfo.
The definition of struct kernel_siginfo I have put in include/signal_types.h
A set of buildtime checks has been added to verify the two structures have
the same field offsets.
To make it easy to verify the change kernel_siginfo retains the same
size as siginfo. The reduction in size comes in a following change.
Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>
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Introduce helper:
int fork_usermode_blob(void *data, size_t len, struct umh_info *info);
struct umh_info {
struct file *pipe_to_umh;
struct file *pipe_from_umh;
pid_t pid;
};
that GPLed kernel modules (signed or unsigned) can use it to execute part
of its own data as swappable user mode process.
The kernel will do:
- allocate a unique file in tmpfs
- populate that file with [data, data + len] bytes
- user-mode-helper code will do_execve that file and, before the process
starts, the kernel will create two unix pipes for bidirectional
communication between kernel module and umh
- close tmpfs file, effectively deleting it
- the fork_usermode_blob will return zero on success and populate
'struct umh_info' with two unix pipes and the pid of the user process
As the first step in the development of the bpfilter project
the fork_usermode_blob() helper is introduced to allow user mode code
to be invoked from a kernel module. The idea is that user mode code plus
normal kernel module code are built as part of the kernel build
and installed as traditional kernel module into distro specified location,
such that from a distribution point of view, there is
no difference between regular kernel modules and kernel modules + umh code.
Such modules can be signed, modprobed, rmmod, etc. The use of this new helper
by a kernel module doesn't make it any special from kernel and user space
tooling point of view.
Such approach enables kernel to delegate functionality traditionally done
by the kernel modules into the user space processes (either root or !root) and
reduces security attack surface of the new code. The buggy umh code would crash
the user process, but not the kernel. Another advantage is that umh code
of the kernel module can be debugged and tested out of user space
(e.g. opening the possibility to run clang sanitizers, fuzzers or
user space test suites on the umh code).
In case of the bpfilter project such architecture allows complex control plane
to be done in the user space while bpf based data plane stays in the kernel.
Since umh can crash, can be oom-ed by the kernel, killed by the admin,
the kernel module that uses them (like bpfilter) needs to manage life
time of umh on its own via two unix pipes and the pid of umh.
The exit code of such kernel module should kill the umh it started,
so that rmmod of the kernel module will cleanup the corresponding umh.
Just like if the kernel module does kmalloc() it should kfree() it
in the exit code.
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: David S. Miller <davem@davemloft.net>
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Since the stack rlimit is used in multiple places during exec and it can
be changed via other threads (via setrlimit()) or processes (via
prlimit()), the assumption that the value doesn't change cannot be made.
This leads to races with mm layout selection and argument size
calculations. This changes the exec path to use the rlimit stored in
bprm instead of in current. Before starting the thread, the bprm stack
rlimit is stored back to current.
Link: http://lkml.kernel.org/r/1518638796-20819-4-git-send-email-keescook@chromium.org
Fixes: 64701dee4178e ("exec: Use sane stack rlimit under secureexec")
Signed-off-by: Kees Cook <keescook@chromium.org>
Reported-by: Ben Hutchings <ben.hutchings@codethink.co.uk>
Reported-by: Andy Lutomirski <luto@kernel.org>
Reported-by: Brad Spengler <spender@grsecurity.net>
Acked-by: Michal Hocko <mhocko@suse.com>
Cc: Ben Hutchings <ben@decadent.org.uk>
Cc: Greg KH <greg@kroah.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: "Jason A. Donenfeld" <Jason@zx2c4.com>
Cc: Laura Abbott <labbott@redhat.com>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Willy Tarreau <w@1wt.eu>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
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Provide a final callback into fs/exec.c before start_thread() takes
over, to handle any last-minute changes, like the coming restoration of
the stack limit.
Link: http://lkml.kernel.org/r/1518638796-20819-3-git-send-email-keescook@chromium.org
Signed-off-by: Kees Cook <keescook@chromium.org>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Ben Hutchings <ben@decadent.org.uk>
Cc: Ben Hutchings <ben.hutchings@codethink.co.uk>
Cc: Brad Spengler <spender@grsecurity.net>
Cc: Greg KH <greg@kroah.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: "Jason A. Donenfeld" <Jason@zx2c4.com>
Cc: Laura Abbott <labbott@redhat.com>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Willy Tarreau <w@1wt.eu>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
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Many source files in the tree are missing licensing information, which
makes it harder for compliance tools to determine the correct license.
By default all files without license information are under the default
license of the kernel, which is GPL version 2.
Update the files which contain no license information with the 'GPL-2.0'
SPDX license identifier. The SPDX identifier is a legally binding
shorthand, which can be used instead of the full boiler plate text.
This patch is based on work done by Thomas Gleixner and Kate Stewart and
Philippe Ombredanne.
How this work was done:
Patches were generated and checked against linux-4.14-rc6 for a subset of
the use cases:
- file had no licensing information it it.
- file was a */uapi/* one with no licensing information in it,
- file was a */uapi/* one with existing licensing information,
Further patches will be generated in subsequent months to fix up cases
where non-standard license headers were used, and references to license
had to be inferred by heuristics based on keywords.
The analysis to determine which SPDX License Identifier to be applied to
a file was done in a spreadsheet of side by side results from of the
output of two independent scanners (ScanCode & Windriver) producing SPDX
tag:value files created by Philippe Ombredanne. Philippe prepared the
base worksheet, and did an initial spot review of a few 1000 files.
The 4.13 kernel was the starting point of the analysis with 60,537 files
assessed. Kate Stewart did a file by file comparison of the scanner
results in the spreadsheet to determine which SPDX license identifier(s)
to be applied to the file. She confirmed any determination that was not
immediately clear with lawyers working with the Linux Foundation.
Criteria used to select files for SPDX license identifier tagging was:
- Files considered eligible had to be source code files.
- Make and config files were included as candidates if they contained >5
lines of source
- File already had some variant of a license header in it (even if <5
lines).
All documentation files were explicitly excluded.
The following heuristics were used to determine which SPDX license
identifiers to apply.
- when both scanners couldn't find any license traces, file was
considered to have no license information in it, and the top level
COPYING file license applied.
For non */uapi/* files that summary was:
SPDX license identifier # files
---------------------------------------------------|-------
GPL-2.0 11139
and resulted in the first patch in this series.
If that file was a */uapi/* path one, it was "GPL-2.0 WITH
Linux-syscall-note" otherwise it was "GPL-2.0". Results of that was:
SPDX license identifier # files
---------------------------------------------------|-------
GPL-2.0 WITH Linux-syscall-note 930
and resulted in the second patch in this series.
- if a file had some form of licensing information in it, and was one
of the */uapi/* ones, it was denoted with the Linux-syscall-note if
any GPL family license was found in the file or had no licensing in
it (per prior point). Results summary:
SPDX license identifier # files
---------------------------------------------------|------
GPL-2.0 WITH Linux-syscall-note 270
GPL-2.0+ WITH Linux-syscall-note 169
((GPL-2.0 WITH Linux-syscall-note) OR BSD-2-Clause) 21
((GPL-2.0 WITH Linux-syscall-note) OR BSD-3-Clause) 17
LGPL-2.1+ WITH Linux-syscall-note 15
GPL-1.0+ WITH Linux-syscall-note 14
((GPL-2.0+ WITH Linux-syscall-note) OR BSD-3-Clause) 5
LGPL-2.0+ WITH Linux-syscall-note 4
LGPL-2.1 WITH Linux-syscall-note 3
((GPL-2.0 WITH Linux-syscall-note) OR MIT) 3
((GPL-2.0 WITH Linux-syscall-note) AND MIT) 1
and that resulted in the third patch in this series.
- when the two scanners agreed on the detected license(s), that became
the concluded license(s).
- when there was disagreement between the two scanners (one detected a
license but the other didn't, or they both detected different
licenses) a manual inspection of the file occurred.
- In most cases a manual inspection of the information in the file
resulted in a clear resolution of the license that should apply (and
which scanner probably needed to revisit its heuristics).
- When it was not immediately clear, the license identifier was
confirmed with lawyers working with the Linux Foundation.
- If there was any question as to the appropriate license identifier,
the file was flagged for further research and to be revisited later
in time.
In total, over 70 hours of logged manual review was done on the
spreadsheet to determine the SPDX license identifiers to apply to the
source files by Kate, Philippe, Thomas and, in some cases, confirmation
by lawyers working with the Linux Foundation.
Kate also obtained a third independent scan of the 4.13 code base from
FOSSology, and compared selected files where the other two scanners
disagreed against that SPDX file, to see if there was new insights. The
Windriver scanner is based on an older version of FOSSology in part, so
they are related.
Thomas did random spot checks in about 500 files from the spreadsheets
for the uapi headers and agreed with SPDX license identifier in the
files he inspected. For the non-uapi files Thomas did random spot checks
in about 15000 files.
In initial set of patches against 4.14-rc6, 3 files were found to have
copy/paste license identifier errors, and have been fixed to reflect the
correct identifier.
Additionally Philippe spent 10 hours this week doing a detailed manual
inspection and review of the 12,461 patched files from the initial patch
version early this week with:
- a full scancode scan run, collecting the matched texts, detected
license ids and scores
- reviewing anything where there was a license detected (about 500+
files) to ensure that the applied SPDX license was correct
- reviewing anything where there was no detection but the patch license
was not GPL-2.0 WITH Linux-syscall-note to ensure that the applied
SPDX license was correct
This produced a worksheet with 20 files needing minor correction. This
worksheet was then exported into 3 different .csv files for the
different types of files to be modified.
These .csv files were then reviewed by Greg. Thomas wrote a script to
parse the csv files and add the proper SPDX tag to the file, in the
format that the file expected. This script was further refined by Greg
based on the output to detect more types of files automatically and to
distinguish between header and source .c files (which need different
comment types.) Finally Greg ran the script using the .csv files to
generate the patches.
Reviewed-by: Kate Stewart <kstewart@linuxfoundation.org>
Reviewed-by: Philippe Ombredanne <pombredanne@nexb.com>
Reviewed-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
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Patch series "exec: binfmt_misc: fix use-after-free, kill
iname[BINPRM_BUF_SIZE]".
It looks like this code was always wrong, then commit 948b701a607f
("binfmt_misc: add persistent opened binary handler for containers")
added more problems.
This patch (of 6):
load_script() can simply use i_name instead, it points into bprm->buf[]
and nobody can change this memory until we call prepare_binprm().
The only complication is that we need to also change the signature of
bprm_change_interp() but this change looks good too.
While at it, do whitespace/style cleanups.
NOTE: the real motivation for this change is that people want to
increase BINPRM_BUF_SIZE, we need to change load_misc_binary() too but
this looks more complicated because afaics it is very buggy.
Link: http://lkml.kernel.org/r/20170918163446.GA26793@redhat.com
Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Acked-by: Kees Cook <keescook@chromium.org>
Cc: Travis Gummels <tgummels@redhat.com>
Cc: Ben Woodard <woodard@redhat.com>
Cc: Jim Foraker <foraker1@llnl.gov>
Cc: <tdhooge@llnl.gov>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: James Bottomley <James.Bottomley@HansenPartnership.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
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Instead of a separate function, open-code the cap_elevated test, which
lets us entirely remove bprm->cap_effective (to use the local "effective"
variable instead), and more accurately examine euid/egid changes via the
existing local "is_setid".
The following LTP tests were run to validate the changes:
# ./runltp -f syscalls -s cap
# ./runltp -f securebits
# ./runltp -f cap_bounds
# ./runltp -f filecaps
All kernel selftests for capabilities and exec continue to pass as well.
Signed-off-by: Kees Cook <keescook@chromium.org>
Reviewed-by: James Morris <james.l.morris@oracle.com>
Acked-by: Serge Hallyn <serge@hallyn.com>
Reviewed-by: Andy Lutomirski <luto@kernel.org>
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