Merge branch 'bpf-compare-iterator-types-during-state-pruning'

Ning Ding says:

====================
bpf: Compare iterator types during state pruning

Iterator stack slots can be marked MEM_RCU or PTR_UNTRUSTED. The
STACK_ITER check in stacksafe() does not compare this type, so state
pruning can treat these states as equal and prune an unsafe path.

Compare the type and add a test where RCU protection has a gap.
---
Changes in v2:
- Convert the regression test to inline assembly so its verifier-sensitive
  control-flow layout is stable.
- Add Eduard Zingerman's Acked-by tag to patch 1.

v1: https://lore.kernel.org/bpf/20260807004320.134069-1-dingning04@gmail.com/
====================

Link: https://patch.msgid.link/20260811035955.132989-1-dingning04@gmail.com
Signed-off-by: Eduard Zingerman <eddyz87@gmail.com>

2 files changed, 48 insertions, 1 deletions

diff --git a/kernel/bpf/states.c b/kernel/bpf/states.c
index ea2153cf28d0..4e6aafad33bd 100644
--- a/kernel/bpf/states.c
+++ b/kernel/bpf/states.c
@@ -812,7 +812,8 @@ static bool stacksafe(struct bpf_verifier_env *env, struct bpf_func_state *old,
 			 * infinite loop check triggering, see
 			 * iter_active_depths_differ()
 			 */
-			if (old_reg->iter.btf != cur_reg->iter.btf ||
+			if (old_reg->type != cur_reg->type ||
+			    old_reg->iter.btf != cur_reg->iter.btf ||
 			    old_reg->iter.btf_id != cur_reg->iter.btf_id ||
 			    old_reg->iter.state != cur_reg->iter.state ||
 			    /* ignore {old_reg,cur_reg}->iter.depth, see above */
diff --git a/tools/testing/selftests/bpf/progs/iters_task_failure.c b/tools/testing/selftests/bpf/progs/iters_task_failure.c
index fe3663dedbe1..566a1d3dffea 100644
--- a/tools/testing/selftests/bpf/progs/iters_task_failure.c
+++ b/tools/testing/selftests/bpf/progs/iters_task_failure.c
@@ -62,6 +62,52 @@ int BPF_PROG(iter_tasks_lock_and_unlock)
 }
 
 SEC("?fentry.s/" SYS_PREFIX "sys_getpgid")
+__failure __msg("expected an RCU CS when using bpf_iter_task_next")
+__flag(BPF_F_TEST_STATE_FREQ)
+int BPF_PROG(iter_tasks_rcu_state_pruning)
+{
+	struct bpf_iter_task it;
+
+	asm volatile (
+		"call %[bpf_rcu_read_lock];"
+		"r1 = %[it];"
+		"r2 = 0;"
+		"r3 = 0;" /* BPF_TASK_ITER_ALL_PROCS */
+		"call %[bpf_iter_task_new];"
+
+		"call %[bpf_get_prandom_u32];"
+		"if w0 == 0 goto unprotected_%=;"
+
+		/* Keep the outer RCU lock active on the straight-line path. */
+		"call %[bpf_rcu_read_lock];"
+		"call %[bpf_rcu_read_unlock];"
+		"goto merge_%=;"
+
+	"unprotected_%=:"
+		/* Create an unprotected gap on the taken path. */
+		"call %[bpf_rcu_read_unlock];"
+		"call %[bpf_rcu_read_lock];"
+
+	"merge_%=: r1 = %[it];"
+		"call %[bpf_iter_task_next];"
+		"r1 = %[it];"
+		"call %[bpf_iter_task_destroy];"
+		"call %[bpf_rcu_read_unlock];"
+		:
+		: __imm_ptr(it),
+		  __imm(bpf_get_prandom_u32),
+		  __imm(bpf_iter_task_new),
+		  __imm(bpf_iter_task_next),
+		  __imm(bpf_iter_task_destroy),
+		  __imm(bpf_rcu_read_lock),
+		  __imm(bpf_rcu_read_unlock)
+		: __clobber_common
+	);
+
+	return 0;
+}
+
+SEC("?fentry.s/" SYS_PREFIX "sys_getpgid")
 __failure __msg("expected an RCU CS when using bpf_iter_css_next")
 int BPF_PROG(iter_css_lock_and_unlock)
 {