net/sched: act_gact, act_police: range check the fallback control action

tcf_action_check_ctrlact() range checks the primary control action:

	if (!opcode)
		ret = action > TC_ACT_VALUE_MAX ? -EINVAL : 0;

TC_ACT_VALUE_MAX is TC_ACT_TRAP, so kernel-internal verdicts above it
cannot be set that way. But act_gact and act_police each carry a second,
independent control action supplied by user space that never reaches that
helper - TCA_GACT_PROB.paction and TCA_POLICE_RESULT. Both only reject
TC_ACT_GOTO_CHAIN, so any other value is stored verbatim and returned
verbatim from the action.

In particular user space can store TC_ACT_CONSUMED, which is
TC_ACT_VALUE_MAX + 1 and is deliberately not part of the UAPI value
range. That verdict tells every caller the action took ownership of the
skb, so nobody frees it: sch_handle_ingress(), sch_handle_egress() and
tcf_qevent_handle() all deliberately skip the free for it. The result is
one leaked sk_buff plus its data buffer per packet traversing the filter,
unbounded, for all traffic on the chain including kernel-generated
packets.

Both are trivially deterministic. act_gact clamps tcfg_pval to >= 1, so
with pval = 1 gact_determ() returns the fallback for every packet.
act_police has no mandatory rate, so rate = 0 leaves tcfp_mtu = ~0 and
tcf_police_mtu_check() always passes.

TC_ACT_CONSUMED was added by commit 720f22fed81b ("net: sched: refactor
reinsert action"), after both goto-chain guards were written:
commit 9469f375ab09 ("net/sched: act_gact: disallow 'goto chain' on
fallback control action") and
commit c08f5ed5d625 ("net/sched: act_police: disallow 'goto chain' on
fallback control action"). Neither guard was widened when the new
verdict appeared.

Factor the existing range test out of tcf_action_check_ctrlact() as
tcf_action_valid() and apply it to both fallbacks. The helper cannot call
tcf_action_check_ctrlact() directly because that also allocates a
goto_chain, which is exactly what these two sites must not do.

Reproduced on v7.2-rc6: kmemleak reports one leaked 232-byte
skbuff_head_cache object plus its 704-byte data buffer per packet. With
this patch both configurations are rejected with -EINVAL and kmemleak
reports none.

Fixes: 720f22fed81b ("net: sched: refactor reinsert action")
Cc: stable@vger.kernel.org # v5.3+
Signed-off-by: Hyunjung Ko <hj351016@gmail.com>
Acked-by: Jamal Hadi Salim <jhs@mojatatu.com>
Tested-by: Victor Nogueira <victor@mojatatu.com>
Link: https://patch.msgid.link/20260806101252.809593-1-hj351016@gmail.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

1 files changed, 19 insertions, 0 deletions

diff --git a/include/net/act_api.h b/include/net/act_api.h
index 20d9e55f8564..fd03f6319e88 100644
--- a/include/net/act_api.h
+++ b/include/net/act_api.h
@@ -270,6 +270,25 @@ int tcf_action_check_ctrlact(int action, struct tcf_proto *tp,
 struct tcf_chain *tcf_action_set_ctrlact(struct tc_action *a, int action,
 					 struct tcf_chain *newchain);
 
+/* Range check for a control action supplied by user space.
+ *
+ * This is the same test tcf_action_check_ctrlact() applies to the primary
+ * control action, factored out for the *fallback* control actions
+ * (act_gact's TCA_GACT_PROB.paction and act_police's TCA_POLICE_RESULT),
+ * which must not reach tcf_action_check_ctrlact() because they have no
+ * goto_chain to allocate.  Without it, user space can store kernel-internal
+ * verdicts such as TC_ACT_CONSUMED, which is TC_ACT_VALUE_MAX + 1 and is
+ * deliberately not part of the UAPI value range.
+ */
+static inline bool tcf_action_valid(int action)
+{
+	int opcode = TC_ACT_EXT_OPCODE(action);
+
+	if (!opcode)
+		return action <= TC_ACT_VALUE_MAX;
+	return opcode <= TC_ACT_EXT_OPCODE_MAX || action == TC_ACT_UNSPEC;
+}
+
 #ifdef CONFIG_INET
 DECLARE_STATIC_KEY_FALSE(tcf_frag_xmit_count);
 #endif