[PATCH net v2] net/sched: fix use-after-free in __tcf_action_put()

[Jérémy Jean]

__tcf_action_put() decrements the reference count before decrementing the
binding count. Another thread can free the action between these operations,
causing the binding-count update to access freed memory. KASAN reports it
as:

  BUG: KASAN: slab-use-after-free in __tcf_action_put+0x327/0x340
  Write of size 4 at addr ff11000000d46420 by task tc-put-pause/64

Hold the action IDR mutex across both counter updates and IDR removal,
keeping cleanup outside the lock.

Fixes: 16af6067392c ("net: sched: implement reference counted action release")
Cc: stable@xxxxxxxxxxxxxxx
Assisted-by: LLM
Signed-off-by: Jérémy Jean <Jeremy.Jean@xxxxxxxxxxxxxxxxx>
---

Change in v2:
- Invert the condition of the test.

v1: https://lore.kernel.org/all/20260930211839.620410-2-Jeremy.Jean@xxxxxxxxxxxxxxxxx/

 net/sched/act_api.c | 11 +++++------
 1 file changed, 5 insertions(+), 6 deletions(-)

diff --git a/net/sched/act_api.c b/net/sched/act_api.c
index e45a63be397c..9eb1dec14cb1 100644
--- a/net/sched/act_api.c
+++ b/net/sched/act_api.c
@@ -372,9 +372,10 @@ static int __tcf_action_put(struct tc_action *p, bool bind)
 {
 	struct tcf_idrinfo *idrinfo = p->idrinfo;
 
-	if (refcount_dec_and_mutex_lock(&p->tcfa_refcnt, &idrinfo->lock)) {
-		if (bind)
-			atomic_dec(&p->tcfa_bindcnt);
+	mutex_lock(&idrinfo->lock);
+	if (bind)
+		atomic_dec(&p->tcfa_bindcnt);
+	if (refcount_dec_and_test(&p->tcfa_refcnt)) {
 		idr_remove(&idrinfo->action_idr, p->tcfa_index);
 		mutex_unlock(&idrinfo->lock);
 
@@ -382,9 +383,7 @@ static int __tcf_action_put(struct tc_action *p, bool bind)
 		return 1;
 	}
 
-	if (bind)
-		atomic_dec(&p->tcfa_bindcnt);
-
+	mutex_unlock(&idrinfo->lock);
 	return 0;
 }
 
-- 
2.47.3