Re: [PATCH net] net/sched: reject IDR error pointers when deleting actions
From: Jamal Hadi Salim <jhs@mojatatu.com>
Date: 2026-09-14 09:58:44
Also in:
lkml
On Mon, Sep 14, 2026 at 2:51 AM Weiming Shi [off-list ref] wrote:
tcf_action_delete() drops the reference held by its lookup before calling
tcf_idr_delete_index() with the saved action index. An unlocked
classifier can remove that action and reserve the same IDR slot with
ERR_PTR(-EBUSY) in between.
tcf_idr_delete_index() only checks the lookup result for NULL. It
therefore treats the reservation as a tc_action and dereferences
tcfa_bindcnt. A hardware execution breakpoint was used to schedule the
interleaving without changing the kernel source. KASAN reported this
decoded trace:
BUG: KASAN: null-ptr-deref in tca_action_gd+0x5b9/0x1010
Read of size 4 at addr 0000000000000010 by task poc/150
Oops: general protection fault, probably for non-canonical address 0xdffffc0000000002
RIP: tca_action_gd+0x5c0/0x1010:
arch_atomic_read at arch/x86/include/asm/atomic.h:23
raw_atomic_read at include/linux/atomic/atomic-arch-fallback.h:457
atomic_read at include/linux/atomic/atomic-instrumented.h:33
tcf_idr_delete_index at net/sched/act_api.c:766
tcf_action_delete at net/sched/act_api.c:1859
tcf_del_notify at net/sched/act_api.c:2014
tca_action_gd at net/sched/act_api.c:2064
R13: 0000000000000010 R15: fffffffffffffff0
Kernel panic - not syncing: Fatal exception
R15 contains ERR_PTR(-EBUSY), and adding the tcfa_bindcnt offset produces
the address in R13. With the guard applied, the same reproducer returned
-ENOENT without a KASAN report or panic. Treat error pointers as absent
and return -ENOENT.We test all submissions to tc. Can you provide a tdc test or reproducer (PoC)? Please remember tto do his for any future submissions. If the information is sensitive, please send it to me privately. cheer, jamal
quoted hunk ↗ jump to hunk
Fixes: 0190c1d452a9 ("net: sched: atomically check-allocate action") Cc: stable@vger.kernel.org Reported-by: Xiang Mei <redacted> Assisted-by: LLM Signed-off-by: Weiming Shi <redacted> --- net/sched/act_api.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)diff --git a/net/sched/act_api.c b/net/sched/act_api.c index 19501dc99..eabe612b7 100644 --- a/net/sched/act_api.c +++ b/net/sched/act_api.c@@ -758,7 +758,7 @@ static int tcf_idr_delete_index(struct tcf_idrinfo *idrinfo, u32 index) mutex_lock(&idrinfo->lock); p = idr_find(&idrinfo->action_idr, index); - if (!p) { + if (IS_ERR_OR_NULL(p)) { mutex_unlock(&idrinfo->lock); return -ENOENT; }base-commit: e6b6078ea1731b05b3b552497b3bce4bf8b014ae -- 2.55.0