[PATCH] net/sched: act_api: avoid dereferencing ERR_PTR in tcf_idrinfo_destroy

[PATCH] net/sched: act_api: avoid dereferencing ERR_PTR in tcf_idrinfo_destroy

[Shivani Gupta]

syzbot reported a crash in tc_act_in_hw() during netns teardown where
tcf_idrinfo_destroy() passed an ERR_PTR(-EBUSY) value as a tc_action
pointer, leading to an invalid dereference.

Guard against ERR_PTR entries when iterating the action IDR so teardown
does not call tc_act_in_hw() on an error pointer.

Link: https://syzkaller.appspot.com/bug?extid=8f1c492ffa4644ff3826
Reported-by: syzbot+8f1c492ffa4644ff3826@syzkaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=8f1c492ffa4644ff3826
Signed-off-by: Shivani Gupta <shivani07g@gmail.com>
---
 net/sched/act_api.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/net/sched/act_api.c b/net/sched/act_api.c
index ff6be5cfe2b0..994f7ffe26a5 100644
--- a/net/sched/act_api.c
+++ b/net/sched/act_api.c
@@ -940,6 +940,10 @@ void tcf_idrinfo_destroy(const struct tc_action_ops *ops,
 	int ret;
 
 	idr_for_each_entry_ul(idr, p, tmp, id) {
+		if (IS_ERR(p)) {
+			WARN_ON_ONCE(1);
+			continue;
+		}
 		if (tc_act_in_hw(p) && !mutex_taken) {
 			rtnl_lock();
 			mutex_taken = true;
-- 
2.34.1

Re: [PATCH] net/sched: act_api: avoid dereferencing ERR_PTR in tcf_idrinfo_destroy

[Cong Wang]

On Fri, Jan 02, 2026 at 11:21:16PM +0000, Shivani Gupta wrote:
> syzbot reported a crash in tc_act_in_hw() during netns teardown where
> tcf_idrinfo_destroy() passed an ERR_PTR(-EBUSY) value as a tc_action
> pointer, leading to an invalid dereference.
> 
> Guard against ERR_PTR entries when iterating the action IDR so teardown
> does not call tc_act_in_hw() on an error pointer.
> 
> Link: https://syzkaller.appspot.com/bug?extid=8f1c492ffa4644ff3826
> Reported-by: syzbot+8f1c492ffa4644ff3826@syzkaller.appspotmail.com
> Closes: https://syzkaller.appspot.com/bug?extid=8f1c492ffa4644ff3826
> Signed-off-by: Shivani Gupta <shivani07g@gmail.com>

Thanks for the patch, Shivani.

Could you provide a Fixes tag for this while you are on it?

> ---
>  net/sched/act_api.c | 4 ++++
>  1 file changed, 4 insertions(+)
> 
> diff --git a/net/sched/act_api.c b/net/sched/act_api.c
> index ff6be5cfe2b0..994f7ffe26a5 100644
> --- a/net/sched/act_api.c
> +++ b/net/sched/act_api.c
> @@ -940,6 +940,10 @@ void tcf_idrinfo_destroy(const struct tc_action_ops *ops,
>  	int ret;
>  
>  	idr_for_each_entry_ul(idr, p, tmp, id) {
> +		if (IS_ERR(p)) {
> +			WARN_ON_ONCE(1);

Hm, I guess we should remove this warning here since ERR_PTR is expected
in some corner case?

Regards,
Cong Wang

[PATCH v2] net/sched: act_api: avoid dereferencing ERR_PTR in tcf_idrinfo_destroy

[Shivani Gupta]

syzbot reported a crash in tc_act_in_hw() during netns teardown where
tcf_idrinfo_destroy() passed an ERR_PTR(-EBUSY) value as a tc_action
pointer, leading to an invalid dereference.

Guard against ERR_PTR entries when iterating the action IDR so teardown
does not call tc_act_in_hw() on an error pointer.

Fixes: 84a7d6797e6a ("net/sched: acp_api: no longer acquire RTNL in tc_action_net_exit()")
Link: https://syzkaller.appspot.com/bug?extid=8f1c492ffa4644ff3826
Reported-by: syzbot+8f1c492ffa4644ff3826@syzkaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=8f1c492ffa4644ff3826
Signed-off-by: Shivani Gupta <shivani07g@gmail.com>
---
v2:
- Drop WARN_ON_ONCE() as ERR_PTR can be expected in a corner case.
- Add Fixes: tag.

 net/sched/act_api.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/net/sched/act_api.c b/net/sched/act_api.c
index ff6be5cfe2b0..5e0a196ce66a 100644
--- a/net/sched/act_api.c
+++ b/net/sched/act_api.c
@@ -940,6 +940,9 @@ void tcf_idrinfo_destroy(const struct tc_action_ops *ops,
 	int ret;
 
 	idr_for_each_entry_ul(idr, p, tmp, id) {
+		if (IS_ERR(p)) {
+			continue;
+		}
 		if (tc_act_in_hw(p) && !mutex_taken) {
 			rtnl_lock();
 			mutex_taken = true;
-- 
2.34.1

Re: [PATCH v2] net/sched: act_api: avoid dereferencing ERR_PTR in tcf_idrinfo_destroy

[patchwork-bot+netdevbpf]

Hello:

This patch was applied to netdev/net.git (main)
by Jakub Kicinski <kuba@kernel.org>:

On Mon,  5 Jan 2026 00:59:05 +0000 you wrote:
> syzbot reported a crash in tc_act_in_hw() during netns teardown where
> tcf_idrinfo_destroy() passed an ERR_PTR(-EBUSY) value as a tc_action
> pointer, leading to an invalid dereference.
> 
> Guard against ERR_PTR entries when iterating the action IDR so teardown
> does not call tc_act_in_hw() on an error pointer.
> 
> [...]

Here is the summary with links:
  - [v2] net/sched: act_api: avoid dereferencing ERR_PTR in tcf_idrinfo_destroy
    https://git.kernel.org/netdev/net/c/adb25a46dc0a

You are awesome, thank you!
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