[PATCH] sctp: hold shkey across socket migration

[PATCH] sctp: hold shkey across socket migration

[David Lee]

sctp_sock_migrate() transfers queued DATA skbs from the old socket to
the new one. skb_orphan() invokes sctp_wfree() during that transfer and
drops the skb-owned shared-key reference.

If userspace has removed that key from the association, this can be the
final reference. The following sctp_set_owner_w() then dereferences the
freed chunk->shkey while trying to take the new owner reference.

Take a temporary shared-key reference before orphaning the skb and
release it after the new owner has taken its reference. This preserves
the selected authentication key throughout the ownership transfer.

Fixes: 1b1e0bc99474 ("sctp: add refcnt support for sh_key")
Bug found and triaged by OpenAI Security Research and 
validated by Trail of Bits.

Assisted-by: Codex:gpt-5.6-sol gpt-5.5-cyber
Signed-off-by: Kyle Zeng <kylebot@openai.com>
---
Trail of Bits has a reproducer for this bug that triggers a 
KASAN use-after-free and can share if needed.

 net/sctp/socket.c | 12 +++++++++++-
 1 file changed, 11 insertions(+), 1 deletion(-)

diff --git a/net/sctp/socket.c b/net/sctp/socket.c
index c7b9e325e..4a08023d5 100644
--- a/net/sctp/socket.c
+++ b/net/sctp/socket.c
@@ -147,9 +147,19 @@ static inline void sctp_set_owner_w(struct sctp_chunk *chunk)
 
 static void sctp_clear_owner_w(struct sctp_chunk *chunk)
 {
+	/* Keep the shkey alive until the new owner takes its reference. */
+	if (chunk->shkey)
+		sctp_auth_shkey_hold(chunk->shkey);
 	skb_orphan(chunk->skb);
 }
 
+static void sctp_set_owner_w_migrate(struct sctp_chunk *chunk)
+{
+	sctp_set_owner_w(chunk);
+	if (chunk->shkey)
+		sctp_auth_shkey_release(chunk->shkey);
+}
+
 #define traverse_and_process()	\
 do {				\
 	msg = chunk->msg;	\
@@ -9632,7 +9642,7 @@ static int sctp_sock_migrate(struct sock *oldsk, struct sock *newsk,
 	lock_sock_nested(newsk, SINGLE_DEPTH_NESTING);
 	sctp_for_each_tx_datachunk(assoc, true, sctp_clear_owner_w);
 	sctp_assoc_migrate(assoc, newsk);
-	sctp_for_each_tx_datachunk(assoc, false, sctp_set_owner_w);
+	sctp_for_each_tx_datachunk(assoc, false, sctp_set_owner_w_migrate);
 
 	/* If the association on the newsk is already closed before accept()
 	 * is called, set RCV_SHUTDOWN flag.
-- 
2.53.0

Re: [PATCH] sctp: hold shkey across socket migration

[Xin Long]

On Fri, Jul 31, 2026 at 8:06 AM David Lee <david.lee@trailofbits.com> wrote:
>
> sctp_sock_migrate() transfers queued DATA skbs from the old socket to
> the new one. skb_orphan() invokes sctp_wfree() during that transfer and
> drops the skb-owned shared-key reference.
>
> If userspace has removed that key from the association, this can be the
> final reference. The following sctp_set_owner_w() then dereferences the
> freed chunk->shkey while trying to take the new owner reference.
>
> Take a temporary shared-key reference before orphaning the skb and
> release it after the new owner has taken its reference. This preserves
> the selected authentication key throughout the ownership transfer.
>
> Fixes: 1b1e0bc99474 ("sctp: add refcnt support for sh_key")
> Bug found and triaged by OpenAI Security Research and
> validated by Trail of Bits.
>
> Assisted-by: Codex:gpt-5.6-sol gpt-5.5-cyber
> Signed-off-by: Kyle Zeng <kylebot@openai.com>

The "Fixes: " is not together with others at the end, and the "Signed-off-by:"
for yourself is also missed:

Signed-off-by: David Lee <david.lee@trailofbits.com>

Patch looks good to me:

Acked-by: Xin Long <lucien.xin@gmail.com>

Not sure if you need to repost for fixing the tags, let's see.

Thanks.

Re: [PATCH] sctp: hold shkey across socket migration

[scott_gzh]

Hi Xin Long,

Is there any progress regarding this patch?

Best
Zihua GUO.

Re: [PATCH] sctp: hold shkey across socket migration

[Xin Long]

On Wed, Sep 9, 2026 at 10:08 PM <scott_gzh@163.com> wrote:
>
> Hi Xin Long,
>
> Is there any progress regarding this patch?
>

I think you need to post v2 with the tag issues addressed.

Thanks.

Re: [PATCH] sctp: hold shkey across socket migration

[Jun Yang]

Hi David and Xin,

My control-chunk migration fix [1] depends on this patch. Xin asked me
to wait for it to land so the dependent patch would apply.

Xin, would it be acceptable to send a v3 series carrying this patch as
1/2, without code changes, and my fix as 2/2? I would preserve David's
authorship, fix the tag placement noted in your review, and add my
sign-off.

David, could you provide the missing Signed-off-by requested in the
earlier review?

Thanks,
Jun

[1] https://lore.kernel.org/netdev/20260804113705.45754-1-juny24602@gmail.com/

Re: [PATCH] sctp: hold shkey across socket migration

[Xin Long]

On Wed, Sep 23, 2026 at 4:04 AM Jun Yang <juny24602@gmail.com> wrote:
>
> Hi David and Xin,
>
> My control-chunk migration fix [1] depends on this patch. Xin asked me
> to wait for it to land so the dependent patch would apply.
>
> Xin, would it be acceptable to send a v3 series carrying this patch as
> 1/2, without code changes, and my fix as 2/2? I would preserve David's
> authorship, fix the tag placement noted in your review, and add my
> sign-off.
Sure, sounds good to me.

Thanks.

>
> David, could you provide the missing Signed-off-by requested in the
> earlier review?
>
> Thanks,
> Jun
>
> [1] https://lore.kernel.org/netdev/20260804113705.45754-1-juny24602@gmail.com/