[PATCH net] sctp: clear control chunk transport if it is being removed

[PATCH net] sctp: clear control chunk transport if it is being removed

[Xin Long]

sctp_make_heartbeat_ack() caches the destination transport in
chunk->transport without taking a reference. When src_out_of_asoc_ok is
enabled, the HEARTBEAT ACK may remain queued on control_chunk_list instead
of being transmitted immediately.

If the peer transport is removed while the chunk is still queued,
sctp_assoc_rm_peer() drops the transport and schedules it for RCU freeing,
but only clears cached transport pointers in out_chunk_list.  The queued
control chunk therefore retains a dangling transport pointer.

Once an ASCONF_ACK clears the suppression and the queued control chunk is
transmitted, SCTP dereferences the stale transport pointer, leading to a
use-after-free.

Fix this by also clearing chunk->transport for queued control chunks in
control_chunk_list when removing the transport.

Fixes: 8a07eb0a50ae ("sctp: Add ASCONF operation on the single-homed host")
Reported-by: Daniele Linguaglossa <danielelinguaglossa@gmail.com>
Signed-off-by: Xin Long <lucien.xin@gmail.com>
---
 net/sctp/associola.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/net/sctp/associola.c b/net/sctp/associola.c
index b6ac0966420a..5b0ae616e1ff 100644
--- a/net/sctp/associola.c
+++ b/net/sctp/associola.c
@@ -573,6 +573,10 @@ void sctp_assoc_rm_peer(struct sctp_association *asoc,
 		if (ch->transport == peer)
 			ch->transport = NULL;
 
+	list_for_each_entry(ch, &asoc->outqueue.control_chunk_list, list)
+		if (ch->transport == peer)
+			ch->transport = NULL;
+
 	asoc->peer.transport_count--;
 
 	sctp_ulpevent_notify_peer_addr_change(peer, SCTP_ADDR_REMOVED, 0);
-- 
2.47.1

Re: [PATCH net] sctp: clear control chunk transport if it is being removed

[patchwork-bot+netdevbpf]

Hello:

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

On Wed,  5 Aug 2026 11:18:40 -0400 you wrote:
> sctp_make_heartbeat_ack() caches the destination transport in
> chunk->transport without taking a reference. When src_out_of_asoc_ok is
> enabled, the HEARTBEAT ACK may remain queued on control_chunk_list instead
> of being transmitted immediately.
> 
> If the peer transport is removed while the chunk is still queued,
> sctp_assoc_rm_peer() drops the transport and schedules it for RCU freeing,
> but only clears cached transport pointers in out_chunk_list.  The queued
> control chunk therefore retains a dangling transport pointer.
> 
> [...]

Here is the summary with links:
  - [net] sctp: clear control chunk transport if it is being removed
    https://git.kernel.org/netdev/net/c/c9158ceaf277

You are awesome, thank you!
-- 
Deet-doot-dot, I am a bot.
https://korg.docs.kernel.org/patchwork/pwbot.html