CVE-2026-74588sctp: keep chunk->transport in step with the list it is queued on

Official description

In the Linux kernel, the following vulnerability has been resolved: sctp: keep chunk->transport in step with the list it is queued on __sctp_outq_flush_rtx() moves a gap-acked chunk onto another transport's transmitted list without updating chunk->transport: if (chunk->tsn_gap_acked) { list_move_tail(&chunk->transmitted_list, &transport->transmitted); continue; } The chunk then sits on a live transport's list while chunk->transport still names a different one. If that transport is removed - sctp_assoc_rm_peer() from an ASCONF Delete-IP - sctp_transport_free() RCU-frees it and the chunk is left with a dangling pointer. sctp_assoc_rm_peer() scrubs peer->transmitted and asoc->outqueue.out_chunk_list, but the chunk is on neither. The pointer is not followed while tsn_gap_acked is set. A SACK that reneges on the TSN clears the flag, and the next SACK reaches tchunk->transport->flight_size -= sctp_data_size(tchunk); inside the freed transport. KASAN reports a slab-use-after-free read in sctp_check_transmitted(), freed from sctp_assoc_rm_peer(). Both the removal and the SACKs come from the association peer. Set chunk->transport at the move. The ordinary resend path needs nothing: it reaches its list_move_tail() only after sctp_packet_append_chunk() returned SCTP_XMIT_OK, and __sctp_packet_append_chunk() has rebound the chunk by then. Discovered by XBOW, triaged by Baul Lee <baul.lee@xbow.com>

Affected packages & fixed versions

Affected products (as reported)

References

• https://git.kernel.org/stable/c/6575fb17230814b48b471727c8410c0aadff9274
• https://git.kernel.org/stable/c/6b9e2ea2057113f3393990ba646d2d97c719a80d
• https://git.kernel.org/stable/c/874a7c2b5e184f06134fdfde27e9ce9271bafe58
• https://git.kernel.org/stable/c/1adf929121e13e0b19200bb9fef715b918d483fe
• https://git.kernel.org/stable/c/e2e7c1de0e226ca1b7fea2de57a6c9bca408709b
• https://git.kernel.org/stable/c/2b3b5eec8b2c30ee237e3c31a6a38de9c39d804d
• https://git.kernel.org/stable/c/5ccf35ef0ed6059cdf8b1f4606a6584d5b67166b
• https://git.kernel.org/stable/c/9f2cf069a9a72a2d6b97ca8b4c70e714aac99749