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

[Greg Kroah-Hartman <gregkh@linuxfoundation.org>]

From: Greg Kroah-Hartman <gregkh@kernel.org>

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>

The Linux kernel CVE team has assigned CVE-2026-74588 to this issue.


Affected and fixed versions
===========================

	Issue introduced in 2.6.12 with commit 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 and fixed in 5.10.265 with commit 6575fb17230814b48b471727c8410c0aadff9274
	Issue introduced in 2.6.12 with commit 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 and fixed in 5.15.216 with commit 6b9e2ea2057113f3393990ba646d2d97c719a80d
	Issue introduced in 2.6.12 with commit 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 and fixed in 6.1.183 with commit 874a7c2b5e184f06134fdfde27e9ce9271bafe58
	Issue introduced in 2.6.12 with commit 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 and fixed in 6.6.152 with commit 1adf929121e13e0b19200bb9fef715b918d483fe
	Issue introduced in 2.6.12 with commit 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 and fixed in 6.12.104 with commit e2e7c1de0e226ca1b7fea2de57a6c9bca408709b
	Issue introduced in 2.6.12 with commit 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 and fixed in 6.18.45 with commit 2b3b5eec8b2c30ee237e3c31a6a38de9c39d804d
	Issue introduced in 2.6.12 with commit 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 and fixed in 7.1.9 with commit 5ccf35ef0ed6059cdf8b1f4606a6584d5b67166b
	Issue introduced in 2.6.12 with commit 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 and fixed in 7.2 with commit 9f2cf069a9a72a2d6b97ca8b4c70e714aac99749

Please see https://www.kernel.org for a full list of currently supported
kernel versions by the kernel community.

Unaffected versions might change over time as fixes are backported to
older supported kernel versions.  The official CVE entry at
	https://cve.org/CVERecord/?id=CVE-2026-74588
will be updated if fixes are backported, please check that for the most
up to date information about this issue.


Affected files
==============

The file(s) affected by this issue are:
	net/sctp/outqueue.c


Mitigation
==========

The Linux kernel CVE team recommends that you update to the latest
stable kernel version for this, and many other bugfixes.  Individual
changes are never tested alone, but rather are part of a larger kernel
release.  Cherry-picking individual commits is not recommended or
supported by the Linux kernel community at all.  If however, updating to
the latest release is impossible, the individual changes to resolve this
issue can be found at these commits:
	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