CVE-2026-52929: sctp: stream: fully roll back denied add-stream state

CVE-2026-52929: sctp: stream: fully roll back denied add-stream state

[Greg Kroah-Hartman]

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

Description
===========

In the Linux kernel, the following vulnerability has been resolved:

sctp: stream: fully roll back denied add-stream state

When ADD_OUT_STREAMS is denied, SCTP only shrinks the queued chunks and
then lowers outcnt. That leaves removed stream metadata behind, so a
later re-add can reuse a stale ext and hit a null-pointer dereference in
the scheduler get path.

Fix the rollback by tearing down the removed stream state the same way
other stream resizes do. Unschedule the current scheduler state, drop
the removed stream ext state with sctp_stream_outq_migrate(), and then
reschedule the remaining streams.

This keeps scheduler-private RR/FC/PRIO lists consistent while fully
rolling back denied outgoing stream additions.

The Linux kernel CVE team has assigned CVE-2026-52929 to this issue.


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

	Issue introduced in 4.15 with commit 637784ade221a3c8a7ecd0f583eddd95d6276b9a and fixed in 5.10.259 with commit 0cd2dc6dce8ca47212cd306ccd52eb315ef3cf85
	Issue introduced in 4.15 with commit 637784ade221a3c8a7ecd0f583eddd95d6276b9a and fixed in 5.15.210 with commit a6724b7b812ac8793514a1d5938db5d9d29ae725
	Issue introduced in 4.15 with commit 637784ade221a3c8a7ecd0f583eddd95d6276b9a and fixed in 6.1.176 with commit 9662eb0401518f0b4681f10e7fbf688f504f24cf
	Issue introduced in 4.15 with commit 637784ade221a3c8a7ecd0f583eddd95d6276b9a and fixed in 6.6.143 with commit 7dd9a42b044aad2dbe037db1c1e2943582485b44
	Issue introduced in 4.15 with commit 637784ade221a3c8a7ecd0f583eddd95d6276b9a and fixed in 6.12.94 with commit 39dc2b0eb5371a669ebc9ec6072b9184eac95418
	Issue introduced in 4.15 with commit 637784ade221a3c8a7ecd0f583eddd95d6276b9a and fixed in 6.18.36 with commit d5ea0b3e261fcb2cfff142675516165244cab1da
	Issue introduced in 4.15 with commit 637784ade221a3c8a7ecd0f583eddd95d6276b9a and fixed in 7.0.13 with commit 1c6773b8c081509dcd5cd2954f2b02c50c00f151
	Issue introduced in 4.15 with commit 637784ade221a3c8a7ecd0f583eddd95d6276b9a and fixed in 7.1 with commit a5f8a90ac9f77c678a9781c0a464b635e0d63e49

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-2026-52929
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/stream.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/0cd2dc6dce8ca47212cd306ccd52eb315ef3cf85
	https://git.kernel.org/stable/c/a6724b7b812ac8793514a1d5938db5d9d29ae725
	https://git.kernel.org/stable/c/9662eb0401518f0b4681f10e7fbf688f504f24cf
	https://git.kernel.org/stable/c/7dd9a42b044aad2dbe037db1c1e2943582485b44
	https://git.kernel.org/stable/c/39dc2b0eb5371a669ebc9ec6072b9184eac95418
	https://git.kernel.org/stable/c/d5ea0b3e261fcb2cfff142675516165244cab1da
	https://git.kernel.org/stable/c/1c6773b8c081509dcd5cd2954f2b02c50c00f151
	https://git.kernel.org/stable/c/a5f8a90ac9f77c678a9781c0a464b635e0d63e49