CVE-2026-98586: sctp: hold asoc or transport before mod_timer() in timer handlers

CVE-2026-98586: sctp: hold asoc or transport before mod_timer() in timer handlers

[Greg Kroah-Hartman]

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

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

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

sctp: hold asoc or transport before mod_timer() in timer handlers

Take the association or transport reference before rearming a timer in the
timer handlers.

The existing code calls mod_timer() before taking the reference needed by
the rearmed timer without holding the sock lock. This creates a race with
timer cleanup: if the timer is deleted after mod_timer() returns but before
the reference is taken, the cleanup path can drop the timer's reference and
destroy the transport or association. The timer handler then takes a
reference on the already freed object and eventually drops it, causing a
refcount underflow.

Hold the object before mod_timer() and drop the reference if mod_timer()
reports that the timer was already pending in timer handlers. Apply the
same ordering to the proto-unreachable path, which can rearm a transport
timer outside the timer handlers without holding the sock lock.

The Linux kernel CVE team has assigned CVE-2026-98586 to this issue.


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

	Issue introduced in 2.6.12 with commit 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 and fixed in 5.15.222 with commit f7dea7eaea20fe9b80f8f77ba44d02b4a17f8050
	Issue introduced in 2.6.12 with commit 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 and fixed in 6.1.189 with commit f9d929026d487a988bfa12c065f892e823e5b6ab
	Issue introduced in 2.6.12 with commit 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 and fixed in 6.6.158 with commit 9d3d39da054476e7aa05cd877b93ca73a9a77434
	Issue introduced in 2.6.12 with commit 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 and fixed in 6.12.112 with commit 27c51a9b55b227309161c903f9ecfbf022516bc2
	Issue introduced in 2.6.12 with commit 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 and fixed in 6.18.55 with commit d18cb8fd1b6ba95c85de644203cfe1b071ff0c0f
	Issue introduced in 2.6.12 with commit 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 and fixed in 7.2.9 with commit 35bf3b23c9a871f44c1453d85f8332be4e088dda
	Issue introduced in 2.6.12 with commit 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 and fixed in 7.3-rc5 with commit cae23ae3f7887a1cf8a75da38edcebeef695040f

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-2026-98586
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/input.c
	net/sctp/sm_sideeffect.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/f7dea7eaea20fe9b80f8f77ba44d02b4a17f8050
	https://git.kernel.org/stable/c/f9d929026d487a988bfa12c065f892e823e5b6ab
	https://git.kernel.org/stable/c/9d3d39da054476e7aa05cd877b93ca73a9a77434
	https://git.kernel.org/stable/c/27c51a9b55b227309161c903f9ecfbf022516bc2
	https://git.kernel.org/stable/c/d18cb8fd1b6ba95c85de644203cfe1b071ff0c0f
	https://git.kernel.org/stable/c/35bf3b23c9a871f44c1453d85f8332be4e088dda
	https://git.kernel.org/stable/c/cae23ae3f7887a1cf8a75da38edcebeef695040f