CVE-2026-74492: netfilter: ipset: do not update comments from kernel-side hash adds

From: Greg Kroah-Hartman <[email protected]>

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

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

netfilter: ipset: do not update comments from kernel-side hash adds

mtype_resize() copies comment pointers with memcpy(), not the comment
objects themselves. During the window after an entry has been copied but
before the table swap and backlog replay, the old table is still
published for packet-side updates while the replacement-table entry
already holds the same ip_set_comment_rcu pointer.

If xt_SET --add-set ... --exist hits that old entry in this window,
mtype_add() calls ip_set_init_comment() even though packet-side adds
carry no comment payload. That call frees the shared comment through the
old entry, so the replacement-table entry now holds a stale pointer.
When the queued add is replayed on the new table, mtype_add() calls
ip_set_init_comment() again and strlen() dereferences the stale pointer.

Fix this in mtype_add() by skipping ip_set_init_comment() when
ext->target marks a packet-side add. Userspace adds still update
comments, while packet-side adds can no longer free comment storage
shared with a resize copy.

The Linux kernel CVE team has assigned CVE-2026-74492 to this issue.


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

	Issue introduced in 5.6 with commit f66ee0410b1c3481ee75e5db9b34547b4d582465 and fixed in 6.6.151 with commit 661ff9c0cfbe07f8eed920dde9f7781491738207
	Issue introduced in 5.6 with commit f66ee0410b1c3481ee75e5db9b34547b4d582465 and fixed in 6.12.103 with commit c710e9bf38e4e71a8db85d26a0f70c0674664207
	Issue introduced in 5.6 with commit f66ee0410b1c3481ee75e5db9b34547b4d582465 and fixed in 6.18.44 with commit 4ae701848e4ba9e9713375fb7d82218cbd309da2
	Issue introduced in 5.6 with commit f66ee0410b1c3481ee75e5db9b34547b4d582465 and fixed in 7.1.8 with commit 77dbb248a5cc7a5270cd37bbb0b635bf059a872a
	Issue introduced in 5.6 with commit f66ee0410b1c3481ee75e5db9b34547b4d582465 and fixed in 7.2-rc6 with commit f30415929be8aeb002d557c8d3f7ab2d2188003a
	Issue introduced in 5.4.24 with commit 5dd9488ae41070b69d2f4acb580f77db5705f9ca
	Issue introduced in 5.5.8 with commit a469bab3386aebff33c59506f3a95e35b91118fd

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-2026-74492
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/netfilter/ipset/ip_set_hash_gen.h


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/661ff9c0cfbe07f8eed920dde9f7781491738207
	https://git.kernel.org/stable/c/c710e9bf38e4e71a8db85d26a0f70c0674664207
	https://git.kernel.org/stable/c/4ae701848e4ba9e9713375fb7d82218cbd309da2
	https://git.kernel.org/stable/c/77dbb248a5cc7a5270cd37bbb0b635bf059a872a
	https://git.kernel.org/stable/c/f30415929be8aeb002d557c8d3f7ab2d2188003a