CVE-2026-80955: dm-pcache: fix use-after-free and invalid seg operations in kset_replay()

CVE-2026-80955: dm-pcache: fix use-after-free and invalid seg operations in kset_replay()

[Greg Kroah-Hartman]

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

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

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

dm-pcache: fix use-after-free and invalid seg operations in kset_replay()

In kset_replay, when key->seg_gen is stale (key->seg_gen <
key->cache_pos.cache_seg->gen), cache_key_put(key) is called but then
key->cache_pos.cache_seg is accessed as the argument to cache_seg_get().
This is a use-after-free on the freed key memory. Although mempool
recycled memory is not immediately reclaimed or overwritten in practice,
this is still a potential UAF bug.

Additionally, for expired invalid keys, setting the cache->seg_map bit
and calling cache_seg_get() is unreasonable since the corresponding
segment data is no longer valid.

Fix both issues by moving cache_seg_get() and __set_bit() after the
gen check, so they only execute for valid keys, and using continue to
skip invalid keys.

The Linux kernel CVE team has assigned CVE-2026-80955 to this issue.


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

	Issue introduced in 6.18 with commit 1d57628ff95b32d5cfa8d8f50e07690c161e9cf0 and fixed in 6.18.50 with commit 1894fc7a3bab90143dcd26ef8ee27040ef4a7501
	Issue introduced in 6.18 with commit 1d57628ff95b32d5cfa8d8f50e07690c161e9cf0 and fixed in 7.2.4 with commit f39a3e9cc5946473e16d6f5071b2ee0216c56d06
	Issue introduced in 6.18 with commit 1d57628ff95b32d5cfa8d8f50e07690c161e9cf0 and fixed in 7.3-rc1 with commit c2e894eac398b258f12fdec73ed6ba081047f7b3

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-2026-80955
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:
	drivers/md/dm-pcache/cache_key.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/1894fc7a3bab90143dcd26ef8ee27040ef4a7501
	https://git.kernel.org/stable/c/f39a3e9cc5946473e16d6f5071b2ee0216c56d06
	https://git.kernel.org/stable/c/c2e894eac398b258f12fdec73ed6ba081047f7b3