CVE-2026-80956: dm-pcache: only hand out initialized cache segments

CVE-2026-80956: dm-pcache: only hand out initialized cache segments

[Greg Kroah-Hartman]

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

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

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

dm-pcache: only hand out initialized cache segments

get_cache_segment() scans the segment map up to cache->n_segs, the
physical device segment count, but cache_segs_init() only initializes
the first cache_info->n_segs segments. A crafted image with
cache_info->n_segs smaller than the device count leaves the remaining
pcache_cache_segment structs zeroed (segment.data == NULL), and the
allocator can hand one to cache_kset_close(), which writes through the
returned segment's data pointer with no NULL check.

Bound the allocator's search to cache_info->n_segs so only initialized
segments are ever returned. A conforming cache sets n_segs equal to the
device segment count, so this rejects nothing legitimate.

The Linux kernel CVE team has assigned CVE-2026-80956 to this issue.


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

	Issue introduced in 6.18 with commit 1d57628ff95b32d5cfa8d8f50e07690c161e9cf0 and fixed in 6.18.50 with commit 83e3116283ed2c6a6a1fa662862a4b4d7d2701a2
	Issue introduced in 6.18 with commit 1d57628ff95b32d5cfa8d8f50e07690c161e9cf0 and fixed in 7.2.4 with commit 692037ae1a7cfacc2f0c22c6e034c1dfee0e553f
	Issue introduced in 6.18 with commit 1d57628ff95b32d5cfa8d8f50e07690c161e9cf0 and fixed in 7.3-rc1 with commit 2df0fc042e299bae3c0f60ea5cd2af9285658e9f

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-2026-80956
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_segment.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/83e3116283ed2c6a6a1fa662862a4b4d7d2701a2
	https://git.kernel.org/stable/c/692037ae1a7cfacc2f0c22c6e034c1dfee0e553f
	https://git.kernel.org/stable/c/2df0fc042e299bae3c0f60ea5cd2af9285658e9f