CVE-2026-89574: dm array: validate array block headers on read

CVE-2026-89574: dm array: validate array block headers on read

[Greg Kroah-Hartman]

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

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

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

dm array: validate array block headers on read

array_block_check() validates blocknr and csum and nothing else, while
node_check(), next to it, has bounded the structural fields since both
were written. dm_array_cursor_next() takes its loop bound from the
on-disk nr_entries and element_at() is unguarded pointer arithmetic, so
a count larger than the block holds keeps the cursor in one block while
the index grows past it and the read walks off the dm-bufio buffer --
dm_cache_load_mappings() drives it once per cache block at activation.

Check the header against itself: reject a zero value_size, require
max_entries to equal calc_max_entries() for that value_size and block
size, and require nr_entries to fit. Equality rather than an upper bound,
since a count below the real capacity trips BUG_ON() in fill_ablock() and
trim_ablock(). Metadata dm-array writes satisfies all three.

The Linux kernel CVE team has assigned CVE-2026-89574 to this issue.


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

	Issue introduced in 3.9 with commit 6513c29f44f2cc970c0e9fecfe5a6526c3e73025 and fixed in 6.12.109 with commit 67adda7ed5da3e3b64f5b9021a02c21fb374fd9c
	Issue introduced in 3.9 with commit 6513c29f44f2cc970c0e9fecfe5a6526c3e73025 and fixed in 6.18.50 with commit b33f76d33aaeacf3baf3370d8d64985169b36600
	Issue introduced in 3.9 with commit 6513c29f44f2cc970c0e9fecfe5a6526c3e73025 and fixed in 7.2.4 with commit 9808ddffb4bc659352df3020cd84d9d864820ee5
	Issue introduced in 3.9 with commit 6513c29f44f2cc970c0e9fecfe5a6526c3e73025 and fixed in 7.3-rc1 with commit 2965787723084835b18dfe993cd450ebf5bd4540

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-2026-89574
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/persistent-data/dm-array.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/67adda7ed5da3e3b64f5b9021a02c21fb374fd9c
	https://git.kernel.org/stable/c/b33f76d33aaeacf3baf3370d8d64985169b36600
	https://git.kernel.org/stable/c/9808ddffb4bc659352df3020cd84d9d864820ee5
	https://git.kernel.org/stable/c/2965787723084835b18dfe993cd450ebf5bd4540