CVE-2026-74643: samples/damon/mtier: error out for zero quota goal target values

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

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

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

samples/damon/mtier: error out for zero quota goal target values

Patch series "mm/damon: avoid division by zero from damos_quota_score()".

DAMON_SAMPLE_MTIER and DAMON_LRU_SORT allow the user to trigger division
by zero in damos_quota_score().  Avoid it by adding parameters validation
checks.


This patch (of 2):

damos_quota_score() can trigger division by zero if the target_value is
zero.  DAMON_SAMPLE_MTIER lets users set the target_value via
node0_mem_{used,free}_bp parameters.  It doesn't guard zero value case,
though.  As a result, users can trigger division by zero.  Fix the issue
by returning an error when the user tries to start DAMON with zero
node0_mem_{used,free}_bp parameter values.

DAMON_SAMPLE_MTIER is just a sample module, but the consequence is quite
bad.  Also the zero node0_mem_free_bp parameter might look like a
reasonable setup to some users.  Hence, the issue might really happen in
the real world.

One reliable way to reproduce the issue is like below:

    # cd /sys/module/damon_sample_mtier/parameters
    # echo 4096 > node0_start_addr
    # echo 8192 > node0_end_addr
    # echo 8192 > node1_start_addr
    # echo 81920 > node1_end_addr
    # echo 0 > node0_mem_free_bp
    # echo Y > enabled
    # dmesg -w
    [...]
    [18792.235916] Oops: divide error: 0000 [#1] SMP NOPTI
    [...]
    [18792.242787] RIP: 0010:damos_quota_score+0x6f/0x480
    [...]

This issue was discovered [1] by Sashiko.

The Linux kernel CVE team has assigned CVE-2026-74643 to this issue.


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

	Issue introduced in 6.17 with commit c5e67d40a10234541e220750297304df79aaedd0 and fixed in 6.18.45 with commit e16b8d640ec99b28bc827560edcf9706e610c3aa
	Issue introduced in 6.17 with commit c5e67d40a10234541e220750297304df79aaedd0 and fixed in 7.1.9 with commit 684f271210becd7b8c4088f06c442499e48a43a0
	Issue introduced in 6.17 with commit c5e67d40a10234541e220750297304df79aaedd0 and fixed in 7.2 with commit a16fd3ad9d89b05475864da97327870464611736

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-2026-74643
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:
	samples/damon/mtier.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/e16b8d640ec99b28bc827560edcf9706e610c3aa
	https://git.kernel.org/stable/c/684f271210becd7b8c4088f06c442499e48a43a0
	https://git.kernel.org/stable/c/a16fd3ad9d89b05475864da97327870464611736