CVE-2026-74643

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 damosquotascore()".

DAMONSAMPLEMTIER and DAMONLRUSORT allow the user to trigger division by zero in damosquotascore(). Avoid it by adding parameters validation checks.

This patch (of 2):

damosquotascore() can trigger division by zero if the targetvalue is zero. DAMONSAMPLEMTIER lets users set the targetvalue via node0mem{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 node0mem_{used,free}_bp parameter values.

DAMONSAMPLEMTIER is just a sample module, but the consequence is quite bad. Also the zero node0memfree_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.