About vulnerability

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.

Affected product:

Debian 10 ELS

Affected packages:

linux @ 4.19.0