PT-2026-64354 · Linux · Linux
CVE-2026-64239
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Publicado
2026-07-24
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Atualizado
2026-07-24
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In the Linux kernel, the following vulnerability has been resolved:
mm/damon/sysfs-schemes: delete tried region in regions rmdirs()
DAMON sysfs maintains the DAMOS tried region directory objects via a
linked list. When the user requests refresh of the directories, DAMON
sysfs removes all the region directories first, and then generate updated
regions directory on the empty space. The removal function
(damon sysfs scheme regions rm dirs()) only puts the kobj objects.
Deletion of the container region object from the linked list is done
inside the kobj release callback function.
If somehow the callback invocation is delayed, the list will contain
regions list that gonna be freed. If the updated region directories
creation is started in this situation, the list can be corrupted and
use-after-free can happen.
Because the kobj objects are managed by only DAMON sysfs, the issue cannot
happen in normal situation. But, such delays can be made on kernels that
built with CONFIG DEBUG KOBJECT RELEASE. On the kernel, the issue can
indeed be reproduced like below.
damo start --damos action stat
cd /sys/kernel/mm/damon/admin/kdamonds/0/
for i in {1..10}; do echo update schemes tried regions > state; done
dmesg | grep underflow
[ 89.296152] refcount t: underflow; use-after-free.
Fix the issue by removing the region object from the list when
decrementing the reference count.
Also update damos sysfs populate region dir() to add the region object to
the list only after the kobject init and add() is success, so that fail of
kobject init and add() is not leaving the deallocated object on the list.
The issue was discovered [1] by Sashiko.
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