CVE-2026-64239 is a vulnerability in Linux Kernel
Published on July 24, 2026
mm/damon/sysfs-schemes: delete tried region in regions_rmdirs()
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.
Products Associated with CVE-2026-64239
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Affected Versions
Linux:- Version 9277d0367ba18ef4bb98bafb1209e715844cdf7e and below c0e37017a452addec873865c94cf7a665663a9b2 is affected.
- Version 9277d0367ba18ef4bb98bafb1209e715844cdf7e and below a5fa42214de55e43d165144727ce9facb9fc6b08 is affected.
- Version 9277d0367ba18ef4bb98bafb1209e715844cdf7e and below 0ba6c05156d9ff9fc6ca22b7690e2eec9eca66f7 is affected.
- Version 9277d0367ba18ef4bb98bafb1209e715844cdf7e and below 2c33177023c92e76806c535ddbffaa3d3fc37777 is affected.
- Version 9277d0367ba18ef4bb98bafb1209e715844cdf7e and below 441f92f7d386b85bad16de49db95a307cba048a2 is affected.
- Version 6.2 is affected.
- Before 6.2 is unaffected.
- Version 6.6.143, <= 6.6.* is unaffected.
- Version 6.12.93, <= 6.12.* is unaffected.
- Version 6.18.35, <= 6.18.* is unaffected.
- Version 7.0.12, <= 7.0.* is unaffected.
- Version 7.1, <= * is unaffected.