CVE-2026-64239

01/Description

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.

02/Affected products

linux: linux kernel

03/References5

• git.kernel.org/stable/c/0ba6c05156d9ff9fc6ca22b7690e2eec9eca66f7 Patch
• git.kernel.org/stable/c/2c33177023c92e76806c535ddbffaa3d3fc37777 Patch
• git.kernel.org/stable/c/441f92f7d386b85bad16de49db95a307cba048a2 Patch
• git.kernel.org/stable/c/a5fa42214de55e43d165144727ce9facb9fc6b08 Patch
• git.kernel.org/stable/c/c0e37017a452addec873865c94cf7a665663a9b2 Patch