CVE-2026-90325blk-cgroup: skip dying blkg in blkcg_activate_policy()

Official description

In the Linux kernel, the following vulnerability has been resolved: blk-cgroup: skip dying blkg in blkcg_activate_policy() When switching IO schedulers on a block device, blkcg_activate_policy() can race with concurrent blkcg deletion, leading to a use-after-free in rcu_accelerate_cbs. T1: T2: blkg_destroy kill(&blkg->refcnt) // blkg->refcnt=1->0 blkg_release // call_rcu(__blkg_release) ... blkg_free_workfn ->pd_free_fn(pd) elv_iosched_store elevator_switch ... iterate blkg list blkg_get(blkg) // blkg->refcnt=0->1 list_del_init(&blkg->q_node) blkg_put(pinned_blkg) // blkg->refcnt=1->0 blkg_release // call_rcu again rcu_accelerate_cbs // uaf Fix this by checking hlist_unhashed(&blkg->blkcg_node) before getting a reference to the blkg. This is the same check used in blkg_destroy() to detect if a blkg has already been destroyed. If the blkg is already unhashed, skip processing it since it's being destroyed.

Affected packages & fixed versions

Affected products (as reported)

References

• https://git.kernel.org/stable/c/b5dae1cd0d8368b4338430ff93403df67f0b8bcc
• https://git.kernel.org/stable/c/083b58373463a6e5ee60ecb135269348f68ad7df
• https://git.kernel.org/stable/c/1a267295b1ea6a6477963f3fda84adfecd48fcad
• https://git.kernel.org/stable/c/7337d012ca3fc3a6a2d1c8e2a19c6d97c38b410d
• https://git.kernel.org/stable/c/3d8c3da95c75a4d312e272fc7b4076dd3ba9115c
• https://git.kernel.org/stable/c/d8c872901e6459339374e9eea80aa919176c2ccd
• https://git.kernel.org/stable/c/5e9220389920f33b6a804d50c548cd0cd1b04634