CVE-2026-90326blk-cgroup: fix race between policy activation and blkg destruction

Official description

In the Linux kernel, the following vulnerability has been resolved: blk-cgroup: fix race between policy activation and blkg destruction When switching an IO scheduler on a block device, blkcg_activate_policy() allocates blkg_policy_data (pd) for all blkgs attached to the queue. However, blkcg_activate_policy() may race with concurrent blkcg deletion, leading to use-after-free and memory leak issues. The use-after-free occurs in the following race: T1 (blkcg_activate_policy): - Successfully allocates pd for blkg1 (loop0->queue, blkcgA) - Fails to allocate pd for blkg2 (loop0->queue, blkcgB) - Enters the enomem rollback path to release blkg1 resources T2 (blkcg deletion): - blkcgA is deleted concurrently - blkg1 is freed via blkg_free_workfn() - blkg1->pd is freed T1 (continued): - Rollback path accesses blkg1->pd->online after pd is freed - Triggers use-after-free In addition, blkg_free_workfn() frees pd before removing the blkg from q->blkg_list. This allows blkcg_activate_policy() to allocate a new pd for a blkg that is being destroyed, leaving the newly allocated pd unreachable when the blkg is finally freed. Fix these races by extending blkcg_mutex coverage to serialize blkcg_activate_policy() rollback and blkg destruction, ensuring pd lifecycle is synchronized with blkg list visibility.

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/17c18a0df70c2b89ff7fcd74622f1540e98d00fd
• https://git.kernel.org/stable/c/91062e3a9ed251726df4e20ff9a1113f1c8ded59
• https://git.kernel.org/stable/c/ac34e655dffa74349d885a43d098115336f53842
• https://git.kernel.org/stable/c/2cf9f50a38c1839e549a08e22aa35e8d69e2c8fd
• https://git.kernel.org/stable/c/5313d4d41739b0cb63000747c97bb1217ac45f3e