Abagail Ren

**Name of the Vulnerable Software and Affected Versions** Linux kernel versions prior to 6.6.74 **Description** The issue is related to a Use-After-Free (UAF) vulnerability in the `blkcg unpin online()` function in the Linux kernel's block control group (blk-cgroup) subsystem. The vulnerability occurs when the `blkcg unpin online()` function walks up the blkcg hierarchy, putting the online pin, and uses `blkcg parent(blkcg)` after `blkcg destroy blkgs(blkcg)`, which could free the blkcg, leading to a UAF. The UAF is not easy to trigger as the free path is indirected behind a couple RCU grace periods and a work item execution. **Recommendations** To resolve the issue, update the Linux kernel to version 6.6.74 or later. As a temporary workaround, consider restricting access to the vulnerable `blkcg unpin online()` function until a patch is available. Note that the UAF is not easy to trigger, but updating the kernel to a fixed version is still recommended to ensure the security of the system.