CVE-2024-56672

In the Linux kernel, the following vulnerability has been resolved:<br /> <br /> blk-cgroup: Fix UAF in blkcg_unpin_online()<br /> <br /> blkcg_unpin_online() walks up the blkcg hierarchy putting the online pin. To<br /> walk up, it uses blkcg_parent(blkcg) but it was calling that after<br /> blkcg_destroy_blkgs(blkcg) which could free the blkcg, leading to the<br /> following UAF:<br /> <br /> ==================================================================<br /> BUG: KASAN: slab-use-after-free in blkcg_unpin_online+0x15a/0x270<br /> Read of size 8 at addr ffff8881057678c0 by task kworker/9:1/117<br /> <br /> CPU: 9 UID: 0 PID: 117 Comm: kworker/9:1 Not tainted 6.13.0-rc1-work-00182-gb8f52214c61a-dirty #48<br /> Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS unknown 02/02/2022<br /> Workqueue: cgwb_release cgwb_release_workfn<br /> Call Trace:<br /> <br /> dump_stack_lvl+0x27/0x80<br /> print_report+0x151/0x710<br /> kasan_report+0xc0/0x100<br /> blkcg_unpin_online+0x15a/0x270<br /> cgwb_release_workfn+0x194/0x480<br /> process_scheduled_works+0x71b/0xe20<br /> worker_thread+0x82a/0xbd0<br /> kthread+0x242/0x2c0<br /> ret_from_fork+0x33/0x70<br /> ret_from_fork_asm+0x1a/0x30<br /> <br /> ...<br /> Freed by task 1944:<br /> kasan_save_track+0x2b/0x70<br /> kasan_save_free_info+0x3c/0x50<br /> __kasan_slab_free+0x33/0x50<br /> kfree+0x10c/0x330<br /> css_free_rwork_fn+0xe6/0xb30<br /> process_scheduled_works+0x71b/0xe20<br /> worker_thread+0x82a/0xbd0<br /> kthread+0x242/0x2c0<br /> ret_from_fork+0x33/0x70<br /> ret_from_fork_asm+0x1a/0x30<br /> <br /> Note that the UAF is not easy to trigger as the free path is indirected<br /> behind a couple RCU grace periods and a work item execution. I could only<br /> trigger it with artifical msleep() injected in blkcg_unpin_online().<br /> <br /> Fix it by reading the parent pointer before destroying the blkcg&amp;#39;s blkg&amp;#39;s.