CVE-2024-56672: blk-cgroup: Fix UAF in blkcg_unpin_online()
First published: Fri Dec 27 2024(Updated: )
In the Linux kernel, the following vulnerability has been resolved: blk-cgroup: Fix UAF in blkcg_unpin_online() blkcg_unpin_online() walks up the blkcg hierarchy putting the online pin. To walk up, it uses blkcg_parent(blkcg) but it was calling that after blkcg_destroy_blkgs(blkcg) which could free the blkcg, leading to the following UAF: ================================================================== BUG: KASAN: slab-use-after-free in blkcg_unpin_online+0x15a/0x270 Read of size 8 at addr ffff8881057678c0 by task kworker/9:1/117 CPU: 9 UID: 0 PID: 117 Comm: kworker/9:1 Not tainted 6.13.0-rc1-work-00182-gb8f52214c61a-dirty #48 Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS unknown 02/02/2022 Workqueue: cgwb_release cgwb_release_workfn Call Trace: <TASK> dump_stack_lvl+0x27/0x80 print_report+0x151/0x710 kasan_report+0xc0/0x100 blkcg_unpin_online+0x15a/0x270 cgwb_release_workfn+0x194/0x480 process_scheduled_works+0x71b/0xe20 worker_thread+0x82a/0xbd0 kthread+0x242/0x2c0 ret_from_fork+0x33/0x70 ret_from_fork_asm+0x1a/0x30 </TASK> ... Freed by task 1944: kasan_save_track+0x2b/0x70 kasan_save_free_info+0x3c/0x50 __kasan_slab_free+0x33/0x50 kfree+0x10c/0x330 css_free_rwork_fn+0xe6/0xb30 process_scheduled_works+0x71b/0xe20 worker_thread+0x82a/0xbd0 kthread+0x242/0x2c0 ret_from_fork+0x33/0x70 ret_from_fork_asm+0x1a/0x30 Note that the UAF is not easy to trigger as the free path is indirected behind a couple RCU grace periods and a work item execution. I could only trigger it with artifical msleep() injected in blkcg_unpin_online(). Fix it by reading the parent pointer before destroying the blkcg's blkg's.
Credit: 416baaa9-dc9f-4396-8d5f-8c081fb06d67
| Affected Software | Affected Version | How to fix |
|---|---|---|
| >=5.7<6.1.121 | ||
| >=6.2<6.6.67 | ||
| >=6.7<6.12.6 | ||
| =6.13-rc1 | ||
| =6.13-rc2 |
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Reference Links
- https://git.kernel.org/stable/c/83f5a87ee8caa76a917f59912a74d6811f773c67
- https://git.kernel.org/stable/c/8a07350fe070017a887433f4d6909433955be5f1
- https://git.kernel.org/stable/c/64afc6fe24c9896c0153e5a199bcea241ecb0d5c
- https://git.kernel.org/stable/c/5baa28569c924d9a90d036c2aaab79f791fedaf8
- https://git.kernel.org/stable/c/29d1e06560f0f6179062ac638b4064deb637d1ad
- https://git.kernel.org/stable/c/86e6ca55b83c575ab0f2e105cf08f98e58d3d7af
Frequently Asked Questions
What is the severity of CVE-2024-56672?
CVE-2024-56672 has been rated with a high severity level due to its potential to cause use-after-free issues in the Linux kernel.
How do I fix CVE-2024-56672?
To fix CVE-2024-56672, you should upgrade your Linux kernel to a version that includes the relevant patches addressing this vulnerability.
Which Linux kernel versions are affected by CVE-2024-56672?
CVE-2024-56672 affects Linux kernel versions between 5.7 and 6.1.121, and also versions between 6.2 and 6.6.67, as well as 6.7 to 6.12.6.
What is the impact of CVE-2024-56672 on system security?
The impact of CVE-2024-56672 can lead to memory corruption and potentially allow an attacker to execute arbitrary code in kernel mode.
Is CVE-2024-56672 a remote or local vulnerability?
CVE-2024-56672 is primarily considered a local vulnerability since it requires elevated privileges to exploit.
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