CVE-2024-56672

blk-cgroup: Fix UAF in blkcg_unpin_online()

State: Published
Severity: 7.8 High
Published: Dec 27, 2024
Updated: Oct 15, 2026
Reserved: Dec 27, 2024

Description

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.

Scores

CVSS	Score	Vector	Source
3.1	7.8 High	CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H	Linux
3.1	7.8 High	CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H	CISA-ADP

Weaknesses

CWE-416 Use After Free

Affected Products

Product	Versions
LinuxLinux	4308a434e5e08c78676aa66bc626ef78cbef0883 to before 83f5a87ee8caa76a917f59912a74d6811f773c67Affected 4308a434e5e08c78676aa66bc626ef78cbef0883 to before 8a07350fe070017a887433f4d6909433955be5f1Affected 4308a434e5e08c78676aa66bc626ef78cbef0883 to before 64afc6fe24c9896c0153e5a199bcea241ecb0d5cAffected 4308a434e5e08c78676aa66bc626ef78cbef0883 to before 5baa28569c924d9a90d036c2aaab79f791fedaf8Affected 4308a434e5e08c78676aa66bc626ef78cbef0883 to before 29d1e06560f0f6179062ac638b4064deb637d1adAffected 4308a434e5e08c78676aa66bc626ef78cbef0883 to before 86e6ca55b83c575ab0f2e105cf08f98e58d3d7afAffected
LinuxLinux	5.7Affected before 5.7Not affected 5.10.234 through 5.10.Not affected 5.15.177 through 5.15.Not affected 6.1.121 through 6.1.Not affected 6.6.67 through 6.6.Not affected 6.12.6 through 6.12.*Not affected 6.13 and laterNot affected

Product

Versions

LinuxLinux

4308a434e5e08c78676aa66bc626ef78cbef0883 to before 83f5a87ee8caa76a917f59912a74d6811f773c67Affected
4308a434e5e08c78676aa66bc626ef78cbef0883 to before 8a07350fe070017a887433f4d6909433955be5f1Affected
4308a434e5e08c78676aa66bc626ef78cbef0883 to before 64afc6fe24c9896c0153e5a199bcea241ecb0d5cAffected
4308a434e5e08c78676aa66bc626ef78cbef0883 to before 5baa28569c924d9a90d036c2aaab79f791fedaf8Affected
4308a434e5e08c78676aa66bc626ef78cbef0883 to before 29d1e06560f0f6179062ac638b4064deb637d1adAffected
4308a434e5e08c78676aa66bc626ef78cbef0883 to before 86e6ca55b83c575ab0f2e105cf08f98e58d3d7afAffected

LinuxLinux

5.7Affected
before 5.7Not affected
5.10.234 through 5.10.*Not affected
5.15.177 through 5.15.*Not affected
6.1.121 through 6.1.*Not affected
6.6.67 through 6.6.*Not affected
6.12.6 through 6.12.*Not affected
6.13 and laterNot affected

References

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