Entreprise française de cybersécurité depuis 2004
☎ 03 60 47 09 81 - info@securiteinfo.com

CVE-2024-56672

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. Towalk up, it uses blkcg_parent(blkcg) but it was calling that afterblkcg_destroy_blkgs(blkcg) which could free the blkcg, leading to thefollowing 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: 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 ... 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/0x30Note that the UAF is not easy to trigger as the free path is indirectedbehind a couple RCU grace periods and a work item execution. I could onlytrigger it with artifical msleep() injected in blkcg_unpin_online().Fix it by reading the parent pointer before destroying the blkcg's blkg's.

POC

Reference

No PoCs from references.

Github

- https://github.com/cku-heise/euvd-api-doc

- https://github.com/w4zu/Debian_security