From: Tejun Heo tj@kernel.org
commit 86e6ca55b83c575ab0f2e105cf08f98e58d3d7af upstream.
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.
Signed-off-by: Tejun Heo tj@kernel.org Reported-by: Abagail ren renzezhongucas@gmail.com Suggested-by: Linus Torvalds torvalds@linuxfoundation.org Fixes: 4308a434e5e0 ("blkcg: don't offline parent blkcg first") Cc: stable@vger.kernel.org # v5.7+ Signed-off-by: Jens Axboe axboe@kernel.dk [kovalev: in versions 5.10 and 5.15, the blkcg_unpin_online() function was not moved to the block/blk-cgroup.c file] Signed-off-by: Vasiliy Kovalev kovalev@altlinux.org --- Backport to fix CVE-2024-56672 Link: https://www.cve.org/CVERecord/?id=CVE-2024-56672 --- include/linux/blk-cgroup.h | 6 +++++- 1 file changed, 5 insertions(+), 1 deletion(-)
diff --git a/include/linux/blk-cgroup.h b/include/linux/blk-cgroup.h index 0e6e84db06f674..b89099360a8673 100644 --- a/include/linux/blk-cgroup.h +++ b/include/linux/blk-cgroup.h @@ -428,10 +428,14 @@ static inline void blkcg_pin_online(struct blkcg *blkcg) static inline void blkcg_unpin_online(struct blkcg *blkcg) { do { + struct blkcg *parent; + if (!refcount_dec_and_test(&blkcg->online_pin)) break; + + parent = blkcg_parent(blkcg); blkcg_destroy_blkgs(blkcg); - blkcg = blkcg_parent(blkcg); + blkcg = parent; } while (blkcg); }
[ Sasha's backport helper bot ]
Hi,
The upstream commit SHA1 provided is correct: 86e6ca55b83c575ab0f2e105cf08f98e58d3d7af
WARNING: Author mismatch between patch and upstream commit: Backport author: Vasiliy Kovalevkovalev@altlinux.org Commit author: Tejun Heotj@kernel.org
Status in newer kernel trees: 6.12.y | Present (different SHA1: 29d1e06560f0) 6.6.y | Present (different SHA1: 5baa28569c92) 6.1.y | Present (different SHA1: 64afc6fe24c9) 5.15.y | Not found
Note: The patch differs from the upstream commit: --- 1: 86e6ca55b83c ! 1: 4a53d2caa691 blk-cgroup: Fix UAF in blkcg_unpin_online() @@ Metadata ## Commit message ## blk-cgroup: Fix UAF in blkcg_unpin_online()
+ commit 86e6ca55b83c575ab0f2e105cf08f98e58d3d7af upstream. + 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 @@ Commit message Fixes: 4308a434e5e0 ("blkcg: don't offline parent blkcg first") Cc: stable@vger.kernel.org # v5.7+ Signed-off-by: Jens Axboe axboe@kernel.dk + [kovalev: in versions 5.10 and 5.15, the blkcg_unpin_online() + function was not moved to the block/blk-cgroup.c file] + Signed-off-by: Vasiliy Kovalev kovalev@altlinux.org
- ## block/blk-cgroup.c ## -@@ block/blk-cgroup.c: void blkcg_unpin_online(struct cgroup_subsys_state *blkcg_css) - struct blkcg *blkcg = css_to_blkcg(blkcg_css); - + ## include/linux/blk-cgroup.h ## +@@ include/linux/blk-cgroup.h: static inline void blkcg_pin_online(struct blkcg *blkcg) + static inline void blkcg_unpin_online(struct blkcg *blkcg) + { do { + struct blkcg *parent; + ---
Results of testing on various branches:
| Branch | Patch Apply | Build Test | |---------------------------|-------------|------------| | stable/linux-5.15.y | Success | Success | | stable/linux-5.10.y | Success | Success |
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