[PATCH 1/1] blk-cgroup: Fix UAF in blkcg_unpin_online()

[PATCH 1/1] blk-cgroup: Fix UAF in blkcg_unpin_online()

[ciprietti]

From: Tejun Heo <tj@kernel.org>

[ Upstream commit 86e6ca55b83c575ab0f2e105cf08f98e58d3d7af ]

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>
Signed-off-by: Andrea Ciprietti <ciprietti@google.com>
---
 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 0e6e84db06f6..b89099360a86 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);
 }
 
-- 
2.48.1.262.g85cc9f2d1e-goog

Re: [PATCH 1/1] blk-cgroup: Fix UAF in blkcg_unpin_online()

[Andrea Ciprietti]

Hi, this is a version of commit 86e6ca55b83c ("blk-cgroup: Fix UAF in
blkcg_unpin_online()") adapted for porting to the 5.10 LTS tree.

The patch fixes CVE-2024-56672.

Changes with respect to the original commit:
  - blkcg_unpin_online() is implemented in linux/blk-cgroup.h.

Thanks,
Andrea

Re: [PATCH 1/1] blk-cgroup: Fix UAF in blkcg_unpin_online()

[Greg KH]

On Wed, Jan 29, 2025 at 04:43:25PM +0000, Andrea Ciprietti wrote:
> Hi, this is a version of commit 86e6ca55b83c ("blk-cgroup: Fix UAF in
> blkcg_unpin_online()") adapted for porting to the 5.10 LTS tree.
> 
> The patch fixes CVE-2024-56672.
> 
> Changes with respect to the original commit:
>   - blkcg_unpin_online() is implemented in linux/blk-cgroup.h.

This is already in the 5.10.y queue, but NOT in the 5.15.y queue at all.
Can you do this for 5.15.y instead?

thanks,

greg k-h

Re: [PATCH 1/1] blk-cgroup: Fix UAF in blkcg_unpin_online()

[Andrea Ciprietti]

Hi Greg,

My apologies, I didn't notice that the patch was already queued for 5.10.y. 
As for 5.15.y, it should be already merged as commit 8a07350fe070 in the 
stable repo: 
https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=8a07350fe070. 
Same goes for the other LTS trees up to 6.13.y.

If that sounds right to you, I believe there is nothing left to do here.

Thanks,
Andrea

Re: [PATCH 1/1] blk-cgroup: Fix UAF in blkcg_unpin_online()

[Greg KH]

On Thu, Jan 30, 2025 at 10:38:12AM +0000, Andrea Ciprietti wrote:
> Hi Greg,
> 
> My apologies, I didn't notice that the patch was already queued for 5.10.y. 
> As for 5.15.y, it should be already merged as commit 8a07350fe070 in the 
> stable repo: 
> https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=8a07350fe070. 
> Same goes for the other LTS trees up to 6.13.y.

Oops, yes, I missed it in 5.15.y already, sorry.

lots of missing in this thread, we all need more coffee...

thanks!

greg k-h

Re: [PATCH 1/1] blk-cgroup: Fix UAF in blkcg_unpin_online()

[Sasha Levin]

[ Sasha's backport helper bot ]

Hi,

The upstream commit SHA1 provided is correct: 86e6ca55b83c575ab0f2e105cf08f98e58d3d7af

WARNING: Author mismatch between patch and upstream commit:
Backport author: ciprietti@google.com
Commit author: Tejun Heo<tj@kernel.org>


Status in newer kernel trees:
6.13.y | Present (exact SHA1)

Note: The patch differs from the upstream commit:
---
Failed to apply patch cleanly, falling back to interdiff...
---

Results of testing on various branches:

| Branch                    | Patch Apply | Build Test |
|---------------------------|-------------|------------|
| stable/linux-6.13.y       |  Failed     |  N/A       |
| stable/linux-6.12.y       |  Failed     |  N/A       |
| stable/linux-6.6.y        |  Failed     |  N/A       |
| stable/linux-6.1.y        |  Failed     |  N/A       |
| stable/linux-5.15.y       |  Failed     |  N/A       |
| stable/linux-5.10.y       |  Success    |  Success   |
| stable/linux-5.4.y        |  Failed     |  N/A       |