linux-cve-announce - CVE-2024-56672: blk-cgroup: Fix UAF in blkcg_unpin

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Message-ID: <2024122755-CVE-2024-56672-8d29@gregkh>
Date: Fri, 27 Dec 2024 16:07:09 +0100
From: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To: linux-cve-announce@...r.kernel.org
Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Subject: CVE-2024-56672: blk-cgroup: Fix UAF in blkcg_unpin_online()

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.

The Linux kernel CVE team has assigned CVE-2024-56672 to this issue.

Affected and fixed versions
===========================

	Issue introduced in 5.7 with commit 4308a434e5e08c78676aa66bc626ef78cbef0883 and fixed in 6.1.121 with commit 64afc6fe24c9896c0153e5a199bcea241ecb0d5c
	Issue introduced in 5.7 with commit 4308a434e5e08c78676aa66bc626ef78cbef0883 and fixed in 6.6.67 with commit 5baa28569c924d9a90d036c2aaab79f791fedaf8
	Issue introduced in 5.7 with commit 4308a434e5e08c78676aa66bc626ef78cbef0883 and fixed in 6.12.6 with commit 29d1e06560f0f6179062ac638b4064deb637d1ad
	Issue introduced in 5.7 with commit 4308a434e5e08c78676aa66bc626ef78cbef0883 and fixed in 6.13-rc3 with commit 86e6ca55b83c575ab0f2e105cf08f98e58d3d7af

Please see https://www.kernel.org for a full list of currently supported
kernel versions by the kernel community.

Unaffected versions might change over time as fixes are backported to
older supported kernel versions.  The official CVE entry at
	https://cve.org/CVERecord/?id=CVE-2024-56672
will be updated if fixes are backported, please check that for the most
up to date information about this issue.

Affected files
==============

The file(s) affected by this issue are:
	block/blk-cgroup.c

Mitigation
==========

The Linux kernel CVE team recommends that you update to the latest
stable kernel version for this, and many other bugfixes.  Individual
changes are never tested alone, but rather are part of a larger kernel
release.  Cherry-picking individual commits is not recommended or
supported by the Linux kernel community at all.  If however, updating to
the latest release is impossible, the individual changes to resolve this
issue can be found at these commits:
	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