dm thin: Fix UAF in run_timer_softirq()
CVE: CVE-2022-50563
Component: kernel
CWE: CWE-416
Severity: Moderate
CVSS v3: 5.1/AV:L/AC:L/PR:H/UI:N/S:U/C:N/I:N/A:H
Release date: 2022-01-01T00:00:00+00:00

In the Linux kernel, the following vulnerability has been resolved:

dm thin: Fix UAF in run_timer_softirq()

When dm_resume() and dm_destroy() are concurrent, it will
lead to UAF, as follows:

 BUG: KASAN: use-after-free in __run_timers+0x173/0x710
 Write of size 8 at addr ffff88816d9490f0 by task swapper/0/0
<snip>
 Call Trace:
  <IRQ>
  dump_stack_lvl+0x73/0x9f
  print_report.cold+0x132/0xaa2
  _raw_spin_lock_irqsave+0xcd/0x160
  __run_timers+0x173/0x710
  kasan_report+0xad/0x110
  __run_timers+0x173/0x710
  __asan_store8+0x9c/0x140
  __run_timers+0x173/0x710
  call_timer_fn+0x310/0x310
  pvclock_clocksource_read+0xfa/0x250
  kvm_clock_read+0x2c/0x70
  kvm_clock_get_cycles+0xd/0x20
  ktime_get+0x5c/0x110
  lapic_next_event+0x38/0x50
  clockevents_program_event+0xf1/0x1e0
  run_timer_softirq+0x49/0x90
  __do_softirq+0x16e/0x62c
  __irq_exit_rcu+0x1fa/0x270
  irq_exit_rcu+0x12/0x20
  sysvec_apic_timer_interrupt+0x8e/0xc0

One of the concurrency UAF can be shown as below:

        use                                  free
do_resume                           |
  __find_device_hash_cell           |
    dm_get                          |
      atomic_inc(&md->holders)      |
                                    | dm_destroy
                                    |   __dm_destroy
                                    |     if (!dm_suspended_md(md))
                                    |     atomic_read(&md->holders)
                                    |     msleep(1)
  dm_resume                         |
    __dm_resume                     |
      dm_table_resume_targets       |
        pool_resume                 |
          do_waker  #add delay work |
  dm_put                            |
    atomic_dec(&md->holders)        |
                                    |     dm_table_destroy
                                    |       pool_dtr
                                    |         __pool_dec
                                    |           __pool_destroy
                                    |             destroy_workqueue
                                    |             kfree(pool) # free pool
        time out
__do_softirq
  run_timer_softirq # pool has already been freed

This can be easily reproduced using:
  1. create thin-pool
  2. dmsetup suspend pool
  3. dmsetup resume pool
  4. dmsetup remove_all # Concurrent with 3

The root cause of this UAF bug is that dm_resume() adds timer after
dm_destroy() skips cancelling the timer because of suspend status.
After timeout, it will call run_timer_softirq(), however pool has
already been freed. The concurrency UAF bug will happen.

Therefore, cancelling timer again in __pool_destroy().

Statement: Fixes a use-after-free in device-mapper thin-provisioning where delayed works (waker, no_space_timeout) could still fire after a pool is freed during a concurrent dm_resume()/dm_destroy() sequence, leading to UAF in run_timer_softirq() and a kernel crash. Exploitation requires root/DM control (e.g., racing dmsetup resume with dmsetup remove), so the practical risk is local DoS during pool teardown rather than data exfiltration. For the CVSS the PR:H since triggering it needs high-privilege block-stack operations.

Remediation:
For details on how to apply this update, which includes the changes described in this advisory, refer to:

https://access.redhat.com/articles/11258

The system must be rebooted for this update to take effect.
For details on how to apply this update, which includes the changes described in this advisory, refer to:

https://access.redhat.com/articles/11258

The system must be rebooted for this update to take effect.