[v2,1/4] dm thin: Fix UAF in run_timer_softirq()

Commit Message

Luo Meng Nov. 29, 2022, 2:48 a.m. UTC

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

 CPU: 0 PID: 0 Comm: swapper/0 Not tainted 6.0.0-rc6-00001-gaed496328fcd-dirty #26
 Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS ?-20190727_073836-buildvm-ppc64le-16.ppc.fedoraproject.org-3.fc31 04/01/2014
 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 UAF bugs is that dm_resume() adds timer after
dm_destroy() skips cancel timer beause of suspend status. After
timeout, it will call run_timer_softirq(), however pool has already
been freed. The concurrency UAF bug will happen.

Therefore, canceling timer again in __pool_destroy().

Fixes: 991d9fa02da0d (dm: add thin provisioning target)
Signed-off-by: Luo Meng <[e-mail]>
---
 drivers/md/dm-thin.c | 2 ++
 1 file changed, 2 insertions(+)

Patch

diff --git a/drivers/md/dm-thin.c b/drivers/md/dm-thin.c
index e76c96c760a9..dc271c107fb5 100644
--- a/drivers/md/dm-thin.c
+++ b/drivers/md/dm-thin.c
@@ -2889,6 +2889,8 @@  static void __pool_destroy(struct pool *pool)
 	dm_bio_prison_destroy(pool->prison);
 	dm_kcopyd_client_destroy(pool->copier);
 
+	cancel_delayed_work_sync(&pool->waker);
+	cancel_delayed_work_sync(&pool->no_space_timeout);
 	if (pool->wq)
 		destroy_workqueue(pool->wq);