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ax25: Fix UAF bugs in ax25 timers

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There are race conditions that may lead to UAF bugs in
ax25_heartbeat_expiry(), ax25_t1timer_expiry(), ax25_t2timer_expiry(),
ax25_t3timer_expiry() and ax25_idletimer_expiry(), when we call
ax25_release() to deallocate ax25_dev.

One of the UAF bugs caused by ax25_release() is shown below:

      (Thread 1)                    |      (Thread 2)
ax25_dev_device_up() //(1)          |
...                                 | ax25_kill_by_device()
ax25_bind()          //(2)          |
ax25_connect()                      | ...
 ax25_std_establish_data_link()     |
  ax25_start_t1timer()              | ax25_dev_device_down() //(3)
   mod_timer(&ax25->t1timer,..)     |
                                    | ax25_release()
   (wait a time)                    |  ...
                                    |  ax25_dev_put(ax25_dev) //(4)FREE
   ax25_t1timer_expiry()            |
    ax25->ax25_dev->values[..] //USE|  ...
     ...                            |

We increase the refcount of ax25_dev in position (1) and (2), and
decrease the refcount of ax25_dev in position (3) and (4).
The ax25_dev will be freed in position (4) and be used in
ax25_t1timer_expiry().

The fail log is shown below:
==============================================================

[  106.116942] BUG: KASAN: use-after-free in ax25_t1timer_expiry+0x1c/0x60
[  106.116942] Read of size 8 at addr ffff88800bda9028 by task swapper/0/0
[  106.116942] CPU: 0 PID: 0 Comm: swapper/0 Not tainted 5.17.0-06123-g0905eec574
[  106.116942] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-14
[  106.116942] Call Trace:
...
[  106.116942]  ax25_t1timer_expiry+0x1c/0x60
[  106.116942]  call_timer_fn+0x122/0x3d0
[  106.116942]  __run_timers.part.0+0x3f6/0x520
[  106.116942]  run_timer_softirq+0x4f/0xb0
[  106.116942]  __do_softirq+0x1c2/0x651
...

This patch adds del_timer_sync() in ax25_release(), which could ensure
that all timers stop before we deallocate ax25_dev.

Signed-off-by: Duoming Zhou <duoming@zju.edu.cn>
Signed-off-by: Paolo Abeni <pabeni@redhat.com>
This commit is contained in:
Duoming Zhou 2022-03-28 21:00:15 +08:00 committed by Paolo Abeni
parent 5352a76130
commit 82e31755e5
1 changed files with 5 additions and 0 deletions
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5
net/ax25/af_ax25.c
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@ -1053,6 +1053,11 @@ static int ax25_release(struct socket *sock)
ax25_destroy_socket(ax25);
}
if (ax25_dev) {
del_timer_sync(&ax25->timer);
del_timer_sync(&ax25->t1timer);
del_timer_sync(&ax25->t2timer);
del_timer_sync(&ax25->t3timer);
del_timer_sync(&ax25->idletimer);
dev_put_track(ax25_dev->dev, &ax25_dev->dev_tracker);
ax25_dev_put(ax25_dev);
}