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ax25: fix UAF bugs of net_device caused by rebinding operation

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The ax25_kill_by_device() will set s->ax25_dev = NULL and
call ax25_disconnect() to change states of ax25_cb and
sock, if we call ax25_bind() before ax25_kill_by_device().

However, if we call ax25_bind() again between the window of
ax25_kill_by_device() and ax25_dev_device_down(), the values
and states changed by ax25_kill_by_device() will be reassigned.

Finally, ax25_dev_device_down() will deallocate net_device.
If we dereference net_device in syscall functions such as
ax25_release(), ax25_sendmsg(), ax25_getsockopt(), ax25_getname()
and ax25_info_show(), a UAF bug will occur.

One of the possible race conditions is shown below:

      (USE)                   |      (FREE)
ax25_bind()                   |
                              |  ax25_kill_by_device()
ax25_bind()                   |
ax25_connect()                |    ...
                              |  ax25_dev_device_down()
                              |    ...
                              |    dev_put_track(dev, ...) //FREE
ax25_release()                |    ...
  ax25_send_control()         |
    alloc_skb()      //USE    |

the corresponding fail log is shown below:
===============================================================
BUG: KASAN: use-after-free in ax25_send_control+0x43/0x210
...
Call Trace:
  ...
  ax25_send_control+0x43/0x210
  ax25_release+0x2db/0x3b0
  __sock_release+0x6d/0x120
  sock_close+0xf/0x20
  __fput+0x11f/0x420
  ...
Allocated by task 1283:
  ...
  __kasan_kmalloc+0x81/0xa0
  alloc_netdev_mqs+0x5a/0x680
  mkiss_open+0x6c/0x380
  tty_ldisc_open+0x55/0x90
  ...
Freed by task 1969:
  ...
  kfree+0xa3/0x2c0
  device_release+0x54/0xe0
  kobject_put+0xa5/0x120
  tty_ldisc_kill+0x3e/0x80
  ...

In order to fix these UAF bugs caused by rebinding operation,
this patch adds dev_hold_track() into ax25_bind() and
corresponding dev_put_track() into ax25_kill_by_device().

Signed-off-by: Duoming Zhou <duoming@zju.edu.cn>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Duoming Zhou 2022-02-09 20:53:45 +08:00 committed by David S. Miller
parent ee534378f0
commit feef318c85
1 changed files with 4 additions and 1 deletions
repo.diff.show_diff_stats Download patch file Download diff file Expand all files Collapse all files

5
net/ax25/af_ax25.c
View file

@ -91,6 +91,7 @@ static void ax25_kill_by_device(struct net_device *dev)
spin_unlock_bh(&ax25_list_lock); spin_unlock_bh(&ax25_list_lock);
lock_sock(sk); lock_sock(sk);
s->ax25_dev = NULL; s->ax25_dev = NULL;
dev_put_track(ax25_dev->dev, &ax25_dev->dev_tracker);
ax25_dev_put(ax25_dev); ax25_dev_put(ax25_dev);
ax25_disconnect(s, ENETUNREACH); ax25_disconnect(s, ENETUNREACH);
release_sock(sk); release_sock(sk);
@ -1116,8 +1117,10 @@ static int ax25_bind(struct socket *sock, struct sockaddr *uaddr, int addr_len)
} }
} }
if (ax25_dev != NULL) if (ax25_dev) {
ax25_fillin_cb(ax25, ax25_dev); ax25_fillin_cb(ax25, ax25_dev);
dev_hold_track(ax25_dev->dev, &ax25_dev->dev_tracker, GFP_ATOMIC);
}
done: done:
ax25_cb_add(ax25); ax25_cb_add(ax25);