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ax25: Fix refcount leaks caused by ax25_cb_del()

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The previous commit d01ffb9eee ("ax25: add refcount in ax25_dev to
avoid UAF bugs") and commit feef318c85 ("ax25: fix UAF bugs of
net_device caused by rebinding operation") increase the refcounts of
ax25_dev and net_device in ax25_bind() and decrease the matching refcounts
in ax25_kill_by_device() in order to prevent UAF bugs, but there are
reference count leaks.

The root cause of refcount leaks is shown below:

     (Thread 1)                      |      (Thread 2)
ax25_bind()                          |
 ...                                 |
 ax25_addr_ax25dev()                 |
  ax25_dev_hold()   //(1)            |
  ...                                |
 dev_hold_track()   //(2)            |
 ...                                 | ax25_destroy_socket()
                                     |  ax25_cb_del()
                                     |   ...
                                     |   hlist_del_init() //(3)
                                     |
                                     |
     (Thread 3)                      |
ax25_kill_by_device()                |
 ...                                 |
 ax25_for_each(s, &ax25_list) {      |
  if (s->ax25_dev == ax25_dev) //(4) |
   ...                               |

Firstly, we use ax25_bind() to increase the refcount of ax25_dev in
position (1) and increase the refcount of net_device in position (2).
Then, we use ax25_cb_del() invoked by ax25_destroy_socket() to delete
ax25_cb in hlist in position (3) before calling ax25_kill_by_device().
Finally, the decrements of refcounts in ax25_kill_by_device() will not
be executed, because no s->ax25_dev equals to ax25_dev in position (4).

This patch adds decrements of refcounts in ax25_release() and use
lock_sock() to do synchronization. If refcounts decrease in ax25_release(),
the decrements of refcounts in ax25_kill_by_device() will not be
executed and vice versa.

Fixes: d01ffb9eee ("ax25: add refcount in ax25_dev to avoid UAF bugs")
Fixes: 87563a043c ("ax25: fix reference count leaks of ax25_dev")
Fixes: feef318c85 ("ax25: fix UAF bugs of net_device caused by rebinding operation")
Reported-by: Thomas Osterried <thomas@osterried.de>
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 2022-03-18 08:54:04 +08:00 committed by David S. Miller
parent 0caf6d9922
commit 9fd75b66b8
1 changed files with 11 additions and 3 deletions
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14
net/ax25/af_ax25.c
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@ -98,8 +98,10 @@ again:
spin_unlock_bh(&ax25_list_lock);
lock_sock(sk);
s->ax25_dev = NULL;
dev_put_track(ax25_dev->dev, &ax25_dev->dev_tracker);
ax25_dev_put(ax25_dev);
if (sk->sk_socket) {
dev_put_track(ax25_dev->dev, &ax25_dev->dev_tracker);
ax25_dev_put(ax25_dev);
}
ax25_disconnect(s, ENETUNREACH);
release_sock(sk);
spin_lock_bh(&ax25_list_lock);
@ -979,14 +981,20 @@ static int ax25_release(struct socket *sock)
{
struct sock *sk = sock->sk;
ax25_cb *ax25;
ax25_dev *ax25_dev;
if (sk == NULL)
return 0;
sock_hold(sk);
sock_orphan(sk);
lock_sock(sk);
sock_orphan(sk);
ax25 = sk_to_ax25(sk);
ax25_dev = ax25->ax25_dev;
if (ax25_dev) {
dev_put_track(ax25_dev->dev, &ax25_dev->dev_tracker);
ax25_dev_put(ax25_dev);
}
if (sk->sk_type == SOCK_SEQPACKET) {
switch (ax25->state) {