@@ -77,6 +77,7 @@ static void ax25_kill_by_device(struct net_device *dev)
{
ax25_dev *ax25_dev;
ax25_cb *s;
+ struct sock *sk;
if ((ax25_dev = ax25_dev_ax25dev(dev)) == NULL)
return;
@@ -85,13 +86,15 @@ static void ax25_kill_by_device(struct net_device *dev)
again:
ax25_for_each(s, &ax25_list) {
if (s->ax25_dev == ax25_dev) {
+ sk = s->sk;
+ sock_hold(sk);
spin_unlock_bh(&ax25_list_lock);
- lock_sock(s->sk);
+ lock_sock(sk);
s->ax25_dev = NULL;
- release_sock(s->sk);
+ release_sock(sk);
ax25_disconnect(s, ENETUNREACH);
spin_lock_bh(&ax25_list_lock);
-
+ sock_put(sk);
/* The entry could have been deleted from the
* list meanwhile and thus the next pointer is
* no longer valid. Play it safe and restart
The previous commit 1ade48d0c27d ("ax25: NPD bug when detaching AX25 device") introduce lock_sock() into ax25_kill_by_device to prevent NPD bug. But the concurrency NPD or UAF bug will occur, when lock_sock() or release_sock() dereferences the ax25_cb->sock. The NULL pointer dereference bug can be shown as below: ax25_kill_by_device() | ax25_release() | ax25_destroy_socket() | ax25_cb_del() ... | ... | ax25->sk=NULL; lock_sock(s->sk); //(1) | s->ax25_dev = NULL; | ... release_sock(s->sk); //(2) | ... | The root cause is that the sock is set to null before dereference site (1) or (2). Therefore, this patch extracts the ax25_cb->sock in advance, and uses ax25_list_lock to protect it, which can synchronize with ax25_cb_del() and ensure the value of sock is not null before dereference sites. The concurrency UAF bug can be shown as below: ax25_kill_by_device() | ax25_release() | ax25_destroy_socket() ... | ... | sock_put(sk); //FREE lock_sock(s->sk); //(1) | s->ax25_dev = NULL; | ... release_sock(s->sk); //(2) | ... | The root cause is that the sock is released before dereference site (1) or (2). Therefore, this patch uses sock_hold() to increase the refcount of sock and uses ax25_list_lock to protect it, which can synchronize with ax25_cb_del() in ax25_destroy_socket() and ensure the sock wil not be released before dereference sites. Signed-off-by: Duoming Zhou <duoming@zju.edu.cn> --- net/ax25/af_ax25.c | 9 ++++++--- 1 file changed, 6 insertions(+), 3 deletions(-)