From: Duoming Zhou duoming@zju.edu.cn
[ Upstream commit 4e0f718daf97d47cf7dec122da1be970f145c809 ]
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 Signed-off-by: David S. Miller davem@davemloft.net Signed-off-by: Sasha Levin sashal@kernel.org --- net/ax25/af_ax25.c | 9 ++++++--- 1 file changed, 6 insertions(+), 3 deletions(-)
diff --git a/net/ax25/af_ax25.c b/net/ax25/af_ax25.c index 0232afd9d9c3c..36d2e1dfa1e6b 100644 --- a/net/ax25/af_ax25.c +++ b/net/ax25/af_ax25.c @@ -80,6 +80,7 @@ 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; @@ -88,13 +89,15 @@ 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- + sock_put(sk); /* The entry could have been deleted from the * list meanwhile and thus the next pointer is * no longer valid.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