Bluetooth: Fix race condition in hci_release_sock()

Syzbot managed to trigger a use after free "KASAN: use-after-free Write
in hci_sock_bind".  I have reviewed the code manually and one possibly
cause I have found is that we are not holding lock_sock(sk) when we do
the hci_dev_put(hdev) in hci_sock_release().  My theory is that the bind
and the release are racing against each other which results in this use
after free.

Reported-by: syzbot+eba992608adf3d796bcc@syzkaller.appspotmail.com
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Johan Hedberg <johan.hedberg@intel.com>

diff --git a/net/bluetooth/hci_sock.c b/net/bluetooth/hci_sock.c
index 5756b124c2cb06f376231dbd8d8add605bd017d7..9c4a093f89607620f7d4c0c633f3bec84f10f751 100644 (file)
--- a/net/bluetooth/hci_sock.c
+++ b/net/bluetooth/hci_sock.c
@@ -839,6 +839,8 @@ static int hci_sock_release(struct socket *sock)
        if (!sk)
                return 0;
 
+       lock_sock(sk);
+
        switch (hci_pi(sk)->channel) {
        case HCI_CHANNEL_MONITOR:
                atomic_dec(&monitor_promisc);
@@ -886,6 +888,7 @@ static int hci_sock_release(struct socket *sock)
        skb_queue_purge(&sk->sk_receive_queue);
        skb_queue_purge(&sk->sk_write_queue);
 
+       release_sock(sk);
        sock_put(sk);
        return 0;
 }