[PATCH 5.5 22/23] Bluetooth: Fix race condition in hci_release_sock()

Greg Kroah-Hartman
2020-02-03T16:38:31Z

From: Dan Carpenter <dan.carpenter@oracle.com>

commit 11eb85ec42dc8c7a7ec519b90ccf2eeae9409de8 upstream.

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>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
net/bluetooth/hci_sock.c | 3 +++
1 file changed, 3 insertions(+)

--- a/net/bluetooth/hci_sock.c
+++ b/net/bluetooth/hci_sock.c
@@ -831,6 +831,8 @@ static int hci_sock_release(struct socke
if (!sk)
return 0;

+ lock_sock(sk);
+
switch (hci_pi(sk)->channel) {
case HCI_CHANNEL_MONITOR:
atomic_dec(&monitor_promisc);
@@ -878,6 +880,7 @@ static int hci_sock_release(struct socke
skb_queue_purge(&sk->sk_receive_queue);
skb_queue_purge(&sk->sk_write_queue);

+ release_sock(sk);
sock_put(sk);
return 0;
}