netdev - [PATCH] Bluetooth: Fix race condition in hci_release

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Date:   Wed, 15 Jan 2020 20:49:04 +0300
From:   Dan Carpenter <dan.carpenter@...cle.com>
To:     Marcel Holtmann <marcel@...tmann.org>,
        syzbot <syzbot+eba992608adf3d796bcc@...kaller.appspotmail.com>
Cc:     Johan Hedberg <johan.hedberg@...il.com>,
        "David S. Miller" <davem@...emloft.net>,
        linux-bluetooth@...r.kernel.org, netdev@...r.kernel.org,
        marcel@...tmann.org, syzkaller-bugs@...glegroups.com
Subject: [PATCH] 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@...kaller.appspotmail.com
Signed-off-by: Dan Carpenter <dan.carpenter@...cle.com>
---
Not tested!  Please review very very carefully!

I feel like maybe someone should audit the (struct proto_ops)->release()
functions because there may be similar bugs to this in other drivers.

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

diff --git a/net/bluetooth/hci_sock.c b/net/bluetooth/hci_sock.c
index 5d0ed28c0d3a..c86598ff4283 100644
--- a/net/bluetooth/hci_sock.c
+++ b/net/bluetooth/hci_sock.c
@@ -831,6 +831,8 @@ 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);
@@ -878,6 +880,7 @@ 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;
 }
-- 
2.11.0