From 11eb85ec42dc8c7a7ec519b90ccf2eeae9409de8 Mon Sep 17 00:00:00 2001
From: Dan Carpenter <dan.carpenter@oracle.com>
Date: Wed, 15 Jan 2020 20:49:04 +0300
Subject: [PATCH] Bluetooth: Fix race condition in hci_release_sock()
Git-commit: 11eb85ec42dc8c7a7ec519b90ccf2eeae9409de8
Patch-mainline: v5.6-rc1
References: bsc#1051510

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>
Acked-by: Takashi Iwai <tiwai@suse.de>

---
 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 5756b124c2cb..9c4a093f8960 100644
--- 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;
 }
-- 
2.16.4