[PATCH] Bluetooth: hci_sock: Prevent race in socket write iter and sock bind

[Edward Adam Davis <eadavis@qq.com>]

There is a potential race condition between sock bind and socket write
iter. bind may free the same cmd via mgmt_pending before write iter sends
the cmd, just as syzbot reported in UAF[1].

Here we use hci_dev_lock to synchronize the two, thereby avoiding the
UAF mentioned in [1].

[1]
syzbot reported:
BUG: KASAN: slab-use-after-free in mgmt_pending_remove+0x3b/0x210 net/bluetooth/mgmt_util.c:316
Read of size 8 at addr ffff888077164818 by task syz.0.17/5989
Call Trace:
 mgmt_pending_remove+0x3b/0x210 net/bluetooth/mgmt_util.c:316
 set_link_security+0x5c2/0x710 net/bluetooth/mgmt.c:1918
 hci_mgmt_cmd+0x9c9/0xef0 net/bluetooth/hci_sock.c:1719
 hci_sock_sendmsg+0x6ca/0xef0 net/bluetooth/hci_sock.c:1839
 sock_sendmsg_nosec net/socket.c:727 [inline]
 __sock_sendmsg+0x21c/0x270 net/socket.c:742
 sock_write_iter+0x279/0x360 net/socket.c:1195

Allocated by task 5989:
 mgmt_pending_add+0x35/0x140 net/bluetooth/mgmt_util.c:296
 set_link_security+0x557/0x710 net/bluetooth/mgmt.c:1910
 hci_mgmt_cmd+0x9c9/0xef0 net/bluetooth/hci_sock.c:1719
 hci_sock_sendmsg+0x6ca/0xef0 net/bluetooth/hci_sock.c:1839
 sock_sendmsg_nosec net/socket.c:727 [inline]
 __sock_sendmsg+0x21c/0x270 net/socket.c:742
 sock_write_iter+0x279/0x360 net/socket.c:1195

Freed by task 5991:
 mgmt_pending_free net/bluetooth/mgmt_util.c:311 [inline]
 mgmt_pending_foreach+0x30d/0x380 net/bluetooth/mgmt_util.c:257
 mgmt_index_removed+0x112/0x2f0 net/bluetooth/mgmt.c:9477
 hci_sock_bind+0xbe9/0x1000 net/bluetooth/hci_sock.c:1314

Fixes: 6fe26f694c82 ("Bluetooth: MGMT: Protect mgmt_pending list with its own lock")
Reported-by: syzbot+9aa47cd4633a3cf92a80@syzkaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=9aa47cd4633a3cf92a80
Tested-by: syzbot+9aa47cd4633a3cf92a80@syzkaller.appspotmail.com
Signed-off-by: Edward Adam Davis <eadavis@qq.com>
---
 net/bluetooth/hci_sock.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/net/bluetooth/hci_sock.c b/net/bluetooth/hci_sock.c
index fc866759910d..ad19022ae127 100644
--- a/net/bluetooth/hci_sock.c
+++ b/net/bluetooth/hci_sock.c
@@ -1311,7 +1311,9 @@ static int hci_sock_bind(struct socket *sock, struct sockaddr *addr,
 			goto done;
 		}
 
+		hci_dev_lock(hdev);
 		mgmt_index_removed(hdev);
+		hci_dev_unlock(hdev);
 
 		err = hci_dev_open(hdev->id);
 		if (err) {
-- 
2.43.0