[SRU][Focal/Jammy][PATCH] Bluetooth: af_bluetooth: Fix Use-After-Free in bt_sock_recvmsg

[Yuxuan Luo]

From: Hyunwoo Kim <v4bel at theori.io>

This can cause a race with bt_sock_ioctl() because
bt_sock_recvmsg() gets the skb from sk->sk_receive_queue
and then frees it without holding lock_sock.
A use-after-free for a skb occurs with the following flow.
```
bt_sock_recvmsg() -> skb_recv_datagram() -> skb_free_datagram()
bt_sock_ioctl() -> skb_peek()
```
Add lock_sock to bt_sock_recvmsg() to fix this issue.

Cc: stable at vger.kernel.org
Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
Signed-off-by: Hyunwoo Kim <v4bel at theori.io>
Signed-off-by: Luiz Augusto von Dentz <luiz.von.dentz at intel.com>
(backported from commit 2e07e8348ea454615e268222ae3fc240421be768)
[yuxuan.luo: The prerequisite commit, f4b41f062c42 (“net: remove noblock
 parameter from skb_recv_datagram()”), only removes the obsolete
 parameter, ignore this commit and backport the fix manually.
]
CVE-2023-51779
Signed-off-by: Yuxuan Luo <yuxuan.luo at canonical.com>
---
 net/bluetooth/af_bluetooth.c | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/net/bluetooth/af_bluetooth.c b/net/bluetooth/af_bluetooth.c
index ce744b14d1a98..b7498e890f0b0 100644
--- a/net/bluetooth/af_bluetooth.c
+++ b/net/bluetooth/af_bluetooth.c
@@ -263,11 +263,14 @@ int bt_sock_recvmsg(struct socket *sock, struct msghdr *msg, size_t len,
 	if (flags & MSG_OOB)
 		return -EOPNOTSUPP;
 
+	lock_sock(sk);
+
 	skb = skb_recv_datagram(sk, flags, noblock, &err);
 	if (!skb) {
 		if (sk->sk_shutdown & RCV_SHUTDOWN)
-			return 0;
+			err = 0;
 
+		release_sock(sk);
 		return err;
 	}
 
@@ -293,6 +296,8 @@ int bt_sock_recvmsg(struct socket *sock, struct msghdr *msg, size_t len,
 
 	skb_free_datagram(sk, skb);
 
+	release_sock(sk);
+
 	if (flags & MSG_TRUNC)
 		copied = skblen;
 
-- 
2.34.1