Re: [syzbot] KASAN: use-after-free Write in sco_sock_timeout

On 30/8/21 8:15 am, Hillf Danton wrote:

On Mon, 30 Aug 2021 02:34:11 +0800 Desmond Cheong Zhi Xi wrote:

quoted

Ok I went back to make a more thorough audit. Even without calling
cancel_delayed_work_sync, sco_sock_timeout should not cause a UAF.

I believe the real issue is that we can allocate a connection twice in
sco_connect. This means that the first connection gets lost and we're
unable to clean it up properly.

Thoughts on this?

LGTM regardless of the uaf reported.

Hillf

Thanks for taking a look. It passed the Syzbot reproducer too, so I 
think the root cause should have been addressed.

I'll write up a patch to summarize what we found out. May I include you 
as a Co-developed-by: author?

quoted

#syz test: git://git.kernel.org/pub/scm/linux/kernel/git/netdev/net-next.git e3f30ab28ac8

--- a/net/bluetooth/sco.c
+++ b/net/bluetooth/sco.c

@@ -578,9 +578,6 @@ static int sco_sock_connect(struct socket *sock, struct sockaddr *addr, int alen
  	    addr->sa_family != AF_BLUETOOTH)
  		return -EINVAL;
  
-	if (sk->sk_state != BT_OPEN && sk->sk_state != BT_BOUND)
-		return -EBADFD;
-
  	if (sk->sk_type != SOCK_SEQPACKET)
  		return -EINVAL;
  

@@ -591,6 +588,13 @@ static int sco_sock_connect(struct socket *sock, struct sockaddr *addr, int alen
  
  	lock_sock(sk);
  
+	if (sk->sk_state != BT_OPEN && sk->sk_state != BT_BOUND) {
+		hci_dev_unlock(hdev);
+		hci_dev_put(hdev);
+		err = -EBADFD;
+		goto done;
+	}
+
  	/* Set destination address and psm */
  	bacpy(&sco_pi(sk)->dst, &sa->sco_bdaddr);