net: drop write-only stack variable

BugLink: https://bugs.launchpad.net/bugs/1810807

[ Upstream commit 3575dbf2 ]

Remove a write-only stack variable from unix_attach_fds(). This is a
left-over from the security fix in:

    commit 712f4aad
    Author: willy tarreau <w@1wt.eu>
    Date:   Sun Jan 10 07:54:56 2016 +0100

        unix: properly account for FDs passed over unix sockets
Signed-off-by: David Herrmann <dh.herrmann@gmail.com>
Acked-by: Hannes Frederic Sowa <hannes@stressinduktion.org>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Sasha Levin <sashal@kernel.org>
Signed-off-by: Juerg Haefliger <juergh@canonical.com>
Signed-off-by: Kleber Sacilotto de Souza <kleber.souza@canonical.com>

net/unix/af_unix.c

@@ -1531,7 +1531,6 @@ static int unix_attach_fds(struct scm_cookie *scm, struct sk_buff *skb)
 {
 	int i;
 	unsigned char max_level = 0;
-	int unix_sock_count = 0;
 
 	if (too_many_unix_fds(current))
 		return -ETOOMANYREFS;
@@ -1539,11 +1538,9 @@ static int unix_attach_fds(struct scm_cookie *scm, struct sk_buff *skb)
 	for (i = scm->fp->count - 1; i >= 0; i--) {
 		struct sock *sk = unix_get_socket(scm->fp->fp[i]);
 
-		if (sk) {
-			unix_sock_count++;
+		if (sk)
 			max_level = max(max_level,
 					unix_sk(sk)->recursion_level);
-		}
 	}
 	if (unlikely(max_level > MAX_RECURSION_LEVEL))
 		return -ETOOMANYREFS;