smb: client: allow parsing zero-length AV pairs

Zero-length AV pairs should be considered as valid target infos.
Don't skip the next AV pairs that follow them.

Cc: linux-cifs@vger.kernel.org
Cc: David Howells <dhowells@redhat.com>
Fixes: 0e8ae9b ("smb: client: parse av pair type 4 in CHALLENGE_MESSAGE")
Signed-off-by: Paulo Alcantara (Red Hat) <pc@manguebit.org>
Signed-off-by: Steve French <stfrench@microsoft.com>

Author: pcacjr

fs/smb/client/cifsencrypt.c

@@ -343,7 +343,7 @@ static struct ntlmssp2_name *find_next_av(struct cifs_ses *ses,
 	len = AV_LEN(av);
 	if (AV_TYPE(av) == NTLMSSP_AV_EOL)
 		return NULL;
-	if (!len || (u8 *)av + sizeof(*av) + len > end)
+	if ((u8 *)av + sizeof(*av) + len > end)
 		return NULL;
 	return av;
 }
@@ -363,7 +363,7 @@ static int find_av_name(struct cifs_ses *ses, u16 type, char **name, u16 maxlen)
 
 	av_for_each_entry(ses, av) {
 		len = AV_LEN(av);
-		if (AV_TYPE(av) != type)
+		if (AV_TYPE(av) != type || !len)
 			continue;
 		if (!IS_ALIGNED(len, sizeof(__le16))) {
 			cifs_dbg(VFS | ONCE, "%s: bad length(%u) for type %u\n",