cifs: check MaxPathNameComponentLength != 0 before using it

BugLink: http://bugs.launchpad.net/bugs/1731915

commit f74bc7c6 upstream.

And fix tcon leak in error path.
Signed-off-by: Ronnie Sahlberg <lsahlber@redhat.com>
Signed-off-by: Steve French <smfrench@gmail.com>
Reviewed-by: David Disseldorp <ddiss@samba.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Stefan Bader <stefan.bader@canonical.com>
Signed-off-by: Thadeu Lima de Souza Cascardo <cascardo@canonical.com>

fs/cifs/dir.c

@@ -193,7 +193,8 @@ check_name(struct dentry *direntry, struct cifs_tcon *tcon)
 	struct cifs_sb_info *cifs_sb = CIFS_SB(direntry->d_sb);
 	int i;
 
-	if (unlikely(direntry->d_name.len >
+	if (unlikely(tcon->fsAttrInfo.MaxPathNameComponentLength &&
+		     direntry->d_name.len >
 		     le32_to_cpu(tcon->fsAttrInfo.MaxPathNameComponentLength)))
 		return -ENAMETOOLONG;
 
@@ -509,7 +510,7 @@ cifs_atomic_open(struct inode *inode, struct dentry *direntry,
 
 	rc = check_name(direntry, tcon);
 	if (rc)
-		goto out_free_xid;
+		goto out;
 
 	server = tcon->ses->server;