cifs: modefromsid: make room for 4 ACE

when mounting with modefromsid, we end up writing 4 ACE in a security
descriptor that only has room for 3, thus triggering an out-of-bounds
write. fix this by changing the min size of a security descriptor.
Signed-off-by: Aurelien Aptel <aaptel@suse.com>
Signed-off-by: Steve French <stfrench@microsoft.com>

fs/cifs/cifsacl.h

@@ -45,7 +45,7 @@
  */
 #define DEFAULT_SEC_DESC_LEN (sizeof(struct cifs_ntsd) + \
 			      sizeof(struct cifs_acl) + \
-			      (sizeof(struct cifs_ace) * 3))
+			      (sizeof(struct cifs_ace) * 4))
 
 /*
  * Maximum size of a string representation of a SID: