CIFS: ignore mode change if it's just for clearing setuid/setgid bits

If the ATTR_KILL_S*ID bits are set then any mode change is only for clearing
the setuid/setgid bits.  For CIFS, skip the mode change and let the server
handle it.
Signed-off-by: Jeff Layton <jlayton@redhat.com>
Cc: Steven French <sfrench@us.ibm.com>
Cc: Christoph Hellwig <hch@lst.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

fs/cifs/inode.c

@@ -1538,6 +1538,11 @@ int cifs_setattr(struct dentry *direntry, struct iattr *attrs)
 	}
 
 	time_buf.Attributes = 0;
+
+	/* skip mode change if it's just for clearing setuid/setgid */
+	if (attrs->ia_valid & (ATTR_KILL_SUID|ATTR_KILL_SGID))
+		attrs->ia_valid &= ~ATTR_MODE;
+
 	if (attrs->ia_valid & ATTR_MODE) {
 		cFYI(1, ("Mode changed to 0x%x", attrs->ia_mode));
 		mode = attrs->ia_mode;