Do not send SMB3 SET_INFO request if nothing is changing

BugLink: http://bugs.launchpad.net/bugs/1637510

commit 18dd8e1a upstream.

[CIFS] We had cases where we sent a SMB2/SMB3 setinfo request with all
timestamp (and DOS attribute) fields marked as 0 (ie do not change)
e.g. on chmod or chown.
Signed-off-by: Steve French <steve.french@primarydata.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Tim Gardner <tim.gardner@canonical.com>

fs/cifs/smb2inode.c

@@ -266,9 +266,15 @@ smb2_set_file_info(struct inode *inode, const char *full_path,
 	struct tcon_link *tlink;
 	int rc;
 
+	if ((buf->CreationTime == 0) && (buf->LastAccessTime == 0) &&
+	    (buf->LastWriteTime == 0) && (buf->ChangeTime) &&
+	    (buf->Attributes == 0))
+		return 0; /* would be a no op, no sense sending this */
+
 	tlink = cifs_sb_tlink(cifs_sb);
 	if (IS_ERR(tlink))
 		return PTR_ERR(tlink);
+
 	rc = smb2_open_op_close(xid, tlink_tcon(tlink), cifs_sb, full_path,
 				FILE_WRITE_ATTRIBUTES, FILE_OPEN, 0, buf,
 				SMB2_OP_SET_INFO);