xfs: reject completely bogus remount options

There's a long comment about handling non-remountable options in xfs_fs_remount, but nothing addresses the case of completely bogus mount options at remount time, which can lead to some severe strangeness:

# for I in `seq 1 10`; do mount -o remount,noacl /mnt/test2; done
# for I in `seq 1 10`; do mount -o remount,badoption /mnt/test2; done
# grep sdb4 /etc/mtab
/dev/sdb4 /mnt/test2 xfs rw,noacl,noacl,noacl,noacl,noacl,noacl,noacl,noacl,noacl,noacl,noacl,badoption,badoption,badoption,badoption,badoption,badoption,badoption,badoption,badoption,badoption 0 0

This is a bit of a hack, but we can re-use xfs_parseargs() with a dummy mount struct to just vet all of the remount options which were passed in. With this, we get a saner result:

[44898.102990] EXT4-fs (sdb4): Unrecognized mount option "badoption" or missing value

if we try to remount with something ridiculous.

In the long run we should probably revamp a lot of the mount option handling...

---

index 9a72dda..0402f9c 100644
@@ -1157,11 +1157,22 @@ xfs_fs_remount(
 	int			*flags,
 	char			*options)
 {
-	struct xfs_mount	*mp = XFS_M(sb);
+	struct xfs_mount	*mp = XFS_M(sb), dummy_mp;
 	substring_t		args[MAX_OPT_ARGS];
 	char			*p;
 	int			error;
 
+	/*
+	 * Check all the mount options presented to be sure
+	 * there's nothing too crazy in there.  Non-remountable
+	 * but valid options are a different issue.
+	 */
+	memset(&dummy_mp, 0, sizeof(struct xfs_mount));
+	dummy_mp.m_super = sb;
+	error = xfs_parseargs(&dummy_mp, options);
+	if (error)
+		return -error;
+
 	while ((p = strsep(&options, ",")) != NULL) {
 		int token;
 

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