[PATCH] xfs: reject completely bogus remount options

[Eric Sandeen]

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...

Signed-off-by: Eric Sandeen <sandeen at redhat.com>
---

diff --git a/fs/xfs/linux-2.6/xfs_super.c b/fs/xfs/linux-2.6/xfs_super.c
index 9a72dda..0402f9c 100644
--- a/fs/xfs/linux-2.6/xfs_super.c
+++ b/fs/xfs/linux-2.6/xfs_super.c
@@ -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;