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[PATCH] xfs: reject completely bogus remount options

To: xfs-oss <xfs@xxxxxxxxxxx>
Subject: [PATCH] xfs: reject completely bogus remount options
From: Eric Sandeen <sandeen@xxxxxxxxxx>
Date: Tue, 05 Jun 2012 11:41:36 -0500
Cc: Vijay Bellur <vbellur@xxxxxxxxxx>
User-agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.6; rv:12.0) Gecko/20120428 Thunderbird/12.0.1
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@xxxxxxxxxx>
---

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;
 

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