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[PATCH 2/4] xfs: reject completely bogus remount options

To: Eric Sandeen <sandeen@xxxxxxxxxx>
Subject: [PATCH 2/4] xfs: reject completely bogus remount options
From: Eric Sandeen <sandeen@xxxxxxxxxxx>
Date: Fri, 11 Oct 2013 14:11:18 -0500
Cc: xfs-oss <xfs@xxxxxxxxxxx>
Delivered-to: xfs@xxxxxxxxxxx
In-reply-to: <52584C8A.1060808@xxxxxxxxxx>
References: <52584C8A.1060808@xxxxxxxxxx>
User-agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.8; rv:17.0) Gecko/20130801 Thunderbird/17.0.8
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>
---

Note, not really sure what KM_* flag would be appropriate here,
if it fails, it really is ok, other than missing the verification.
But maybe that's too "nice?"

commit 72e6ddd901dc8a8ecb835324eb4e11b0d7ad8cf8
Author: Eric Sandeen <sandeen@xxxxxxxxxx>
Date:   Fri Oct 11 14:03:59 2013 -0500

    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...
    
    Signed-off-by: Eric Sandeen <sandeen@xxxxxxxxxx>

diff --git a/fs/xfs/xfs_super.c b/fs/xfs/xfs_super.c
index 15188cc..00a06d6 100644
--- a/fs/xfs/xfs_super.c
+++ b/fs/xfs/xfs_super.c
@@ -1202,11 +1202,25 @@ 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.
+        */
+       dummy_mp = kmem_zalloc(sizeof(*dummy_mp), KM_MAYFAIL);
+       if (dummy_mp) {
+               dummy_mp->m_super = sb;
+               error = xfs_parseargs(dummy_mp, options);
+               kfree(dummy_mp);
+               if (error)
+                       return -error;
+       }
+
        while ((p = strsep(&options, ",")) != NULL) {
                int token;
 

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