[PATCH] xfs: disallow ro->rw remount on norecovery mount

[Eric Sandeen <sandeen@xxxxxxxxxx>]

There's a bit of a loophole in norecovery mount handling right
now: an initial mount must be readonly, but nothing prevents
a mount -o remount,rw from producing a writable, unrecovered
xfs filesystem.

It might be possible to try to perform a log recovery when this
is requested, but I'm not sure it's worth the effort.  For now,
simply disallow this sort of transition.

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

diff --git a/fs/xfs/xfs_super.c b/fs/xfs/xfs_super.c
index 8fcc4cc..a6cc7a9 100644
--- a/fs/xfs/xfs_super.c
+++ b/fs/xfs/xfs_super.c
@@ -1256,6 +1256,12 @@ xfs_fs_remount(
 
        /* ro -> rw */
        if ((mp->m_flags & XFS_MOUNT_RDONLY) && !(*flags & MS_RDONLY)) {
+               if (mp->m_flags & XFS_MOUNT_NORECOVERY) {
+                       xfs_warn(mp,
+               "ro->rw transition prohibited on norecovery mount");
+                       return -EINVAL;
+               }
+
                mp->m_flags &= ~XFS_MOUNT_RDONLY;
 
                /*