ext4: disallow changing journal_csum option during remount

ext4 does not permit changing the metadata or journal checksum feature
flag while mounted.  Until we decide to support that, don't allow a
remount to change the journal_csum flag (right now we silently fail to
change anything).

Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>

1 files changed, 8 insertions, 0 deletions

diff --git a/fs/ext4/super.c b/fs/ext4/super.c
index 5c11e2153e36..96059e0ef165 100644
--- a/fs/ext4/super.c
+++ b/fs/ext4/super.c
@@ -4845,6 +4845,14 @@ static int ext4_remount(struct super_block *sb, int *flags, char *data)
                 goto restore_opts;
         }
 
+        if ((old_opts.s_mount_opt & EXT4_MOUNT_JOURNAL_CHECKSUM) ^
+            test_opt(sb, JOURNAL_CHECKSUM)) {
+                ext4_msg(sb, KERN_ERR, "changing journal_checksum "
+                         "during remount not supported");
+                err = -EINVAL;
+                goto restore_opts;
+        }
+
         if (test_opt(sb, DATA_FLAGS) == EXT4_MOUNT_JOURNAL_DATA) {
                 if (test_opt2(sb, EXPLICIT_DELALLOC)) {
                         ext4_msg(sb, KERN_ERR, "can't mount with "