ext4: validate external journal superblock checksum

If the external journal device has metadata_csum enabled, verify
that the superblock checksum matches the block before we try to
mount.

Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
Reviewed-by: Jan Kara <jack@suse.cz>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>

1 files changed, 9 insertions, 0 deletions

diff --git a/fs/ext4/super.c b/fs/ext4/super.c
index fb219b95f8d2..263201793c65 100644
--- a/fs/ext4/super.c
+++ b/fs/ext4/super.c
@@ -4414,6 +4414,15 @@ static journal_t *ext4_get_dev_journal(struct super_block *sb,
                 goto out_bdev;
         }
 
+        if ((le32_to_cpu(es->s_feature_ro_compat) &
+             EXT4_FEATURE_RO_COMPAT_METADATA_CSUM) &&
+            es->s_checksum != ext4_superblock_csum(sb, es)) {
+                ext4_msg(sb, KERN_ERR, "external journal has "
+                                       "corrupt superblock");
+                brelse(bh);
+                goto out_bdev;
+        }
+
         if (memcmp(EXT4_SB(sb)->s_es->s_journal_uuid, es->s_uuid, 16)) {
                 ext4_msg(sb, KERN_ERR, "journal UUID does not match");
                 brelse(bh);