jbd2: fix the inconsistency between checksum and data in memory for journal sb

Copying the file system while it is mounted as read-only results in
a mount failure:
[~]# mkfs.ext4 -F /dev/sdc
[~]# mount /dev/sdc -o ro /mnt/test
[~]# dd if=/dev/sdc of=/dev/sda bs=1M
[~]# mount /dev/sda /mnt/test1
[ 1094.849826] JBD2: journal checksum error
[ 1094.850927] EXT4-fs (sda): Could not load journal inode
mount: mount /dev/sda on /mnt/test1 failed: Bad message

The process described above is just an abstracted way I came up with to
reproduce the issue. In the actual scenario, the file system was mounted
read-only and then copied while it was still mounted. It was found that
the mount operation failed. The user intended to verify the data or use
it as a backup, and this action was performed during a version upgrade.
Above issue may happen as follows:
ext4_fill_super
 set_journal_csum_feature_set(sb)
  if (ext4_has_metadata_csum(sb))
   incompat = JBD2_FEATURE_INCOMPAT_CSUM_V3;
  if (test_opt(sb, JOURNAL_CHECKSUM)
   jbd2_journal_set_features(sbi->s_journal, compat, 0, incompat);
    lock_buffer(journal->j_sb_buffer);
    sb->s_feature_incompat  |= cpu_to_be32(incompat);
    //The data in the journal sb was modified, but the checksum was not
      updated, so the data remaining in memory has a mismatch between the
      data and the checksum.
    unlock_buffer(journal->j_sb_buffer);

In this case, the journal sb copied over is in a state where the checksum
and data are inconsistent, so mounting fails.
To solve the above issue, update the checksum in memory after modifying
the journal sb.

Fixes: 4fd5ea43bc11 ("jbd2: checksum journal superblock")
Signed-off-by: Ye Bin <yebin10@huawei.com>
Reviewed-by: Baokun Li <libaokun1@huawei.com>
Reviewed-by: Darrick J. Wong <djwong@kernel.org>
Reviewed-by: Jan Kara <jack@suse.cz>
Message-ID: <20251103010123.3753631-1-yebin@huaweicloud.com>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
Cc: stable@kernel.org

diff --git a/fs/jbd2/journal.c b/fs/jbd2/journal.c
index 2fe1786a8f1b8db798ed7276a316d52944887d9f..c973162d5b31644921e6ec5fdc96fafce390a0ba 100644 (file)
--- a/fs/jbd2/journal.c
+++ b/fs/jbd2/journal.c
@@ -2354,6 +2354,12 @@ int jbd2_journal_set_features(journal_t *journal, unsigned long compat,
        sb->s_feature_compat    |= cpu_to_be32(compat);
        sb->s_feature_ro_compat |= cpu_to_be32(ro);
        sb->s_feature_incompat  |= cpu_to_be32(incompat);
+       /*
+        * Update the checksum now so that it is valid even for read-only
+        * filesystems where jbd2_write_superblock() doesn't get called.
+        */
+       if (jbd2_journal_has_csum_v2or3(journal))
+               sb->s_checksum = jbd2_superblock_csum(sb);
        unlock_buffer(journal->j_sb_buffer);
        jbd2_journal_init_transaction_limits(journal);
 
@@ -2383,9 +2389,17 @@ void jbd2_journal_clear_features(journal_t *journal, unsigned long compat,
 
        sb = journal->j_superblock;
 
+       lock_buffer(journal->j_sb_buffer);
        sb->s_feature_compat    &= ~cpu_to_be32(compat);
        sb->s_feature_ro_compat &= ~cpu_to_be32(ro);
        sb->s_feature_incompat  &= ~cpu_to_be32(incompat);
+       /*
+        * Update the checksum now so that it is valid even for read-only
+        * filesystems where jbd2_write_superblock() doesn't get called.
+        */
+       if (jbd2_journal_has_csum_v2or3(journal))
+               sb->s_checksum = jbd2_superblock_csum(sb);
+       unlock_buffer(journal->j_sb_buffer);
        jbd2_journal_init_transaction_limits(journal);
 }
 EXPORT_SYMBOL(jbd2_journal_clear_features);