ext4: update s_journal_inum if it changes after journal replay

When mounting a crafted ext4 image, s_journal_inum may change after journal
replay, which is obviously unreasonable because we have successfully loaded
and replayed the journal through the old s_journal_inum. And the new
s_journal_inum bypasses some of the checks in ext4_get_journal(), which
may trigger a null pointer dereference problem. So if s_journal_inum
changes after the journal replay, we ignore the change, and rewrite the
current journal_inum to the superblock.

Link: https://bugzilla.kernel.org/show_bug.cgi?id=216541
Reported-by: Luís Henriques <lhenriques@suse.de>
Signed-off-by: Baokun Li <libaokun1@huawei.com>
Reviewed-by: Jan Kara <jack@suse.cz>
Link: https://lore.kernel.org/r/20230107032126.4165860-3-libaokun1@huawei.com
Signed-off-by: Theodore Ts'o <tytso@mit.edu>

diff --git a/fs/ext4/super.c b/fs/ext4/super.c
index 3b9e30e..45bcfd3 100644 (file)
--- a/fs/ext4/super.c
+++ b/fs/ext4/super.c
@@ -5953,8 +5953,11 @@ static int ext4_load_journal(struct super_block *sb,
        if (!really_read_only && journal_devnum &&
            journal_devnum != le32_to_cpu(es->s_journal_dev)) {
                es->s_journal_dev = cpu_to_le32(journal_devnum);
-
-               /* Make sure we flush the recovery flag to disk. */
+               ext4_commit_super(sb);
+       }
+       if (!really_read_only && journal_inum &&
+           journal_inum != le32_to_cpu(es->s_journal_inum)) {
+               es->s_journal_inum = cpu_to_le32(journal_inum);
                ext4_commit_super(sb);
        }