ext4: don't try to processed freed blocks until mballoc is initialized

If we try to make any changes via the journal between when the journal
is initialized, but before the multi-block allocated is initialized,
we will end up deferencing a NULL pointer when the journal commit
callback function calls ext4_process_freed_data().

The proximate cause of this failure was commit 2d01ddc86606 ("ext4:
save error info to sb through journal if available") since file system
corruption problems detected before the call to ext4_mb_init() would
result in a journal commit before we aborted the mount of the file
system.... and we would then trigger the NULL pointer deref.

Link: https://lore.kernel.org/r/YAm8qH/0oo2ofSMR@mit.edu
Reported-by: Murphy Zhou <jencce.kernel@gmail.com>
Reviewed-by: Jan Kara <jack@suse.cz>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>

diff --git a/fs/ext4/super.c b/fs/ext4/super.c
index f361f9f..071d131 100644 (file)
--- a/fs/ext4/super.c
+++ b/fs/ext4/super.c
@@ -4875,7 +4875,6 @@ static int ext4_fill_super(struct super_block *sb, void *data, int silent)
 
        set_task_ioprio(sbi->s_journal->j_task, journal_ioprio);
 
-       sbi->s_journal->j_commit_callback = ext4_journal_commit_callback;
        sbi->s_journal->j_submit_inode_data_buffers =
                ext4_journal_submit_inode_data_buffers;
        sbi->s_journal->j_finish_inode_data_buffers =
@@ -4987,6 +4986,14 @@ no_journal:
                goto failed_mount5;
        }
 
+       /*
+        * We can only set up the journal commit callback once
+        * mballoc is initialized
+        */
+       if (sbi->s_journal)
+               sbi->s_journal->j_commit_callback =
+                       ext4_journal_commit_callback;
+
        block = ext4_count_free_clusters(sb);
        ext4_free_blocks_count_set(sbi->s_es, 
                                   EXT4_C2B(sbi, block));