From: Theodore Ts'o <tytso@mit.edu>

[ Upstream commit 027f14f5357279655c3ebc6d14daff8368d4f53f ]

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 <redacted>
Reviewed-by: Jan Kara <jack@suse.cz>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 fs/ext4/super.c | 9 ++++++++-
 1 file changed, 8 insertions(+), 1 deletion(-)

diff --git a/fs/ext4/super.c b/fs/ext4/super.c
index 9a6f9875aa34..2ae0af1c88c7 100644
--- 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));

-- 
2.30.1