Re: [PATCH] bcachefs: Add checks for entry's _data bytes

[Kent Overstreet]

On Tue, Jul 30, 2024 at 12:10:19PM GMT, Edward Adam Davis wrote:
> syzbot report slab-out-of-bounds in journal_entry_dev_usage_to_text,
> it because vstruct_bytes(entry) smaller than sizeof(struct 
> jset_entry_dev_usage), overflow occurs when calculating the difference in
> jset_entry_dev_usage_nr_types(u).
> 
> Reported-by: syzbot+05d7520be047c9be86e0@xxxxxxxxxxxxxxxxxxxxxxxxx
> Closes: https://syzkaller.appspot.com/bug?extid=05d7520be047c9be86e0
> Signed-off-by: Edward Adam Davis <eadavis@xxxxxx>
> ---
>  fs/bcachefs/sb-clean.c | 3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/fs/bcachefs/sb-clean.c b/fs/bcachefs/sb-clean.c
> index 47f10ab57f40..278e1a25159a 100644
> --- a/fs/bcachefs/sb-clean.c
> +++ b/fs/bcachefs/sb-clean.c
> @@ -310,6 +310,9 @@ static void bch2_sb_clean_to_text(struct printbuf *out, struct bch_sb *sb,
>  		    !entry->u64s)
>  			continue;
>  
> +		if (vstruct_bytes(entry) < sizeof(struct jset_entry_dev_usage))
> +			continue;

This is wrong: you haven't checked the entry type and you're assuming
it's a dev_usage entry.

The check should go in journal_entry_dev_usage_to_text().