Re: [PATCH V2] bcachefs: Add journal v2 entry nr value check

[Kent Overstreet]

On Tue, Aug 20, 2024 at 03:11:45PM GMT, Lizhi Xu wrote:
> When journal v2 entry nr overflow, it will cause the value of ja->nr to
> be incorrect, this will result in the allocated memory to ja->buckets
> being too small, leading to out of bounds access in bch2_dev_journal_init.
> 
> Reported-by: syzbot+47ecc948aadfb2ab3efc@xxxxxxxxxxxxxxxxxxxxxxxxx
> Signed-off-by: Lizhi Xu <lizhi.xu@xxxxxxxxxxxxx>
> ---
>  fs/bcachefs/journal_sb.c | 5 +++++
>  1 file changed, 5 insertions(+)
> 
> diff --git a/fs/bcachefs/journal_sb.c b/fs/bcachefs/journal_sb.c
> index db80e506e3ab..db2b2100e4e5 100644
> --- a/fs/bcachefs/journal_sb.c
> +++ b/fs/bcachefs/journal_sb.c
> @@ -119,6 +119,11 @@ static int bch2_sb_journal_v2_validate(struct bch_sb *sb, struct bch_sb_field *f
>  	for (i = 0; i < nr; i++) {
>  		b[i].start = le64_to_cpu(journal->d[i].start);
>  		b[i].end = b[i].start + le64_to_cpu(journal->d[i].nr);
> +		if (le64_to_cpu(journal->d[i].nr) > UINT_MAX) {
> +			prt_printf(err, "journal v2 entry d[%u].nr %llu overflow\n",
> +				i, le64_to_cpu(journal->d[i].nr));
> +			goto err;
> +		}

no, you need to sum up _all_ the entries and verify the total doesn't
overflow UINT_MAX