Re: [PATCH V3] bcachefs: Add journal v2 entry nr value check

From: Kent Overstreet
Date: Tue Aug 20 2024 - 23:00:19 EST


On Wed, Aug 21, 2024 at 10:57:37AM GMT, Lizhi Xu wrote:
> When the nr value of a signle entry or their sum overflows, 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 | 16 +++++++++++++++-
> 1 file changed, 15 insertions(+), 1 deletion(-)
>
> diff --git a/fs/bcachefs/journal_sb.c b/fs/bcachefs/journal_sb.c
> index db80e506e3ab..230ed99130e4 100644
> --- a/fs/bcachefs/journal_sb.c
> +++ b/fs/bcachefs/journal_sb.c
> @@ -107,6 +107,7 @@ static int bch2_sb_journal_v2_validate(struct bch_sb *sb, struct bch_sb_field *f
> unsigned nr;
> unsigned i;
> struct u64_range *b;
> + u64 total_nr = 0, entry_nr;
>
> nr = bch2_sb_field_journal_v2_nr_entries(journal);
> if (!nr)
> @@ -117,8 +118,21 @@ static int bch2_sb_journal_v2_validate(struct bch_sb *sb, struct bch_sb_field *f
> return -BCH_ERR_ENOMEM_sb_journal_v2_validate;
>
> for (i = 0; i < nr; i++) {
> + entry_nr = le64_to_cpu(journal->d[i].nr);
> + if (entry_nr > UINT_MAX) {
> + prt_printf(err, "Journal v2 entry d[%u] nr %llu overflow\n",
> + i, entry_nr);
> + goto err;
> + }

This check is unnecessary; we know the sum can't overflow a u64 because
we're also checking that the entries are nonoverlapping.

> + total_nr += entry_nr;
> b[i].start = le64_to_cpu(journal->d[i].start);
> - b[i].end = b[i].start + le64_to_cpu(journal->d[i].nr);
> + b[i].end = b[i].start + entry_nr;
> + }
> +
> + if (total_nr > UINT_MAX) {
> + prt_printf(err, "Sum of journal v2 entries nr %llu overflow\n",
> + total_nr);
> + goto err;
> }
>
> sort(b, nr, sizeof(*b), u64_range_cmp, NULL);
> --
> 2.43.0
>