Re: [PATCH 3/4] mm: swap: fix potensial buffer overflow in setup_clusters()

[Kairui Song]

On Thu, May 22, 2025 at 11:32 AM Kemeng Shi <shikemeng@xxxxxxxxxxxxxxx> wrote:
>
> In setup_swap_map(), we only ensure badpages are in range (0, last_page].
> As maxpages might be < last_page, setup_clusters() will encounter a
> buffer overflow when a badpage is >= maxpages.
> Only call inc_cluster_info_page() for badpage which is < maxpages to
> fix the issue.
>
> Fixes: b843786b0bd01 ("mm: swapfile: fix SSD detection with swapfile on btrfs")
> Signed-off-by: Kemeng Shi <shikemeng@xxxxxxxxxxxxxxx>
> ---
>  mm/swapfile.c | 10 +++++++---
>  1 file changed, 7 insertions(+), 3 deletions(-)
>
> diff --git a/mm/swapfile.c b/mm/swapfile.c
> index a82f4ebefca3..63ab9f14b2c6 100644
> --- a/mm/swapfile.c
> +++ b/mm/swapfile.c
> @@ -3208,9 +3208,13 @@ static struct swap_cluster_info *setup_clusters(struct swap_info_struct *si,
>          * and the EOF part of the last cluster.
>          */
>         inc_cluster_info_page(si, cluster_info, 0);
> -       for (i = 0; i < swap_header->info.nr_badpages; i++)
> -               inc_cluster_info_page(si, cluster_info,
> -                                     swap_header->info.badpages[i]);
> +       for (i = 0; i < swap_header->info.nr_badpages; i++) {
> +               unsigned int page_nr = swap_header->info.badpages[i];
> +
> +               if (page_nr >= maxpages)
> +                       continue;
> +               inc_cluster_info_page(si, cluster_info, page_nr);

I think we might need a pr_err or pr_warn here, this means mkswap
marked the wrong region as a bad block? Or some fs side things went
wrong.


> +       }
>         for (i = maxpages; i < round_up(maxpages, SWAPFILE_CLUSTER); i++)
>                 inc_cluster_info_page(si, cluster_info, i);
>
> --
> 2.30.0
>
>