linux-kernel - Re: [PATCH 2/9] mm/z3fold: fix possible null pointer dereferencing

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Date:   Thu, 19 May 2022 09:04:30 +0200
From:   Vitaly Wool <vitaly.wool@...sulko.com>
To:     Miaohe Lin <linmiaohe@...wei.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Linux-MM <linux-mm@...ck.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 2/9] mm/z3fold: fix possible null pointer dereferencing

On Fri, Apr 29, 2022 at 8:40 AM Miaohe Lin <linmiaohe@...wei.com> wrote:
>
> alloc_slots could fail to allocate memory under heavy memory pressure. So
> we should check zhdr->slots against NULL to avoid future null pointer
> dereferencing.
>
> Fixes: fc5488651c7d ("z3fold: simplify freeing slots")
> Signed-off-by: Miaohe Lin <linmiaohe@...wei.com>
> ---
>  mm/z3fold.c | 12 +++++++++++-
>  1 file changed, 11 insertions(+), 1 deletion(-)
>
> diff --git a/mm/z3fold.c b/mm/z3fold.c
> index c2260f5a5885..5d8c21f2bc59 100644
> --- a/mm/z3fold.c
> +++ b/mm/z3fold.c
> @@ -940,9 +940,19 @@ static inline struct z3fold_header *__z3fold_alloc(struct z3fold_pool *pool,
>                 }
>         }
>
> -       if (zhdr && !zhdr->slots)
> +       if (zhdr && !zhdr->slots) {
>                 zhdr->slots = alloc_slots(pool, GFP_ATOMIC);
> +               if (!zhdr->slots)
> +                       goto out_fail;
> +       }
>         return zhdr;
> +
> +out_fail:
> +       if (!kref_put(&zhdr->refcount, release_z3fold_page_locked)) {
> +               add_to_unbuddied(pool, zhdr);
> +               z3fold_page_unlock(zhdr);
> +       }
> +       return NULL;
>  }

Reviewed-by: Vitaly Wool <vitaly.wool@...sulko.com>
>  /*
> --
> 2.23.0
>