linux-kernel - Re: [PATCH] mm: prevent page_frag_alloc() from corrupting the memory

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Message-ID: <CAFL455m0UAXwLd78Eh=Vq-H6sQTPdmGAOOt2rOM1XtRqsqH=bQ@mail.gmail.com>
Date:   Wed, 13 Jul 2022 17:01:38 +0200
From:   Maurizio Lombardi <mlombard@...hat.com>
To:     Alexander Duyck <alexander.duyck@...il.com>
Cc:     Jakub Kicinski <kuba@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        linux-mm <linux-mm@...ck.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Netdev <netdev@...r.kernel.org>,
        愚树 <chen45464546@....com>
Subject: Re: [PATCH] mm: prevent page_frag_alloc() from corrupting the memory

st 13. 7. 2022 v 16:59 odesílatel Maurizio Lombardi
<mlombard@...hat.com> napsal:
>
> A number of drivers call page_frag_alloc() with a
> fragment's size > PAGE_SIZE.
> In low memory conditions, __page_frag_cache_refill() may fail the order 3
> cache allocation and fall back to order 0;
> In this case, the cache will be smaller than the fragment, causing
> memory corruptions.

Oops, I didn't modify the subject, I'm going to resend it.

Maurizio

>
> Prevent this from happening by checking if the newly allocated cache
> is large enough for the fragment; if not, the allocation will fail
> and page_frag_alloc() will return NULL.
>
> V2: do not free the cache page because this could make memory pressure
> even worse, just return NULL.
>
> Signed-off-by: Maurizio Lombardi <mlombard@...hat.com>
> ---
>  mm/page_alloc.c | 2 ++
>  1 file changed, 2 insertions(+)
>
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index e008a3df0485..b1407254a826 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -5617,6 +5617,8 @@ void *page_frag_alloc_align(struct page_frag_cache *nc,
>                 /* reset page count bias and offset to start of new frag */
>                 nc->pagecnt_bias = PAGE_FRAG_CACHE_MAX_SIZE + 1;
>                 offset = size - fragsz;
> +               if (unlikely(offset < 0))
> +                       return NULL;
>         }
>
>         nc->pagecnt_bias--;
> --
> 2.31.1
>