netdev - Re: net/sctp: slab-out-of-bounds in sctp_sf

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Message-ID: <CAAeHK+wSgHkk+pkTr+fp1jhA6XgaD+LoCmzAUWcdJKed=4A_PA@mail.gmail.com>
Date:   Tue, 25 Oct 2016 14:23:48 +0200
From:   Andrey Konovalov <andreyknvl@...gle.com>
To:     Marcelo Ricardo Leitner <marcelo.leitner@...il.com>
Cc:     Vlad Yasevich <vyasevich@...il.com>,
        Neil Horman <nhorman@...driver.com>,
        "David S. Miller" <davem@...emloft.net>,
        linux-sctp@...r.kernel.org, netdev <netdev@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        syzkaller <syzkaller@...glegroups.com>,
        Kostya Serebryany <kcc@...gle.com>,
        Alexander Potapenko <glider@...gle.com>,
        Eric Dumazet <edumazet@...gle.com>,
        Dmitry Vyukov <dvyukov@...gle.com>
Subject: Re: net/sctp: slab-out-of-bounds in sctp_sf_ootb

Hi Marcelo,

I can confirm that your patch fixes the issue for me.

Tested-by: Andrey Konovalov <andreyknvl@...gle.com>

On Mon, Oct 24, 2016 at 9:44 PM, Marcelo Ricardo Leitner
<marcelo.leitner@...il.com> wrote:
> Hi Andrey,
>
> On Mon, Oct 24, 2016 at 05:30:04PM +0200, Andrey Konovalov wrote:
>> The problem is that sctp_walk_errors walks the chunk before its length
>> is checked for overflow.
>
> Exactly. The check is done too late, for the 2nd and subsequent chunks
> only.
> Please try the following patch, thanks. Note: not even compile tested.
>
> ---8<---
>
> diff --git a/net/sctp/sm_statefuns.c b/net/sctp/sm_statefuns.c
> index 026e3bca4a94..8ec20a64a3f8 100644
> --- a/net/sctp/sm_statefuns.c
> +++ b/net/sctp/sm_statefuns.c
> @@ -3422,6 +3422,12 @@ sctp_disposition_t sctp_sf_ootb(struct net *net,
>                         return sctp_sf_violation_chunklen(net, ep, asoc, type, arg,
>                                                   commands);
>
> +               /* Report violation if chunk len overflows */
> +               ch_end = ((__u8 *)ch) + SCTP_PAD4(ntohs(ch->length));
> +               if (ch_end > skb_tail_pointer(skb))
> +                       return sctp_sf_violation_chunklen(net, ep, asoc, type, arg,
> +                                                 commands);
> +
>                 /* Now that we know we at least have a chunk header,
>                  * do things that are type appropriate.
>                  */
> @@ -3453,12 +3459,6 @@ sctp_disposition_t sctp_sf_ootb(struct net *net,
>                         }
>                 }
>
> -               /* Report violation if chunk len overflows */
> -               ch_end = ((__u8 *)ch) + SCTP_PAD4(ntohs(ch->length));
> -               if (ch_end > skb_tail_pointer(skb))
> -                       return sctp_sf_violation_chunklen(net, ep, asoc, type, arg,
> -                                                 commands);
> -
>                 ch = (sctp_chunkhdr_t *) ch_end;
>         } while (ch_end < skb_tail_pointer(skb));
>