Re: net/sctp: slab-out-of-bounds in sctp_sf_ootb

[Andrey Konovalov]

Hi Marcelo,

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

Tested-by: Andrey Konovalov <andreyknvl@xxxxxxxxxx>

On Mon, Oct 24, 2016 at 9:44 PM, Marcelo Ricardo Leitner
<marcelo.leitner@xxxxxxxxx> 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));
>