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Date:   Wed, 26 Oct 2016 09:23:52 -0400
From:   Neil Horman <nhorman@...driver.com>
To:     Marcelo Ricardo Leitner <marcelo.leitner@...il.com>
Cc:     netdev@...r.kernel.org, linux-sctp@...r.kernel.org,
        Vlad Yasevich <vyasevich@...il.com>,
        syzkaller@...glegroups.com, kcc@...gle.com, glider@...gle.com,
        edumazet@...gle.com, dvyukov@...gle.com, andreyknvl@...gle.com
Subject: Re: [PATCH net] sctp: validate chunk len before actually using it

On Tue, Oct 25, 2016 at 02:27:39PM -0200, Marcelo Ricardo Leitner wrote:
> Andrey Konovalov reported that KASAN detected that SCTP was using a slab
> beyond the boundaries. It was caused because when handling out of the
> blue packets in function sctp_sf_ootb() it was checking the chunk len
> only after already processing the first chunk, validating only for the
> 2nd and subsequent ones.
> 
> The fix is to just move the check upwards so it's also validated for the
> 1st chunk.
> 
> Reported-by: Andrey Konovalov <andreyknvl@...gle.com>
> Tested-by: Andrey Konovalov <andreyknvl@...gle.com>
> Signed-off-by: Marcelo Ricardo Leitner <marcelo.leitner@...il.com>
> ---
> 
> Hi. Please consider this to -stable too. Thanks
> 
>  net/sctp/sm_statefuns.c | 12 ++++++------
>  1 file changed, 6 insertions(+), 6 deletions(-)
> 
> diff --git a/net/sctp/sm_statefuns.c b/net/sctp/sm_statefuns.c
> index 026e3bca4a94bd34b418d5e6947f7182c1512358..8ec20a64a3f8055a0c3576627c5ec5dad7e99ca8 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));
>  
> -- 
> 2.7.4
> 
> --
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> 
Acked-by: Neil Horman <nhorman@...driver.com>

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