netdev - Re: [PATCH net] sctp: fix the check for _sctp_walk_params and _sctp_walk

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Date:   Wed, 26 Jul 2017 09:14:36 -0400
From:   Neil Horman <nhorman@...driver.com>
To:     Xin Long <lucien.xin@...il.com>
Cc:     network dev <netdev@...r.kernel.org>, linux-sctp@...r.kernel.org,
        davem@...emloft.net,
        Marcelo Ricardo Leitner <marcelo.leitner@...il.com>,
        glider@...gle.com
Subject: Re: [PATCH net] sctp: fix the check for _sctp_walk_params and
 _sctp_walk_errors

On Wed, Jul 26, 2017 at 04:24:59PM +0800, Xin Long wrote:
> Commit b1f5bfc27a19 ("sctp: don't dereference ptr before leaving
> _sctp_walk_{params, errors}()") tried to fix the issue that it
> may overstep the chunk end for _sctp_walk_{params, errors} with
> 'chunk_end > offset(length) + sizeof(length)'.
> 
> But it introduced a side effect: When processing INIT, it verifies
> the chunks with 'param.v == chunk_end' after iterating all params
> by sctp_walk_params(). With the check 'chunk_end > offset(length)
> + sizeof(length)', it would return when the last param is not yet
> accessed. Because the last param usually is fwdtsn supported param
> whose size is 4 and 'chunk_end == offset(length) + sizeof(length)'
> 
> This is a badly issue even causing sctp couldn't process 4-shakes.
> Client would always get abort when connecting to server, due to
> the failure of INIT chunk verification on server.
> 
> The patch is to use 'chunk_end <= offset(length) + sizeof(length)'
> instead of 'chunk_end < offset(length) + sizeof(length)' for both
> _sctp_walk_params and _sctp_walk_errors.
> 
> Fixes: b1f5bfc27a19 ("sctp: don't dereference ptr before leaving _sctp_walk_{params, errors}()")
> Signed-off-by: Xin Long <lucien.xin@...il.com>
> ---
>  include/net/sctp/sctp.h | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/include/net/sctp/sctp.h b/include/net/sctp/sctp.h
> index 980807d..45fd4c6 100644
> --- a/include/net/sctp/sctp.h
> +++ b/include/net/sctp/sctp.h
> @@ -469,7 +469,7 @@ _sctp_walk_params((pos), (chunk), ntohs((chunk)->chunk_hdr.length), member)
>  
>  #define _sctp_walk_params(pos, chunk, end, member)\
>  for (pos.v = chunk->member;\
> -     (pos.v + offsetof(struct sctp_paramhdr, length) + sizeof(pos.p->length) <\
> +     (pos.v + offsetof(struct sctp_paramhdr, length) + sizeof(pos.p->length) <=\
>        (void *)chunk + end) &&\
>       pos.v <= (void *)chunk + end - ntohs(pos.p->length) &&\
>       ntohs(pos.p->length) >= sizeof(struct sctp_paramhdr);\
> @@ -481,7 +481,7 @@ _sctp_walk_errors((err), (chunk_hdr), ntohs((chunk_hdr)->length))
>  #define _sctp_walk_errors(err, chunk_hdr, end)\
>  for (err = (sctp_errhdr_t *)((void *)chunk_hdr + \
>  	    sizeof(struct sctp_chunkhdr));\
> -     ((void *)err + offsetof(sctp_errhdr_t, length) + sizeof(err->length) <\
> +     ((void *)err + offsetof(sctp_errhdr_t, length) + sizeof(err->length) <=\
>        (void *)chunk_hdr + end) &&\
>       (void *)err <= (void *)chunk_hdr + end - ntohs(err->length) &&\
>       ntohs(err->length) >= sizeof(sctp_errhdr_t); \
> -- 
> 2.1.0
> 
> --
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> 
Acked-by: Neil Horman <nhorman@...driver.com>