netdev - Re: [PATCH] sctp: account stream padding length for reconf chunk

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Date:   Tue, 12 Oct 2021 00:17:08 +0000
From:   Eiichi Tsukata <eiichi.tsukata@...anix.com>
To:     Marcelo Ricardo Leitner <marcelo.leitner@...il.com>
CC:     Greg KH <gregkh@...uxfoundation.org>,
        Vlad Yasevich <vyasevich@...il.com>,
        Neil Horman <nhorman@...driver.com>,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        "linux-sctp@...r.kernel.org" <linux-sctp@...r.kernel.org>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>
Subject: Re: [PATCH] sctp: account stream padding length for reconf chunk

Hi Marcelo

> On Oct 11, 2021, at 22:15, Marcelo Ricardo Leitner <marcelo.leitner@...il.com> wrote:
> 
> 
...
> 
> So if stream_num was originally 1, stream_len would be 2, and with
> padding, 4. Here, nums would be 2 then, and not 1. The padding gets
> accounted as if it was payload.
> 
> IOW, the patch is making the padding part of the parameter data by
> adding it to the header as well. SCTP padding works by having it in
> between them, and not inside them.
> 
> This other approach avoids this issue by adding the padding only when
> allocating the packet. It (ab)uses the fact that inreq and outreq are
> already aligned to 4 bytes. Eiichi, can you please give it a go?
> 
> 

Thanks, I understood. I’ve tested your diff with my reproducer and it certainly works.
Your diff looks good to me.

> 
> ---8<---
> 
> diff --git a/net/sctp/sm_make_chunk.c b/net/sctp/sm_make_chunk.c
> index b8fa8f1a7277..c7503fd64915 100644
> --- a/net/sctp/sm_make_chunk.c
> +++ b/net/sctp/sm_make_chunk.c
> @@ -3697,7 +3697,7 @@ struct sctp_chunk *sctp_make_strreset_req(
> 	outlen = (sizeof(outreq) + stream_len) * out;
> 	inlen = (sizeof(inreq) + stream_len) * in;
> 
> -	retval = sctp_make_reconf(asoc, outlen + inlen);
> +	retval = sctp_make_reconf(asoc, SCTP_PAD4(outlen) + SCTP_PAD4(inlen));
> 	if (!retval)
> 		return NULL;

Regards,

Eiichi