linux-kernel - Re: [PATCH] l2tp: Add protocol field decompression

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Message-Id: <20181215.232859.365899686560746192.davem@davemloft.net>
Date:   Sat, 15 Dec 2018 23:28:59 -0800 (PST)
From:   David Miller <davem@...emloft.net>
To:     semen.protsenko@...aro.org
Cc:     jchapman@...alix.com, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org, g.nault@...halink.fr
Subject: Re: [PATCH] l2tp: Add protocol field decompression

From: Sam Protsenko <semen.protsenko@...aro.org>
Date: Fri, 14 Dec 2018 19:59:21 +0200

> When Protocol Field Compression (PFC) is enabled, the "Protocol" field
> in PPP packet will be received without leading 0x00. See section 6.5 in
> RFC 1661 for details. So let's decompress protocol field if needed, the
> same way it's done in drivers/net/ppp/pptp.c.
> 
> In case when "nopcomp" pppd option is not enabled, PFC (pcomp) can be
> negotiated during LCP handshake, and L2TP driver in kernel will receive
> PPP packets with compressed Protocol field, which in turn leads to next
> error:
> 
>     Protocol Rejected (unsupported protocol 0x2145)
> 
> because instead of Protocol=0x0021 in PPP packet there will be
> Protocol=0x21. This patch unwraps it back to 0x0021, which fixes the
> issue.
> 
> Sending the compressed Protocol field will be implemented in subsequent
> patch, this one is self-sufficient.
> 
> Signed-off-by: Sam Protsenko <semen.protsenko@...aro.org>

Applied, thanks.