Re: [Openvpn-devel] [PATCH v2 08/21] Decouple MSS fix calculation from frame calculation

[Frank Lichtenheld]

> Arne Schwabe <a...@rfc2549.org> hat am 14.12.2021 16:09 geschrieben:
> 
>  
> This consolidates the MSS fix calculation into a single function
> instead having it distributed all over the code. It also calculates
> the real wire overhead without extra sizes for buffer etc.
> 
> Patch v2: improve comment
> 
> Signed-off-by: Arne Schwabe <a...@rfc2549.org>
> ---
>  src/openvpn/forward.c |  5 ++---
>  src/openvpn/init.c    |  3 ++-
>  src/openvpn/mss.c     | 40 ++++++++++++++++++++++++++++++++++++++++
>  src/openvpn/mss.h     |  6 ++++++
>  src/openvpn/mtu.c     |  9 ---------
>  src/openvpn/mtu.h     | 10 ++++++----
>  src/openvpn/proto.h   | 11 -----------
>  src/openvpn/ssl.c     |  3 ++-
>  8 files changed, 58 insertions(+), 29 deletions(-)
> 
> diff --git a/src/openvpn/forward.c b/src/openvpn/forward.c
> index 29efcd3b9..f82386a1d 100644
> --- a/src/openvpn/forward.c
> +++ b/src/openvpn/forward.c
> @@ -1493,7 +1493,7 @@ process_ip_header(struct context *c, unsigned int 
> flags, struct buffer *buf)
>                  /* possibly alter the TCP MSS */
>                  if (flags & PIP_MSSFIX)
>                  {
> -                    mss_fixup_ipv4(&ipbuf, 
> MTU_TO_MSS(TUN_MTU_SIZE_DYNAMIC(&c->c2.frame)));
> +                    mss_fixup_ipv4(&ipbuf, c->c2.frame.mss_fix);

I still think this will badly explode in the ce.mssfix == 0 code path. In that 
case frame.mss_fix == 0 AFAICT
and I see no handling of that possibility in mss_fixup_ipv4/6.

Regards,
--
Frank Lichtenheld


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