Re: [Openvpn-devel] [PATCH 1/9] Indicate that a client is in pull mode in IV_PROTO

[Steffan K. <ste...@fo...>]

Hi,

On 17-07-2020 15:47, Arne Schwabe wrote:
> This allows us to skip waiting for the first PUSH_REQUEST message from
> the client to send the response.

Feature-ACK, clever use of existing infra. Some comments though:

This commit message could use a bit more information. In particular, it
would be good to explain how the various OpenVPN versions currently
interpret IV_PROTO values, and why the change from a version-like
interpretation to a bitfield will not cause issues.

> Signed-off-by: Arne Schwabe <ar...@rf...>
> ---
>  src/openvpn/multi.c | 12 ++++++++++--
>  src/openvpn/ssl.c   | 15 +++++++++++++--
>  src/openvpn/ssl.h   |  7 +++++++
>  3 files changed, 30 insertions(+), 4 deletions(-)
> 
> diff --git a/src/openvpn/multi.c b/src/openvpn/multi.c
> index 0095c871..88ba9db2 100644
> --- a/src/openvpn/multi.c
> +++ b/src/openvpn/multi.c
> @@ -1795,10 +1795,18 @@ multi_client_set_protocol_options(struct context *c)
>      {
>          int proto = 0;
>          int r = sscanf(optstr, "IV_PROTO=%d", &proto);
> -        if ((r == 1) && (proto >= 2))
> +        if (r == 1)
>          {
> -            tls_multi->use_peer_id = true;
> +            if (proto >= 2)
> +            {
> +                tls_multi->use_peer_id = true;
> +            }

Wouldn't checking for proto & IV_PROTO_REQUEST_PUSH suffice? Any 2.3/2.4
client will only ever send "2", and newer clients will know this is a
bitfield now.

This works fine, but - in particular without an explaining comment -
first checking for a value, then continue as a bitfield is somewhat
surprising.

> +            if (proto & IV_PROTO_REQUEST_PUSH)
> +            {
> +                c->c2.push_request_received = true;
> +            }
>          }
> +
>      }
>  
>      /* Select cipher if client supports Negotiable Crypto Parameters */
> diff --git a/src/openvpn/ssl.c b/src/openvpn/ssl.c
> index 54a23011..04d78a81 100644
> --- a/src/openvpn/ssl.c
> +++ b/src/openvpn/ssl.c
> @@ -2299,8 +2299,19 @@ push_peer_info(struct buffer *buf, struct tls_session *session)
>          buf_printf(&out, "IV_PLAT=win\n");
>  #endif
>  
> -        /* support for P_DATA_V2 */
> -        buf_printf(&out, "IV_PROTO=2\n");
> +        /* support for P_DATA_V2*/
> +        int iv_proto = IV_PROTO_DATA_V2;
> +
> +        /* support for receiving push_reply before sending
> +         * push request, also signal that the client wants
> +         * to get push-reply messages without without requiring a round
> +         * trip for a push request message*/
> +        if(session->opt->pull)

This needs a space behind the if.

> +        {
> +            iv_proto |= IV_PROTO_REQUEST_PUSH;
> +        }
> +
> +        buf_printf(&out, "IV_PROTO=%d\n", iv_proto);
>  
>          /* support for Negotiable Crypto Parameters */
>          if (session->opt->ncp_enabled
> diff --git a/src/openvpn/ssl.h b/src/openvpn/ssl.h
> index 58a9b0d4..86fb6853 100644
> --- a/src/openvpn/ssl.h
> +++ b/src/openvpn/ssl.h
> @@ -99,6 +99,13 @@
>  /* Maximum length of OCC options string passed as part of auth handshake */
>  #define TLS_OPTIONS_LEN 512
>  
> +/* Definitions of the bits in the IV_PROTO bitfield */
> +#define IV_PROTO_DATA_V2        (1<<1)  /**< Support P_DATA_V2 */
> +#define IV_PROTO_REQUEST_PUSH   (1<<2)  /**< Assume client will send a push
> +                                          * request and server does not need
> +                                          * to wait for a push-request to send
> +                                          * a push-reply */
> +

Style nit: would this not be more readable if you place the (rather
long) comment above the value, instead of behind?

Also: any particular reason to no use 1<<0 ? If we should not use that
for some reason, let's mark it as reserved. Otherwise: maybe just use it?

-Steffan