[PATCH 6 of 6] QUIC: path revalidation after expansion failure

[Sergey Kandaurov]

> On 30 Nov 2023, at 15:05, Roman Arutyunyan <arut at nginx.com> wrote:
> 
> # HG changeset patch
> # User Roman Arutyunyan <arut at nginx.com>
> # Date 1701241101 -14400
> #      Wed Nov 29 10:58:21 2023 +0400
> # Node ID 82fa5941af6fecb4fc7f0ac6308ae6c266d5e545
> # Parent  4b7663d9146ce9baeb78fb57c3fed7368f25dae9
> QUIC: path revalidation after expansion failure.
> 
> As per RFC 9000, Section 8.2.1:
> 
>    When an endpoint is unable to expand the datagram size to 1200 bytes due
>    to the anti-amplification limit, the path MTU will not be validated.
>    To ensure that the path MTU is large enough, the endpoint MUST perform a
>    second path validation by sending a PATH_CHALLENGE frame in a datagram of
>    at least 1200 bytes.
> 
> diff --git a/src/event/quic/ngx_event_quic_connection.h b/src/event/quic/ngx_event_quic_connection.h
> --- a/src/event/quic/ngx_event_quic_connection.h
> +++ b/src/event/quic/ngx_event_quic_connection.h
> @@ -111,7 +111,8 @@ struct ngx_quic_path_s {
>     uint64_t                          mtu_pnum[NGX_QUIC_PATH_RETRIES];
>     ngx_str_t                         addr_text;
>     u_char                            text[NGX_SOCKADDR_STRLEN];
> -    ngx_uint_t                        validated; /* unsigned validated:1; */
> +    unsigned                          validated:1;
> +    unsigned                          mtu_unvalidated:1;
> };
> 
> 
> diff --git a/src/event/quic/ngx_event_quic_migration.c b/src/event/quic/ngx_event_quic_migration.c
> --- a/src/event/quic/ngx_event_quic_migration.c
> +++ b/src/event/quic/ngx_event_quic_migration.c
> @@ -169,6 +169,7 @@ valid:
> 
>             path->mtu = prev->mtu;
>             path->max_mtu = prev->max_mtu;
> +            path->mtu_unvalidated = 0;
>         }
>     }
> 
> @@ -182,6 +183,13 @@ valid:
>         qc->congestion.recovery_start = ngx_current_msec;
>     }
> 
> +    path->validated = 1;
> +
> +    if (path->mtu_unvalidated) {
> +        path->mtu_unvalidated = 0;
> +        return ngx_quic_validate_path(c, path);
> +    }
> +
>     /*
>      * RFC 9000, 9.3.  Responding to Connection Migration
>      *
> @@ -199,8 +207,6 @@ valid:
> 
>     ngx_quic_path_dbg(c, "is validated", path);
> 
> -    path->validated = 1;
> -
>     ngx_quic_discover_path_mtu(c, path);
> 
>     return NGX_OK;
> @@ -578,7 +584,15 @@ ngx_quic_send_path_challenge(ngx_connect
>          * sending a datagram of this size.
>          */
> 
> -        min = (ngx_quic_path_limit(c, path, 1200) < 1200) ? 0 : 1200;
> +        if (path->mtu_unvalidated
> +            || ngx_quic_path_limit(c, path, 1200) < 1200)
> +        {
> +            min = 0;
> +            path->mtu_unvalidated = 1;
> +
> +        } else {
> +            min = 1200;
> +        }
> 
>         if (ngx_quic_frame_sendto(c, frame, min, path) == NGX_ERROR) {
>             return NGX_ERROR;

This needs the following fixup, path->validated is now a bit-mask.

# HG changeset patch
# User Sergey Kandaurov <pluknet at nginx.com>
# Date 1702643887 -14400
#      Fri Dec 15 16:38:07 2023 +0400
# Node ID 763803589a36e3c67cbe39dd324b4e91fe57ecb7
# Parent  cbe1a0e8094be744b940fe1b0cc5314f99c94672
QUIC: fixed format specifier after a6f79f044de5.

diff --git a/src/event/quic/ngx_event_quic_migration.h b/src/event/quic/ngx_event_quic_migration.h
--- a/src/event/quic/ngx_event_quic_migration.h
+++ b/src/event/quic/ngx_event_quic_migration.h
@@ -19,7 +19,7 @@
 
 #define ngx_quic_path_dbg(c, msg, path)                                       \
     ngx_log_debug7(NGX_LOG_DEBUG_EVENT, c->log, 0,                            \
-                   "quic path seq:%uL %s tx:%O rx:%O valid:%ui st:%d mtu:%uz",\
+                   "quic path seq:%uL %s tx:%O rx:%O valid:%d st:%d mtu:%uz", \
                    path->seqnum, msg, path->sent, path->received,             \
                    path->validated, path->state, path->mtu);
 

-- 
Sergey Kandaurov