[QUIC] padding of Initial packets

[Andrey Kolyshkin]

Hello.

This patch is strange.
1. ngx_quic_revert_send can set to ctx an uninitialized value from
preserved_pnum. (example if min > len and i = 0, only 0 element is filled
in preserved_pnum but restored all)
2. ngx_quic_revert_send will restored pnum for ctx that have already called
ngx_quic_output_packet and the packet with this pnum will be queued.
(example if min > len and i = 1)


On Wed, Feb 2, 2022 at 2:07 PM Sergey Kandaurov <pluknet at nginx.com> wrote:

>
> > On 2 Feb 2022, at 13:55, Vladimir Homutov <vl at nginx.com> wrote:
> >
> > # HG changeset patch
> > # User Vladimir Homutov <vl at nginx.com>
> > # Date 1643796973 -10800
> > #      Wed Feb 02 13:16:13 2022 +0300
> > # Branch quic
> > # Node ID fbfbcf66990e8964bcf308f3869f37d1a1acceeb
> > # Parent  8c6645ecaeb6cbf27976fd9035440bfcab943117
> > QUIC: fixed padding of initial packets in case of limited path.
> >
> > Previously, non-padded initial packet could be sent as a result of the
> > following situation:
> >
> > - initial queue is not empty (so padding to 1200 is required)
> > - handhsake queue is not empty (so padding is to be added after h/s
> packet)
>
> handshake
>
> > - path is limited
> >
> > If serializing handshake packet would violate path limit, such packet was
> > omitted, and the non-padded initial packet was sent.
> >
> > The fix is to avoid sending the packet at all in such case.  This
> follows the
> > original intention introduced in c5155a0cb12f.
> >
> > diff --git a/src/event/quic/ngx_event_quic_output.c
> b/src/event/quic/ngx_event_quic_output.c
> > --- a/src/event/quic/ngx_event_quic_output.c
> > +++ b/src/event/quic/ngx_event_quic_output.c
> > @@ -158,7 +158,14 @@ ngx_quic_create_datagrams(ngx_connection
> >                   ? NGX_QUIC_MIN_INITIAL_SIZE - (p - dst) : 0;
> >
> >             if (min > len) {
> > -                continue;
> > +                /* padding can't be applied - avoid sending the packet
> */
> > +
> > +                for (i = 0; i < NGX_QUIC_SEND_CTX_LAST; i++) {
> > +                    ctx = &qc->send_ctx[i];
> > +                    ngx_quic_revert_send(c, ctx, preserved_pnum[i]);
>
> this could be simplified to reduce ctx variable:
>     ngx_quic_revert_send(c, &qc->send_ctx[i], preserved_pnum[i]);
>
> but it won't fit into 80 line, so that's good just as well
>
> > +                }
> > +
> > +                return NGX_OK;
> >             }
> >
> >             n = ngx_quic_output_packet(c, ctx, p, len, min);
> >
>
> --
> Sergey Kandaurov
>
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>


-- 
Best regards, Andrey
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