[quic] ngx_quic_input_handler Segmentation fault because c->udp->dgram is null

[Vladimir Homutov]

On Thu, Jan 27, 2022 at 04:33:08AM +0000, Gao,Yan(媒体云) wrote:
> > The main quic connection is created in ngx_quic_new_connection(), which
> > calls ngx_quic_open_sockets() and it sets c->udp for the first time.
>
> > When packet arrives, c->udp is updated by ngx_lookup_udp_connection().
>
> > The main connection does not have c->quic set; this is used in stream
> > connections. To access main connection from quic stream, c->quic->parent
> > may be used.
>
> ngx_event_recvmsg->(ls->handler) ngx_http_init_connection->ngx_http_v3_init:
>     if (c->quic == NULL) {
>         h3scf->quic.timeout = clcf->keepalive_timeout;
>         ngx_quic_run(c, &h3scf->quic);
>         return;
> }
>
> And, why check c->quic == NULL, as it is never set

first time you get there with main nginx connection, when a first QUIC
packet arrives. Thus test c->quic. and if it is NULL it means we need
to create main quic connection and proceed with the handshake.

When the handshake is complete, a stream will be created, and the
ngx_quic_init_stream_handler() will be called which will invoke
listening handler, and we will return into ngx_http_v3_init() with
stream connection that has c->quic set and follow the other path.