Stream connection cleanup handler ngx_quic_stream_cleanup_handler() calls
ngx_quic_shutdown_stream() after which it resets the pointer from quic stream
to the connection (sc->connection = NULL).  Previously if this call failed,
sc->connection retained the old value, while the connection was freed by the
application code.  This resulted later in a second attempt to close the freed
connection, which lead to allocator double free error.

The fix is to reset the sc->connection pointer in case of error.

Inspired by RFC 9001, Section 6.3, trial packet decryption with the current
keys is now used to avoid a timing side-channel signal.  Further, this fixes
segfault while accessing missing next keys (ticket #2585).

Previously if an MTU probe send failed early in ngx_quic_frame_sendto()
due to allocation error or congestion control, the application level packet
number was not increased, but was still saved as MTU probe packet number.
Later when a packet with this number was acknowledged, the unsent MTU probe
was acknowledged as well.  This could result in discovering a bigger MTU than
supported by the path, which could lead to EMSGSIZE (Message too long) errors
while sending further packets.

The problem existed since PMTUD was introduced in 58afcd72446f (1.25.2).
Back then only the unlikely memory allocation error could trigger it.  However
in efcdaa66df2e congestion control was added to ngx_quic_frame_sendto() which
can now trigger the issue with a higher probability.

Now "fastopen", "backlog", "accept_filter", "deferred", and "so_keepalive"
parameters are not allowed with "quic" in the "listen" directive.

Reported by Izorkin.

When filter finalization is triggered when working with an upstream server,
and error_page redirects request processing to some simple handler,
ngx_http_request_finalize() triggers request termination when the response
is sent.  In particular, via the upstream cleanup handler, nginx will close
the upstream connection and the corresponding socket.

Still, this can happen to be with ngx_event_pipe() on stack.  While
the code will set p->downstream_error due to NGX_ERROR returned from the
output filter chain by filter finalization, otherwise the error will be
ignored till control returns to ngx_http_upstream_process_request().
And event pipe might try reading from the (already closed) socket, resulting
in "readv() failed (9: Bad file descriptor) while reading upstream" errors
(or even segfaults with SSL).

Such errors were seen with the following configuration:

    location /t2 {
        proxy_pass http://127.0.0.1:8080/big;

        image_filter_buffer 10m;
        image_filter   resize  150 100;
        error_page     415   = /empty;
    }

    location /empty {
        return 204;
    }

    location /big {
        # big enough static file
    }

Fix is to clear p->upstream in ngx_http_upstream_finalize_request(),
and ensure that p->upstream is checked in ngx_event_pipe_read_upstream()
and when handling events at ngx_event_pipe() exit.

When a request was terminated due to an error via ngx_http_terminate_request()
while an AIO operation was running in a subrequest, various issues were
observed.  This happened because ngx_http_request_finalizer() was only set
in the subrequest where ngx_http_terminate_request() was called, but not
in the subrequest where the AIO operation was running.  After completion
of the AIO operation normal processing of the subrequest was resumed, leading
to issues.

In particular, in case of the upstream module, termination of the request
called upstream cleanup, which closed the upstream connection.  Attempts to
further work with the upstream connection after AIO operation completion
resulted in segfaults in ngx_ssl_recv(), "readv() failed (9: Bad file
descriptor) while reading upstream" errors, or socket leaks.

In ticket #2555, issues were observed with the following configuration
with cache background update (with thread writing instrumented to
introduce a delay, when a client closes the connection during an update):

    location = /background-and-aio-write {
        proxy_pass ...
        proxy_cache one;
        proxy_cache_valid 200 1s;
        proxy_cache_background_update on;
        proxy_cache_use_stale updating;
        aio threads;
        aio_write on;
        limit_rate 1000;
    }

Similarly, the same issue can be seen with SSI, and can be caused by
errors in subrequests, such as in the following configuration
(where "/proxy" uses AIO, and "/sleep" returns 444 after some delay,
causing request termination):

    location = /ssi-active-boom {
        ssi on;
        ssi_types *;
        return 200 '
                   <!--#include virtual="/proxy" -->
                   <!--#include virtual="/sleep" -->
                   ';
        limit_rate 1000;
    }

Or the same with both AIO operation and the error in non-active subrequests
(which needs slightly different handling, see below):

    location = /ssi-non-active-boom {
        ssi on;
        ssi_types *;
        return 200 '
                   <!--#include virtual="/static" -->
                   <!--#include virtual="/proxy" -->
                   <!--#include virtual="/sleep" -->
                   ';
        limit_rate 1000;
    }

Similarly, issues can be observed with just static files.  However,
with static files potential impact is limited due to timeout safeguards
in ngx_http_writer(), and the fact that c->error is set during request
termination.

In a simple configuration with an AIO operation in the active subrequest,
such as in the following configuration, the connection is closed right
after completion of the AIO operation anyway, since ngx_http_writer()
tries to write to the connection and fails due to c->error set:

    location = /ssi-active-static-boom {
        ssi on;
        ssi_types *;
        return 200 '
                   <!--#include virtual="/static-aio" -->
                   <!--#include virtual="/sleep" -->
                   ';
        limit_rate 1000;
    }

In the following configuration, with an AIO operation in a non-active
subrequest, the connection is closed only after send_timeout expires:

    location = /ssi-non-active-static-boom {
        ssi on;
        ssi_types *;
        return 200 '
                   <!--#include virtual="/static" -->
                   <!--#include virtual="/static-aio" -->
                   <!--#include virtual="/sleep" -->
                   ';
        limit_rate 1000;
    }

Fix is to introduce r->main->terminated flag, which is to be checked
by AIO event handlers when the r->main->blocked counter is decremented.
When the flag is set, handlers are expected to wake up the connection
instead of the subrequest (which might be already cleaned up).

Additionally, now ngx_http_request_finalizer() is always set in the
active subrequest, so waking up the connection properly finalizes the
request even if termination happened in a non-active subrequest.