The "no suitable signature algorithm" errors are reported by OpenSSL 1.1.1
when using TLSv1.3 if there are no shared signature algorithms.  In
particular, this can happen if the client limits available signature
algorithms to something we don't have a certificate for, or to an empty
list.  For example, the following command:

    openssl s_client -connect 127.0.0.1:8443 -sigalgs rsa_pkcs1_sha1

will always result in the "no suitable signature algorithm" error
as the "rsa_pkcs1_sha1" algorithm refers solely to signatures which
appear in certificates and not defined for use in TLS 1.3 handshake
messages.

The SSL_R_NO_COMMON_SIGNATURE_ALGORITHMS error is what BoringSSL returns
in the same situation.

The "no suitable key share" errors are reported by OpenSSL 1.1.1 when
using TLSv1.3 if there are no shared groups (that is, elliptic curves).
In particular, it is easy enough to trigger by using only a single
curve in ssl_ecdh_curve:

    ssl_ecdh_curve secp384r1;

and using a different curve in the client:

    openssl s_client -connect 127.0.0.1:443 -curves prime256v1

On the client side it is seen as "sslv3 alert handshake failure",
"SSL alert number 40":

0:error:14094410:SSL routines:ssl3_read_bytes:sslv3 alert handshake failure:ssl/record/rec_layer_s3.c:1528:SSL alert number 40

It can be also triggered with default ssl_ecdh_curve by using a curve
which is not in the default list (X25519, prime256v1, X448, secp521r1,
secp384r1):

    openssl s_client -connect 127.0.0.1:8443 -curves brainpoolP512r1

Given that many clients hardcode prime256v1, these errors might become
a common problem with TLSv1.3 if ssl_ecdh_curve is redefined.  Previously
this resulted in not using ECDH with such clients, but with TLSv1.3 it
is no longer possible and will result in a handshake failure.

The SSL_R_NO_SHARED_GROUP error is what BoringSSL returns in the same
situation.

Seen at:

https://serverfault.com/questions/932102/nginx-ssl-handshake-error-no-suitable-key-share

Previously, configurations with typo, for example

    fastcgi_cache_valid 200301 302 5m;

successfully pass configuration test. Adding check for status
codes > 599, and such configurations are now properly rejected.

The bgcolor attribute overrides compatibility settings in browsers
and leads to undesirable behavior when the default font color is set
to white in the browser, since font-color is not also overridden.

In collaboration with Maxim Dounin.

Following 7319:dcab86115261, as long as SSL_OP_NO_RENEGOTIATION is
defined, it is OpenSSL library responsibility to prevent renegotiation,
so the checks are meaningless.

Additionally, with TLSv1.3 OpenSSL tends to report SSL_CB_HANDSHAKE_START
at various unexpected moments - notably, on KeyUpdate messages and
when sending tickets.  This change prevents unexpected connection
close on KeyUpdate messages and when finishing handshake with upcoming
early data changes.

Trying to look into r->err_status in the "return" directive
makes it behave differently than real errors generated in other
parts of the code, and is an endless source of various problems.
This behaviour was introduced in 726:7b71936d5299 (0.4.4) with
the comment "fix: "return" always overrode "error_page" response code".
It is not clear if there were any real cases this was expected to fix,
but there are several cases which are broken due to this change, some
previously fixed (4147:7f64de1cc2c0).

In ticket #1634, the problem is that when r->err_status is set to
a non-special status code, it is not possible to return a response
by simply returning r->err_status.  If this is the case, the only
option is to return script's e->status instead.  An example
configuration:

    location / {
        error_page 404 =200 /err502;
        return 404;
    }

    location = /err502 {
        return 502;
    }

After the change, such a configuration will properly return
standard 502 error, much like it happens when a 502 error is
generated by proxy_pass.

This also fixes the following configuration to properly close
connection as clearly requested by "return 444":

    location / {
        error_page 404 /close;
        return 404;
    }

    location = /close {
        return 444;
    }

Previously, this required "error_page 404 = /close;" to work
as intended.

Socket leak was observed in the following configuration:

    error_page 400 = /close;

    location = /close {
        return 444;
    }

The problem is that "return 444" triggers termination of the request,
and due to error_page termination thinks that it needs to use a posted
request to clear stack.  But at the early request processing where 400
errors are generated there are no ngx_http_run_posted_requests() calls,
so the request is only terminated after an external event.

Variants of the problem include "error_page 497" instead (ticket #695)
and various other errors generated during early request processing
(405, 414, 421, 494, 495, 496, 501, 505).

The same problem can be also triggered with "return 499" and "return 408"
as both codes trigger ngx_http_terminate_request(), much like "return 444".

To fix this, the patch adds ngx_http_run_posted_requests() calls to
ngx_http_process_request_line() and ngx_http_process_request_headers()
functions, and to ngx_http_v2_run_request() and ngx_http_v2_push_stream()
functions in HTTP/2.

Since the ngx_http_process_request() function is now only called via
other functions which call ngx_http_run_posted_requests(), the call
there is no longer needed and was removed.

It is possible that after SSL_read() will return SSL_ERROR_WANT_WRITE,
further calls will return SSL_ERROR_WANT_READ without reading any
application data.  We have to call ngx_handle_write_event() and
switch back to normal write handling much like we do if there are some
application data, or the write there will be reported again and again.

Similarly, we have to switch back to normal read handling if there
is saved read handler and SSL_write() returns SSL_ERROR_WANT_WRITE.