feature: ngx_http_lua_ffi_ssl_set_ciphers().

Sets the connection's TLS <= 1.2 cipher list and/or TLS 1.3 ciphersuites
from ssl_client_hello_by_lua*, e.g. keyed on the client hello server name.

Both strings are validated on a scratch SSL_CTX before being applied to
the connection, because a failed SSL_set_cipher_list() still installs the
parsed list on the connection (emptying the TLS <= 1.2 list on unknown
tokens) and leaves the thread error queue dirty, which makes
SSL_do_handshake() report failure after the callback returns.

The guarantee: if ngx_http_lua_ffi_ssl_set_ciphers returns NGX_ERROR for
an invalid ciphers and/or ciphersuites string, the connection's SSL
object is left exactly as it was -- cipher list, ciphersuites, and thread
error queue all untouched -- so the handshake proceeds with whatever the
connection already had, which is the default list inherited from the
vhost's SSL_CTX (ssl_ciphers/ssl_conf_command).

See openssl/openssl#7759 for the check-after-
install behaviour of SSL_set_cipher_list() and
https://docs.openssl.org/3.0/man3/SSL_get_error/ for the empty-queue
requirement.

Author: climagabriel

src/ngx_http_lua_ssl_client_helloby.c

@@ -838,4 +838,85 @@ ngx_http_lua_ffi_ssl_set_protocols(ngx_http_request_t *r,
     return NGX_OK;
 }
 
+
+int
+ngx_http_lua_ffi_ssl_set_ciphers(ngx_http_request_t *r, const char *ciphers,
+    const char *ciphersuites, char **err)
+{
+#ifdef SSL_ERROR_WANT_CLIENT_HELLO_CB
+    ngx_ssl_conn_t     *ssl_conn;
+
+    static SSL_CTX     *scratch_ctx;
+
+    if (r->connection == NULL || r->connection->ssl == NULL) {
+        *err = "bad request";
+        return NGX_ERROR;
+    }
+
+    ssl_conn = r->connection->ssl->connection;
+    if (ssl_conn == NULL) {
+        *err = "bad ssl conn";
+        return NGX_ERROR;
+    }
+
+    /*
+     * a failed SSL_set_cipher_list() still installs the parsed list on the
+     * connection and leaves the error queue dirty, which aborts the
+     * handshake after the callback returns; validate on a scratch SSL_CTX
+     * so failure is side-effect-free and callers can fall back to the
+     * connection default
+     */
+
+    if (scratch_ctx == NULL) {
+        scratch_ctx = SSL_CTX_new(TLS_method());
+        if (scratch_ctx == NULL) {
+            ERR_clear_error();
+            *err = "SSL_CTX_new() failed";
+            return NGX_ERROR;
+        }
+    }
+
+    if (ciphers != NULL && *ciphers != '\0') {
+        if (SSL_CTX_set_cipher_list(scratch_ctx, ciphers) == 0) {
+            ERR_clear_error();
+            *err = "SSL_set_cipher_list() failed";
+            return NGX_ERROR;
+        }
+    }
+
+#ifdef TLS1_3_VERSION
+    if (ciphersuites != NULL && *ciphersuites != '\0') {
+        if (SSL_CTX_set_ciphersuites(scratch_ctx, ciphersuites) == 0) {
+            ERR_clear_error();
+            *err = "SSL_set_ciphersuites() failed";
+            return NGX_ERROR;
+        }
+    }
+#endif
+
+    if (ciphers != NULL && *ciphers != '\0') {
+        if (SSL_set_cipher_list(ssl_conn, ciphers) == 0) {
+            ERR_clear_error();
+            *err = "SSL_set_cipher_list() failed";
+            return NGX_ERROR;
+        }
+    }
+
+#ifdef TLS1_3_VERSION
+    if (ciphersuites != NULL && *ciphersuites != '\0') {
+        if (SSL_set_ciphersuites(ssl_conn, ciphersuites) == 0) {
+            ERR_clear_error();
+            *err = "SSL_set_ciphersuites() failed";
+            return NGX_ERROR;
+        }
+    }
+#endif
+
+    return NGX_OK;
+#else
+    *err = "OpenSSL too old to support this function";
+    return NGX_ERROR;
+#endif
+}
+
 #endif /* NGX_HTTP_SSL */