resolved: refactor GnuTLS specific code in separate source file

This is a first step towards supporting alternative TLS implementations for DNS-over-TLS.

Co-authored-by: Filipe Brandenburger <filbranden@google.com>

1 files changed, 198 insertions, 0 deletions

diff --git a/src/resolve/resolved-dnstls-gnutls.c b/src/resolve/resolved-dnstls-gnutls.c
new file mode 100644
index 0000000000..9c348cef67
--- /dev/null
+++ b/src/resolve/resolved-dnstls-gnutls.c
@@ -0,0 +1,198 @@
+/* SPDX-License-Identifier: LGPL-2.1+ */
+
+#if !ENABLE_DNS_OVER_TLS || !HAVE_GNUTLS
+#error This source file requires DNS-over-TLS to be enabled and GnuTLS to be available.
+#endif
+
+#include "resolved-dnstls.h"
+#include "resolved-dns-stream.h"
+
+#include <gnutls/socket.h>
+
+DEFINE_TRIVIAL_CLEANUP_FUNC(gnutls_session_t, gnutls_deinit);
+
+static ssize_t dnstls_stream_writev(gnutls_transport_ptr_t p, const giovec_t *iov, int iovcnt) {
+        int r;
+
+        assert(p);
+
+        r = dns_stream_writev((DnsStream*) p, (const struct iovec*) iov, iovcnt, DNS_STREAM_WRITE_TLS_DATA);
+        if (r < 0) {
+                errno = -r;
+                return -1;
+        }
+
+        return r;
+}
+
+int dnstls_stream_connect_tls(DnsStream *stream, DnsServer *server) {
+        _cleanup_(gnutls_deinitp) gnutls_session_t gs;
+        int r;
+
+        assert(stream);
+        assert(server);
+
+        r = gnutls_init(&gs, GNUTLS_CLIENT | GNUTLS_ENABLE_FALSE_START | GNUTLS_NONBLOCK);
+        if (r < 0)
+                return r;
+
+        /* As DNS-over-TLS is a recent protocol, older TLS versions can be disabled */
+        r = gnutls_priority_set_direct(gs, "NORMAL:-VERS-ALL:+VERS-TLS1.2", NULL);
+        if (r < 0)
+                return r;
+
+        r = gnutls_credentials_set(gs, GNUTLS_CRD_CERTIFICATE, server->dnstls_data.cert_cred);
+        if (r < 0)
+                return r;
+
+        if (server->dnstls_data.session_data.size > 0) {
+                gnutls_session_set_data(gs, server->dnstls_data.session_data.data, server->dnstls_data.session_data.size);
+
+                // Clear old session ticket
+                gnutls_free(server->dnstls_data.session_data.data);
+                server->dnstls_data.session_data.data = NULL;
+                server->dnstls_data.session_data.size = 0;
+        }
+
+        gnutls_handshake_set_timeout(gs, GNUTLS_DEFAULT_HANDSHAKE_TIMEOUT);
+
+        gnutls_transport_set_ptr2(gs, (gnutls_transport_ptr_t) (long) stream->fd, stream);
+        gnutls_transport_set_vec_push_function(gs, &dnstls_stream_writev);
+
+        stream->encrypted = true;
+        stream->dnstls_data.handshake = gnutls_handshake(gs);
+        if (stream->dnstls_data.handshake < 0 && gnutls_error_is_fatal(stream->dnstls_data.handshake))
+                return -ECONNREFUSED;
+
+        stream->dnstls_data.session = TAKE_PTR(gs);
+
+        return 0;
+}
+
+void dnstls_stream_free(DnsStream *stream) {
+        assert(stream);
+        assert(stream->encrypted);
+
+        if (stream->dnstls_data.session)
+                gnutls_deinit(stream->dnstls_data.session);
+}
+
+int dnstls_stream_on_io(DnsStream *stream) {
+        int r;
+
+        assert(stream);
+        assert(stream->encrypted);
+        assert(stream->dnstls_data.session);
+
+        if (stream->dnstls_data.shutdown) {
+                r = gnutls_bye(stream->dnstls_data.session, GNUTLS_SHUT_RDWR);
+                if (r == GNUTLS_E_AGAIN)
+                        return -EAGAIN;
+                else if (r < 0)
+                        log_debug("Failed to invoke gnutls_bye: %s", gnutls_strerror(r));
+
+                stream->dnstls_data.shutdown = false;
+                dns_stream_unref(stream);
+                return DNSTLS_STREAM_CLOSED;
+        } else if (stream->dnstls_data.handshake < 0) {
+                stream->dnstls_data.handshake = gnutls_handshake(stream->dnstls_data.session);
+                if (stream->dnstls_data.handshake == GNUTLS_E_AGAIN)
+                        return -EAGAIN;
+                else if (stream->dnstls_data.handshake < 0) {
+                        log_debug("Failed to invoke gnutls_handshake: %s", gnutls_strerror(stream->dnstls_data.handshake));
+                        if (gnutls_error_is_fatal(stream->dnstls_data.handshake))
+                                return -ECONNREFUSED;
+                }
+        }
+
+        return 0;
+}
+
+int dnstls_stream_shutdown(DnsStream *stream, int error) {
+        int r;
+
+        assert(stream);
+        assert(stream->encrypted);
+        assert(stream->dnstls_data.session);
+
+        /* Store TLS Ticket for faster succesive TLS handshakes */
+        if (stream->server && stream->server->dnstls_data.session_data.size == 0 && stream->dnstls_data.handshake == GNUTLS_E_SUCCESS)
+                gnutls_session_get_data2(stream->dnstls_data.session, &stream->server->dnstls_data.session_data);
+
+        if (IN_SET(error, ETIMEDOUT, 0)) {
+                r = gnutls_bye(stream->dnstls_data.session, GNUTLS_SHUT_RDWR);
+                if (r == GNUTLS_E_AGAIN) {
+                        if (!stream->dnstls_data.shutdown) {
+                                stream->dnstls_data.shutdown = true;
+                                dns_stream_ref(stream);
+                                return -EAGAIN;
+                        }
+                } else if (r < 0)
+                        log_debug("Failed to invoke gnutls_bye: %s", gnutls_strerror(r));
+        }
+
+        return 0;
+}
+
+ssize_t dnstls_stream_write(DnsStream *stream, const char *buf, size_t count) {
+        ssize_t ss;
+
+        assert(stream);
+        assert(stream->encrypted);
+        assert(stream->dnstls_data.session);
+        assert(buf);
+
+        ss = gnutls_record_send(stream->dnstls_data.session, buf, count);
+        if (ss < 0)
+                switch(ss) {
+                case GNUTLS_E_INTERRUPTED:
+                        return -EINTR;
+                case GNUTLS_E_AGAIN:
+                        return -EAGAIN;
+                default:
+                        log_debug("Failed to invoke gnutls_record_send: %s", gnutls_strerror(ss));
+                        return -EPIPE;
+                }
+
+        return ss;
+}
+
+ssize_t dnstls_stream_read(DnsStream *stream, void *buf, size_t count) {
+        ssize_t ss;
+
+        assert(stream);
+        assert(stream->encrypted);
+        assert(stream->dnstls_data.session);
+        assert(buf);
+
+        ss = gnutls_record_recv(stream->dnstls_data.session, buf, count);
+        if (ss < 0)
+                switch(ss) {
+                case GNUTLS_E_INTERRUPTED:
+                        return -EINTR;
+                case GNUTLS_E_AGAIN:
+                        return -EAGAIN;
+                default:
+                        log_debug("Failed to invoke gnutls_record_recv: %s", gnutls_strerror(ss));
+                        return -EPIPE;
+                }
+
+        return ss;
+}
+
+void dnstls_server_init(DnsServer *server) {
+        assert(server);
+
+        /* Do not verify cerificate */
+        gnutls_certificate_allocate_credentials(&server->dnstls_data.cert_cred);
+}
+
+void dnstls_server_free(DnsServer *server) {
+        assert(server);
+
+        if (server->dnstls_data.cert_cred)
+                gnutls_certificate_free_credentials(server->dnstls_data.cert_cred);
+
+        if (server->dnstls_data.session_data.data)
+                gnutls_free(server->dnstls_data.session_data.data);
+}