resolved: basic OpenSSL support for DNS-over-TLS

This provides basic OpenSSL support without optimizations like TCP Fast Open and TLS Session Tickets.
Notice only a single SSL library can be enabled at a time and therefore journald functions provided by GnuTLS will be disabled when using OpenSSL.
Fixes #9531

1 files changed, 216 insertions, 0 deletions

diff --git a/src/resolve/resolved-dnstls-openssl.c b/src/resolve/resolved-dnstls-openssl.c
new file mode 100644
index 0000000000..d0a1bba773
--- /dev/null
+++ b/src/resolve/resolved-dnstls-openssl.c
@@ -0,0 +1,216 @@
+/* SPDX-License-Identifier: LGPL-2.1+ */
+
+#if !ENABLE_DNS_OVER_TLS || !DNS_OVER_TLS_USE_OPENSSL
+#error This source file requires DNS-over-TLS to be enabled and OpenSSL to be available.
+#endif
+
+#include "resolved-dnstls.h"
+#include "resolved-dns-stream.h"
+
+#include <openssl/bio.h>
+#include <openssl/err.h>
+
+DEFINE_TRIVIAL_CLEANUP_FUNC(SSL*, SSL_free);
+DEFINE_TRIVIAL_CLEANUP_FUNC(BIO*, BIO_free);
+
+int dnstls_stream_connect_tls(DnsStream *stream, DnsServer *server) {
+        _cleanup_(SSL_freep) SSL *s = NULL;
+        _cleanup_(BIO_freep) BIO *b = NULL;
+
+        assert(stream);
+        assert(server);
+
+        b = BIO_new_socket(stream->fd, 0);
+        if (!b)
+                return -ENOMEM;
+
+        s = SSL_new(server->dnstls_data.ctx);
+        if (!s)
+                return -ENOMEM;
+
+        SSL_set_connect_state(s);
+        SSL_set_bio(s, b, b);
+        b = NULL;
+
+        /* DNS-over-TLS using OpenSSL doesn't support TCP Fast Open yet */
+        connect(stream->fd, &stream->tfo_address.sa, stream->tfo_salen);
+        stream->tfo_salen = 0;
+
+        stream->encrypted = true;
+        stream->dnstls_events = EPOLLOUT;
+        stream->dnstls_data.ssl = TAKE_PTR(s);
+
+        return 0;
+}
+
+void dnstls_stream_free(DnsStream *stream) {
+        assert(stream);
+        assert(stream->encrypted);
+
+        if (stream->dnstls_data.ssl)
+                SSL_free(stream->dnstls_data.ssl);
+}
+
+int dnstls_stream_on_io(DnsStream *stream) {
+        int r;
+        int error;
+
+        assert(stream);
+        assert(stream->encrypted);
+        assert(stream->dnstls_data.ssl);
+
+        if (stream->dnstls_data.shutdown) {
+                r = SSL_shutdown(stream->dnstls_data.ssl);
+                if (r == 0)
+                        return -EAGAIN;
+                else if (r < 0) {
+                        error = SSL_get_error(stream->dnstls_data.ssl, r);
+                        if (IN_SET(error, SSL_ERROR_WANT_READ, SSL_ERROR_WANT_WRITE)) {
+                                stream->dnstls_events = error == SSL_ERROR_WANT_READ ? EPOLLIN : EPOLLOUT;
+                                return -EAGAIN;
+                        } else {
+                                char errbuf[256];
+
+                                ERR_error_string_n(error, errbuf, sizeof(errbuf));
+                                log_debug("Failed to invoke SSL_shutdown: %s", errbuf);
+                        }
+                }
+
+                stream->dnstls_events = 0;
+                stream->dnstls_data.shutdown = false;
+                dns_stream_unref(stream);
+                return DNSTLS_STREAM_CLOSED;
+        } else if (stream->dnstls_data.handshake <= 0) {
+                stream->dnstls_data.handshake = SSL_do_handshake(stream->dnstls_data.ssl);
+                if (stream->dnstls_data.handshake <= 0) {
+                        error = SSL_get_error(stream->dnstls_data.ssl, stream->dnstls_data.handshake);
+                        if (IN_SET(error, SSL_ERROR_WANT_READ, SSL_ERROR_WANT_WRITE)) {
+                                stream->dnstls_events = error == SSL_ERROR_WANT_READ ? EPOLLIN : EPOLLOUT;
+                                return -EAGAIN;
+                        } else {
+                                char errbuf[256];
+
+                                ERR_error_string_n(error, errbuf, sizeof(errbuf));
+                                log_debug("Failed to invoke SSL_do_handshake: %s", errbuf);
+                                return -ECONNREFUSED;
+                        }
+                }
+
+                stream->dnstls_events = 0;
+        }
+
+        return 0;
+}
+
+int dnstls_stream_shutdown(DnsStream *stream, int error) {
+        int r;
+        int ssl_error;
+        SSL_SESSION *s;
+
+        assert(stream);
+        assert(stream->encrypted);
+        assert(stream->dnstls_data.ssl);
+
+        if (error == ETIMEDOUT) {
+                r = SSL_shutdown(stream->dnstls_data.ssl);
+                if (r == 0) {
+                        if (!stream->dnstls_data.shutdown) {
+                                stream->dnstls_data.shutdown = true;
+                                dns_stream_ref(stream);
+                        }
+                        return -EAGAIN;
+                } else if (r < 0) {
+                        ssl_error = SSL_get_error(stream->dnstls_data.ssl, r);
+                        if (IN_SET(ssl_error, SSL_ERROR_WANT_READ, SSL_ERROR_WANT_WRITE)) {
+                                stream->dnstls_events = ssl_error == SSL_ERROR_WANT_READ ? EPOLLIN : EPOLLOUT;
+                                if (!stream->dnstls_data.shutdown) {
+                                        stream->dnstls_data.shutdown = true;
+                                        dns_stream_ref(stream);
+                                }
+                                return -EAGAIN;
+                        } else {
+                                char errbuf[256];
+
+                                ERR_error_string_n(ssl_error, errbuf, sizeof(errbuf));
+                                log_debug("Failed to invoke SSL_shutdown: %s", errbuf);
+                        }
+                }
+        }
+
+        return 0;
+}
+
+ssize_t dnstls_stream_write(DnsStream *stream, const char *buf, size_t count) {
+        int r;
+        int error;
+        ssize_t ss;
+
+        assert(stream);
+        assert(stream->encrypted);
+        assert(stream->dnstls_data.ssl);
+        assert(buf);
+
+        ss = r = SSL_write(stream->dnstls_data.ssl, buf, count);
+        if (r <= 0) {
+                error = SSL_get_error(stream->dnstls_data.ssl, ss);
+                if (IN_SET(error, SSL_ERROR_WANT_READ, SSL_ERROR_WANT_WRITE)) {
+                        stream->dnstls_events = error == SSL_ERROR_WANT_READ ? EPOLLIN : EPOLLOUT;
+                        ss = -EAGAIN;
+                } else {
+                        char errbuf[256];
+
+                        ERR_error_string_n(error, errbuf, sizeof(errbuf));
+                        log_debug("Failed to invoke SSL_read: %s", errbuf);
+                        ss = -EPIPE;
+                }
+        }
+
+        stream->dnstls_events = 0;
+        return ss;
+}
+
+ssize_t dnstls_stream_read(DnsStream *stream, void *buf, size_t count) {
+        int r;
+        int error;
+        ssize_t ss;
+
+        assert(stream);
+        assert(stream->encrypted);
+        assert(stream->dnstls_data.ssl);
+        assert(buf);
+
+        ss = r = SSL_read(stream->dnstls_data.ssl, buf, count);
+        if (r <= 0) {
+                error = SSL_get_error(stream->dnstls_data.ssl, ss);
+                if (IN_SET(error, SSL_ERROR_WANT_READ, SSL_ERROR_WANT_WRITE)) {
+                        stream->dnstls_events = error == SSL_ERROR_WANT_READ ? EPOLLIN : EPOLLOUT;
+                        ss = -EAGAIN;
+                } else {
+                        char errbuf[256];
+
+                        ERR_error_string_n(error, errbuf, sizeof(errbuf));
+                        log_debug("Failed to invoke SSL_read: %s", errbuf);
+                        ss = -EPIPE;
+                }
+        }
+
+        stream->dnstls_events = 0;
+        return ss;
+}
+
+void dnstls_server_init(DnsServer *server) {
+        assert(server);
+
+        server->dnstls_data.ctx = SSL_CTX_new(TLS_client_method());
+        if (server->dnstls_data.ctx) {
+                SSL_CTX_set_min_proto_version(server->dnstls_data.ctx, TLS1_2_VERSION);
+                SSL_CTX_set_options(server->dnstls_data.ctx, SSL_OP_NO_COMPRESSION);
+        }
+}
+
+void dnstls_server_free(DnsServer *server) {
+        assert(server);
+
+        if (server->dnstls_data.ctx)
+                SSL_CTX_free(server->dnstls_data.ctx);
+}