Merge fb437dc7ab into f70e5620b6

Add support for DNS-over-HTTPS (DoH) to resolved. The feature can be enabled
through the option DNSOverHTTPS. The implementation takes advantage of the
curl-util used by import tool, for that we move the curl-util to src/basic and
adjust import tool build settings.

meson.build

@@ -1579,6 +1579,29 @@ conf.set('DEFAULT_DNS_OVER_TLS_MODE',
          'DNS_OVER_TLS_' + default_dns_over_tls.underscorify().to_upper())
 conf.set_quoted('DEFAULT_DNS_OVER_TLS_MODE_STR', default_dns_over_tls)
 
+dns_over_https = get_option('dns-over-https')
+if dns_over_https != 'false'
+         have = true
+         if conf.get('HAVE_LIBCURL') == 0
+            message('DNS-over-HTTPS support depends on libcurl, but dependencies are not available')
+            have = false
+         endif
+         if conf.get('HAVE_OPENSSL') == 0
+            message('openssl required, but not available')
+            have = false
+         endif
+endif
+conf.set10('ENABLE_DNS_OVER_HTTPS', have)
+
+default_dns_over_https = get_option('default-dns-over-https')
+if default_dns_over_https != 'no' and conf.get('ENABLE_DNS_OVER_HTTPS') == 0
+        message('default-dns-over-https cannot be enabled. Setting default-dns-over-https to no.')
+        default_dns_over_https = 'no'
+endif
+conf.set('DEFAULT_DNS_OVER_HTTPS_MODE',
+         'DNS_OVER_HTTPS_' + default_dns_over_https.underscorify().to_upper())
+conf.set_quoted('DEFAULT_DNS_OVER_HTTPS_MODE_STR', default_dns_over_https)
+
 default_mdns = get_option('default-mdns')
 conf.set('DEFAULT_MDNS_MODE',
          'RESOLVE_SUPPORT_' + default_mdns.to_upper())
@@ -3002,6 +3025,7 @@ summary({
         'default compression method' :      compression,
         'default DNSSEC mode' :             default_dnssec,
         'default DNS-over-TLS mode' :       default_dns_over_tls,
+        'default DNS-over-HTTPS mode' :     default_dns_over_https,
         'default mDNS mode' :               default_mdns,
         'default LLMNR mode' :              default_llmnr,
         'default DNS servers' :             dns_servers.split(' '),

meson_options.txt

@@ -353,6 +353,10 @@ option('default-dns-over-tls', type : 'combo',
        description : 'default DNS-over-TLS mode',
        choices : ['yes', 'opportunistic', 'no'],
        value : 'no')
+option('default-dns-over-https', type : 'combo',
+       description : 'default DNS-over-HTTPS mode',
+       choices : ['yes', 'no'],
+       value : 'no')
 option('default-mdns', type : 'combo',
        choices : ['yes', 'resolve', 'no'],
        description : 'default MulticastDNS mode',
@@ -363,6 +367,8 @@ option('default-llmnr', type : 'combo',
        value : 'yes')
 option('dns-over-tls', type : 'combo', choices : ['auto', 'gnutls', 'openssl', 'true', 'false'],
        description : 'DNS-over-TLS support')
+option('dns-over-https', type : 'combo', choices : ['true', 'false'],
+       description : 'DNS-over-HTTPS support')
 option('dns-servers', type : 'string',
        description : 'space-separated list of default DNS servers',
        value : '1.1.1.1#cloudflare-dns.com 8.8.8.8#dns.google 1.0.0.1#cloudflare-dns.com 8.8.4.4#dns.google 2606:4700:4700::1111#cloudflare-dns.com 2001:4860:4860::8888#dns.google 2606:4700:4700::1001#cloudflare-dns.com 2001:4860:4860::8844#dns.google')

src/import/meson.build

@@ -14,7 +14,6 @@ systemd_pull_sources = files(
         'pull-tar.c',
         'pull-job.c',
         'pull-common.c',
-        'curl-util.c',
 )
 
 systemd_import_sources = files(

src/resolve/meson.build

@@ -117,6 +117,10 @@ if conf.get('ENABLE_DNS_OVER_TLS') == 1
         endif
 endif
 
+if conf.get('ENABLE_DNS_OVER_HTTPS') == 1
+        systemd_resolved_dependencies += libcurl
+endif
+
 link_with = [
         libshared,
         libsystemd_resolve_core,

src/resolve/resolved-dns-server.c

@@ -422,10 +422,17 @@ DnsServerFeatureLevel dns_server_possible_feature_level(DnsServer *s) {
 
         /* Determine the best feature level we care about. If DNSSEC mode is off there's no point in using anything
          * better than EDNS0, hence don't even try. */
-        if (dns_server_get_dnssec_mode(s) != DNSSEC_NO)
+        if (dns_server_get_dnssec_mode(s) != DNSSEC_NO) {
                 best = dns_server_get_dns_over_tls_mode(s) == DNS_OVER_TLS_NO ?
                         DNS_SERVER_FEATURE_LEVEL_DO :
                         DNS_SERVER_FEATURE_LEVEL_TLS_DO;
+                /* TODO: Add HTTPS_PLAIN_DO too? */
+#if ENABLE_DNS_OVER_HTTPS
+                best = dns_server_get_dns_over_https_mode(s) == DNS_OVER_HTTPS_NO ?
+                        DNS_SERVER_FEATURE_LEVEL_DO :
+                        DNS_SERVER_FEATURE_LEVEL_HTTPS_PLAIN;
+#endif
+        }
         else
                 best = dns_server_get_dns_over_tls_mode(s) == DNS_OVER_TLS_NO ?
                         DNS_SERVER_FEATURE_LEVEL_EDNS0 :
@@ -493,7 +500,8 @@ DnsServerFeatureLevel dns_server_possible_feature_level(DnsServer *s) {
                 } else if (s->packet_bad_opt &&
                            DNS_SERVER_FEATURE_LEVEL_IS_EDNS0(s->possible_feature_level) &&
                            dns_server_get_dnssec_mode(s) != DNSSEC_YES &&
-                           dns_server_get_dns_over_tls_mode(s) != DNS_OVER_TLS_YES) {
+                           dns_server_get_dns_over_tls_mode(s) != DNS_OVER_TLS_YES &&
+                           dns_server_get_dns_over_https_mode(s) != DNS_OVER_HTTPS_YES) {
 
                         /* A reply to one of our EDNS0 queries didn't carry a valid OPT RR, then downgrade to
                          * below EDNS0 levels. After all, some servers generate different responses with and
@@ -962,6 +970,12 @@ DnsOverTlsMode dns_server_get_dns_over_tls_mode(DnsServer *s) {
         return manager_get_dns_over_tls_mode(s->manager);
 }
 
+DnsOverHttpsMode dns_server_get_dns_over_https_mode(DnsServer *s) {
+        assert(s);
+
+        return manager_get_dns_over_https_mode(s->manager);
+}
+
 void dns_server_flush_cache(DnsServer *s) {
         DnsServer *current;
         DnsScope *scope;
@@ -1099,6 +1113,7 @@ static const char* const dns_server_feature_level_table[_DNS_SERVER_FEATURE_LEVE
         [DNS_SERVER_FEATURE_LEVEL_UDP]         = "UDP",
         [DNS_SERVER_FEATURE_LEVEL_EDNS0]       = "UDP+EDNS0",
         [DNS_SERVER_FEATURE_LEVEL_TLS_PLAIN]   = "TLS+EDNS0",
+        [DNS_SERVER_FEATURE_LEVEL_HTTPS_PLAIN] = "HTTPS+EDNS0",
         [DNS_SERVER_FEATURE_LEVEL_DO]          = "UDP+EDNS0+DO",
         [DNS_SERVER_FEATURE_LEVEL_TLS_DO]      = "TLS+EDNS0+DO",
 };

src/resolve/resolved-dns-server.h

@@ -35,6 +35,7 @@ typedef enum DnsServerFeatureLevel {
         DNS_SERVER_FEATURE_LEVEL_UDP,
         DNS_SERVER_FEATURE_LEVEL_EDNS0,
         DNS_SERVER_FEATURE_LEVEL_TLS_PLAIN,
+        DNS_SERVER_FEATURE_LEVEL_HTTPS_PLAIN,
         DNS_SERVER_FEATURE_LEVEL_DO,
         DNS_SERVER_FEATURE_LEVEL_TLS_DO,
         _DNS_SERVER_FEATURE_LEVEL_MAX,
@@ -46,6 +47,7 @@ typedef enum DnsServerFeatureLevel {
 #define DNS_SERVER_FEATURE_LEVEL_IS_EDNS0(x) ((x) >= DNS_SERVER_FEATURE_LEVEL_EDNS0)
 #define DNS_SERVER_FEATURE_LEVEL_IS_TLS(x) IN_SET(x, DNS_SERVER_FEATURE_LEVEL_TLS_PLAIN, DNS_SERVER_FEATURE_LEVEL_TLS_DO)
 #define DNS_SERVER_FEATURE_LEVEL_IS_DNSSEC(x) ((x) >= DNS_SERVER_FEATURE_LEVEL_DO)
+#define DNS_SERVER_FEATURE_LEVEL_IS_HTTPS(x) ((x) == DNS_SERVER_FEATURE_LEVEL_HTTPS_PLAIN)
 #define DNS_SERVER_FEATURE_LEVEL_IS_UDP(x) IN_SET(x, DNS_SERVER_FEATURE_LEVEL_UDP, DNS_SERVER_FEATURE_LEVEL_EDNS0, DNS_SERVER_FEATURE_LEVEL_DO)
 
 const char* dns_server_feature_level_to_string(DnsServerFeatureLevel i) _const_;
@@ -164,6 +166,7 @@ void manager_next_dns_server(Manager *m, DnsServer *if_current);
 
 DnssecMode dns_server_get_dnssec_mode(DnsServer *s);
 DnsOverTlsMode dns_server_get_dns_over_tls_mode(DnsServer *s);
+DnsOverHttpsMode dns_server_get_dns_over_https_mode(DnsServer *s);
 
 size_t dns_server_get_mtu(DnsServer *s);
 

src/resolve/resolved-dns-transaction.c

@@ -4,11 +4,13 @@
 
 #include "af-list.h"
 #include "alloc-util.h"
+
 #include "dns-domain.h"
 #include "errno-list.h"
 #include "errno-util.h"
 #include "fd-util.h"
 #include "glyph-util.h"
+#include "hexdecoct.h"
 #include "random-util.h"
 #include "resolved-dns-cache.h"
 #include "resolved-dns-transaction.h"
@@ -16,6 +18,10 @@
 #include "resolved-llmnr.h"
 #include "string-table.h"
 
+#if ENABLE_DNS_OVER_HTTPS
+#include "curl-util.h"
+#endif
+
 #define TRANSACTIONS_MAX 4096
 #define TRANSACTION_TCP_TIMEOUT_USEC (10U*USEC_PER_SEC)
 
@@ -682,7 +688,13 @@ static uint16_t dns_transaction_port(DnsTransaction *t) {
         if (t->server->port > 0)
                 return t->server->port;
 
-        return DNS_SERVER_FEATURE_LEVEL_IS_TLS(t->current_feature_level) ? 853 : 53;
+        if (DNS_SERVER_FEATURE_LEVEL_IS_TLS(t->current_feature_level))
+                return 853;
+
+        if (DNS_SERVER_FEATURE_LEVEL_IS_HTTPS(t->current_feature_level))
+                return 443;
+
+        return 53;
 }
 
 static int dns_transaction_emit_tcp(DnsTransaction *t) {
@@ -1518,6 +1530,9 @@ static int dns_transaction_emit_udp(DnsTransaction *t) {
                 if (t->current_feature_level < DNS_SERVER_FEATURE_LEVEL_UDP || DNS_SERVER_FEATURE_LEVEL_IS_TLS(t->current_feature_level))
                         return -EAGAIN; /* Sorry, can't do UDP, try TCP! */
 
+                if (DNS_SERVER_FEATURE_LEVEL_IS_HTTPS(t->current_feature_level))
+                        return -EAGAIN; /* Direct request logic to HTTPS */
+
                 if (!t->bypass && !dns_server_dnssec_supported(t->server) && dns_type_is_dnssec(dns_transaction_key(t)->type))
                         return -EOPNOTSUPP;
 
@@ -1984,6 +1999,223 @@ static int mdns_make_dummy_packet(DnsTransaction *t, DnsPacket **ret_packet, Set
         return add_known_answers;
 }
 
+#if ENABLE_DNS_OVER_HTTPS
+static size_t dns_transaction_curl_header_callback(void *contents, size_t size, size_t nmemb, void *userdata) {
+        _cleanup_free_ char *content_header = NULL;
+        DnsTransaction *t = ASSERT_PTR(userdata);
+        size_t sz = size * nmemb;
+        CURLcode code;
+        long status;
+        int r;
+
+        assert(contents);
+
+        code = curl_easy_getinfo(t->curl, CURLINFO_RESPONSE_CODE, &status);
+        if (code != CURLE_OK)
+                return log_error_errno(SYNTHETIC_ERRNO(EIO), "Failed to retrieve response code: %s", curl_easy_strerror(code));
+
+        if (status >= 200 && status <= 299) {
+                r = curl_header_strdup(contents, sz, "Content-Type:", &content_header);
+                if (r < 0) {
+                        log_oom();
+                        return 0;
+                }
+                if (r > 0) {
+                        r = strcmp("application/dns-message", content_header);
+                        if (r == 0)
+                                t->valid_dns_message = true;
+                        return sz;
+                }
+        }
+
+        return sz;
+}
+
+static size_t dns_transaction_curl_write_callback(void *contents, size_t size, size_t nmemb, void *userdata) {
+        DnsTransaction *t = ASSERT_PTR(userdata);
+        size_t sz = size * nmemb;
+        int r;
+
+        t->payload = memdup(contents, sz);
+        if (!t->payload) {
+                log_debug("Failed to extract HTTP payload to further processing");
+                r = log_oom();
+                goto fail;
+        }
+
+        t->payload_size += sz;
+
+        return sz;
+
+ fail:
+        dns_transaction_complete(t, DNS_TRANSACTION_INVALID_REPLY);
+        return r;
+}
+
+static int dns_transaction_curl_recv(DnsTransaction *t, DnsPacket **p) {
+        size_t ms;
+        int r;
+
+        ms = t->payload_size;
+
+        if (t->payload_size < 1) {
+                log_debug("Received HTTP payload unexpected size %zu", t->payload_size);
+                return -1;
+        }
+
+        r = dns_packet_new(p, DNS_PROTOCOL_DNS, ms, DNS_PACKET_SIZE_MAX);
+        if (r < 0)
+                return r;
+
+        log_debug("Received HTTP payload of size %zu", t->payload_size);
+        return 0;
+}
+
+static int dns_transaction_curl_make_url(DnsTransaction *t, char **url) {
+        _cleanup_free_ char *base64_string = NULL;
+        uint8_t *packet_to_send = DNS_PACKET_DATA(t->sent);
+        int r;
+
+        /* Let's zero the query ID according to the RFC */
+        packet_to_send[0] = 0;
+        packet_to_send[1] = 0;
+
+        r = base64mem_full(packet_to_send, t->sent->size, MAX_URL_LENGTH, &base64_string);
+        if (r < 0) {
+                log_debug_errno(r, "Failed to encode DNS packet to base64");
+                return r;
+        }
+
+        /* Remove base64 trailing characters */
+        delete_trailing_chars(base64_string, "=");
+
+        /* Build the DoH's wire format request URL */
+        r = asprintf(url, "https://%s/dns-query?dns=%s", t->server->server_string, base64_string);
+        if (r < 0) {
+                log_debug("Failed to allocate and set the url for transaction %" PRIu16 ".", t->id);
+                return r;
+        }
+
+        return 0;
+}
+
+static void dns_transaction_curl_on_response(CurlGlue *g, CURL *curl, CURLcode result) {
+        _cleanup_(dns_packet_unrefp) DnsPacket *p = NULL;
+        DnsTransaction *t = NULL;
+        int status;
+        int r;
+
+        assert(g);
+        assert(curl);
+
+        curl_easy_getinfo(curl, CURLINFO_PRIVATE, &t);
+
+        if (result != CURLE_OK) {
+                log_error_errno(SYNTHETIC_ERRNO(EIO), "HTTP request failed: %s", curl_easy_strerror(result));
+                status = DNS_TRANSACTION_INVALID_REPLY;
+                goto finish;
+        }
+
+        if (!t->valid_dns_message) {
+                log_debug("Received invalid HTTP payload, expected content type of application/dns-message");
+                status = DNS_TRANSACTION_INVALID_REPLY;
+                goto finish;
+        }
+
+        r = dns_transaction_curl_recv(t, &p);
+        if (r < 0) {
+                log_debug_errno(r, "HTTP payload receive failure");
+                dns_transaction_complete_errno(t, r);
+                return;
+        }
+
+        /* Transfer the received payload to transaction/packet struct */
+        uint8_t *p_data = DNS_PACKET_DATA(p);
+        memcpy(p_data, t->payload, t->payload_size);
+
+        p->size = t->payload_size;
+
+        r = dns_packet_validate_reply(p);
+        if (r < 0)
+                log_debug_errno(r, "Received invalid DNS packet as response, ignoring: %m");
+
+        if (r == 0)
+                log_debug("Received inappropriate DNS packet as response, ignoring");
+
+        dns_transaction_process_reply(t, p, false);
+
+        return;
+ finish:
+        dns_transaction_complete(t, status);
+}
+
+static int dns_transaction_emit_curl(DnsTransaction *t) {
+        _cleanup_(sd_event_unrefp) sd_event *e = NULL;
+        _cleanup_free_ char *rule = NULL;
+        int r;
+
+        assert(t);
+        assert(t->sent);
+
+        dns_transaction_close_connection(t, true);
+
+        if (t->scope->protocol == DNS_PROTOCOL_DNS) {
+                r = dns_transaction_pick_server(t);
+                if (r < 0)
+                        return r;
+
+                if (manager_server_is_stub(t->scope->manager, t->server))
+                        return -ELOOP;
+
+                r = curl_glue_new(&t->glue, e);
+                if (r < 0)
+                        return r;
+
+                t->glue->on_finished = dns_transaction_curl_on_response;
+
+                r = dns_transaction_curl_make_url(t, &t->url);
+                if (r < 0)
+                        return r;
+
+                r = curl_glue_make(&t->curl, t->url, t);
+                if (r < 0)
+                        return r;
+
+                if (curl_easy_setopt(t->curl, CURLOPT_HEADERFUNCTION, dns_transaction_curl_header_callback) != CURLE_OK)
+                        return -EIO;
+
+                if (curl_easy_setopt(t->curl, CURLOPT_HEADERDATA, t) != CURLE_OK)
+                        return -EIO;
+
+                if (curl_easy_setopt(t->curl, CURLOPT_WRITEFUNCTION, dns_transaction_curl_write_callback) != CURLE_OK)
+                        return -EIO;
+
+                if (curl_easy_setopt(t->curl, CURLOPT_WRITEDATA, t) != CURLE_OK)
+                        return -EIO;
+
+                // Prevents libcurl's native name lookups
+                r = asprintf(&rule, "%s:443:%s", t->server->server_string, t->server->server_string);
+                if (r < 0) {
+                        log_debug("Failed to compound IP resolution to CURLOPT_RESOLVE parameter");
+                        return r;
+                }
+
+                t->glue->resolve_rules = curl_slist_append(NULL, rule);
+                if (curl_easy_setopt(t->curl, CURLOPT_RESOLVE, t->glue->resolve_rules) != CURLE_OK)
+                        return -EIO;
+
+
+                log_debug("Emitting HTTPS request via curl for transaction %" PRIu16, t->id);
+                r = curl_glue_add(t->glue, t->curl);
+                if (r < 0)
+                        return r;
+        } else
+                /* TODO: Is this the right error code here? */
+                return -ELOOP;
+
+        return 0;
+}
+#endif
 static int dns_transaction_make_packet_mdns(DnsTransaction *t) {
         _cleanup_(dns_packet_unrefp) DnsPacket *p = NULL, *dummy = NULL;
         _cleanup_set_free_ Set *keys = NULL;
@@ -2172,10 +2404,20 @@ int dns_transaction_go(DnsTransaction *t) {
                 r = dns_transaction_emit_udp(t);
                 if (r == -EMSGSIZE)
                         log_debug("Sending query via TCP since it is too large.");
+#if ENABLE_DNS_OVER_HTTPS
+                else if ((r == -EAGAIN &&
+                          (DNS_SERVER_FEATURE_LEVEL_IS_HTTPS(t->current_feature_level))))
+                        log_debug("Sending query via HTTPS.");
+#endif
                 else if (r == -EAGAIN)
                         log_debug("Sending query via TCP since UDP isn't supported or DNS-over-TLS is selected.");
                 else if (r == -EPERM)
                         log_debug("Sending query via TCP since UDP is blocked.");
+#if ENABLE_DNS_OVER_HTTPS
+                if ((r == -EAGAIN &&
+                          (DNS_SERVER_FEATURE_LEVEL_IS_HTTPS(t->current_feature_level))))
+                        r = dns_transaction_emit_curl(t);
+#endif
                 if (IN_SET(r, -EMSGSIZE, -EAGAIN, -EPERM))
                         r = dns_transaction_emit_tcp(t);
         }

src/resolve/resolved-dns-transaction.h

@@ -1,9 +1,19 @@
 /* SPDX-License-Identifier: LGPL-2.1-or-later */
 #pragma once
 
+#if ENABLE_DNS_OVER_HTTPS
+#include <curl/curl.h>
+#endif
+
 #include "sd-event.h"
+
+#if ENABLE_DNS_OVER_HTTPS
+#include "curl-util.h"
+#endif
+
 #include "in-addr-util.h"
 
+
 typedef struct DnsTransaction DnsTransaction;
 typedef struct DnsTransactionFinder DnsTransactionFinder;
 typedef enum DnsTransactionState DnsTransactionState;
@@ -92,7 +102,15 @@ struct DnsTransaction {
 
         /* TCP connection logic, if we need it */
         DnsStream *stream;
-
+#if ENABLE_DNS_OVER_HTTPS
+        /* HTTPS connection logic, if we need it */
+        CurlGlue *glue;
+        CURL *curl;
+        char *url;
+        uint8_t *payload;
+        size_t payload_size;
+        bool valid_dns_message;
+#endif
         /* The active server */
         DnsServer *server;
 
@@ -219,6 +237,9 @@ DnsTransactionSource dns_transaction_source_from_string(const char *s) _pure_;
 /* Maximum attempts to send MDNS requests, see RFC 6762 Section 8.1 */
 #define MDNS_TRANSACTION_ATTEMPTS_MAX 3
 
+/* Maximum URL length for HTTP GET request, see RFC ... */
+#define MAX_URL_LENGTH 2048
+
 #define TRANSACTION_ATTEMPTS_MAX(p) ((p) == DNS_PROTOCOL_LLMNR ?        \
                                      LLMNR_TRANSACTION_ATTEMPTS_MAX :   \
                                      (p) == DNS_PROTOCOL_MDNS ?         \

src/resolve/resolved-gperf.gperf

@@ -26,6 +26,7 @@ Resolve.LLMNR,                     config_parse_resolve_support,         0,
 Resolve.MulticastDNS,              config_parse_resolve_support,         0,                   offsetof(Manager, mdns_support)
 Resolve.DNSSEC,                    config_parse_dnssec_mode,             0,                   offsetof(Manager, dnssec_mode)
 Resolve.DNSOverTLS,                config_parse_dns_over_tls_mode,       0,                   offsetof(Manager, dns_over_tls_mode)
+Resolve.DNSOverHTTPS,              config_parse_dns_over_https_mode,     0,                   offsetof(Manager, dns_over_https_mode)
 Resolve.Cache,                     config_parse_dns_cache_mode,          DNS_CACHE_MODE_YES,  offsetof(Manager, enable_cache)
 Resolve.DNSStubListener,           config_parse_dns_stub_listener_mode,  0,                   offsetof(Manager, dns_stub_listener_mode)
 Resolve.ReadEtcHosts,              config_parse_bool,                    0,                   offsetof(Manager, read_etc_hosts)

src/resolve/resolved-manager.c

@@ -1670,6 +1670,15 @@ DnsOverTlsMode manager_get_dns_over_tls_mode(Manager *m) {
         return DNS_OVER_TLS_NO;
 }
 
+DnsOverHttpsMode manager_get_dns_over_https_mode(Manager *m) {
+        assert(m);
+
+        if (m->dns_over_https_mode != _DNS_OVER_HTTPS_MODE_INVALID)
+                return m->dns_over_https_mode;
+
+        return DNS_OVER_HTTPS_NO;
+}
+
 void manager_dnssec_verdict(Manager *m, DnssecVerdict verdict, const DnsResourceKey *key) {
 
         assert(verdict >= 0);

src/resolve/resolved-manager.h

@@ -40,6 +40,7 @@ struct Manager {
         ResolveSupport mdns_support;
         DnssecMode dnssec_mode;
         DnsOverTlsMode dns_over_tls_mode;
+        DnsOverHttpsMode dns_over_https_mode;
         DnsCacheMode enable_cache;
         bool cache_from_localhost;
         DnsStubListenerMode dns_stub_listener_mode;
@@ -207,6 +208,8 @@ bool manager_dnssec_supported(Manager *m);
 
 DnsOverTlsMode manager_get_dns_over_tls_mode(Manager *m);
 
+DnsOverHttpsMode manager_get_dns_over_https_mode(Manager *m);
+
 void manager_dnssec_verdict(Manager *m, DnssecVerdict verdict, const DnsResourceKey *key);
 
 bool manager_routable(Manager *m);

src/resolve/resolved.conf.in

@@ -26,6 +26,7 @@
 #Domains=
 #DNSSEC={{DEFAULT_DNSSEC_MODE_STR}}
 #DNSOverTLS={{DEFAULT_DNS_OVER_TLS_MODE_STR}}
+#DNSOverHTTPS={{DEFAULT_DNS_OVER_HTTPS_MODE_STR}}
 #MulticastDNS={{DEFAULT_MDNS_MODE_STR}}
 #LLMNR={{DEFAULT_LLMNR_MODE_STR}}
 #Cache=yes

src/shared/curl-util.c

@@ -311,6 +311,9 @@ void curl_glue_remove_and_free(CurlGlue *g, CURL *c) {
         if (g->curl)
                 curl_multi_remove_handle(g->curl, c);
 
+        if (g->resolve_rules)
+                curl_slist_free_all(g->resolve_rules);
+
         curl_easy_cleanup(c);
 }
 

src/shared/curl-util.h

@@ -20,6 +20,7 @@ struct CurlGlue {
 
         void (*on_finished)(CurlGlue *g, CURL *curl, CURLcode code);
         void *userdata;
+        struct curl_slist *resolve_rules;;
 };
 
 int curl_glue_new(CurlGlue **glue, sd_event *event);

src/shared/meson.build

@@ -256,6 +256,10 @@ if conf.get('HAVE_TPM2') == 1 and conf.get('HAVE_LIBCRYPTSETUP') == 1
         shared_sources += files('cryptsetup-tpm2.c')
 endif
 
+if conf.get('HAVE_LIBCURL') == 1
+        shared_sources += files('curl-util.c')
+endif
+
 generate_ip_protocol_list = find_program('generate-ip-protocol-list.sh')
 ip_protocol_list_txt = custom_target(
         'ip-protocol-list.txt',
@@ -337,6 +341,11 @@ libshared_deps = [threads,
                   libxz_cflags,
                   libzstd_cflags]
 
+# Is this correct?
+if conf.get('HAVE_LIBCURL') == 1
+        libshared_deps += [libcurl]
+endif
+
 libshared_sym_path = meson.current_source_dir() / 'libshared.sym'
 libshared_build_dir = meson.current_build_dir()
 

src/shared/resolve-util.c

@@ -7,6 +7,7 @@
 DEFINE_CONFIG_PARSE_ENUM(config_parse_resolve_support, resolve_support, ResolveSupport);
 DEFINE_CONFIG_PARSE_ENUM(config_parse_dnssec_mode, dnssec_mode, DnssecMode);
 DEFINE_CONFIG_PARSE_ENUM(config_parse_dns_over_tls_mode, dns_over_tls_mode, DnsOverTlsMode);
+DEFINE_CONFIG_PARSE_ENUM(config_parse_dns_over_https_mode, dns_over_https_mode, DnsOverHttpsMode);
 
 static const char* const resolve_support_table[_RESOLVE_SUPPORT_MAX] = {
         [RESOLVE_SUPPORT_NO] = "no",
@@ -29,6 +30,12 @@ static const char* const dns_over_tls_mode_table[_DNS_OVER_TLS_MODE_MAX] = {
 };
 DEFINE_STRING_TABLE_LOOKUP_WITH_BOOLEAN(dns_over_tls_mode, DnsOverTlsMode, DNS_OVER_TLS_YES);
 
+static const char* const dns_over_https_mode_table[_DNS_OVER_HTTPS_MODE_MAX] = {
+        [DNS_OVER_HTTPS_NO] = "no",
+        [DNS_OVER_HTTPS_YES] = "yes",
+};
+DEFINE_STRING_TABLE_LOOKUP_WITH_BOOLEAN(dns_over_https_mode, DnsOverHttpsMode, DNS_OVER_HTTPS_YES);
+
 bool dns_server_address_valid(int family, const union in_addr_union *sa) {
 
         /* Refuses the 0 IP addresses as well as 127.0.0.53/127.0.0.54 (which is our own DNS stub) */

src/shared/resolve-util.h

@@ -27,6 +27,7 @@ enum DnsCacheMode {
 typedef enum ResolveSupport ResolveSupport;
 typedef enum DnssecMode DnssecMode;
 typedef enum DnsOverTlsMode DnsOverTlsMode;
+typedef enum DnsOverHttpsMode DnsOverHttpsMode;
 
 /* Do not change the order, see link_get_llmnr_support() or link_get_mdns_support(). */
 enum ResolveSupport {
@@ -70,9 +71,21 @@ enum DnsOverTlsMode {
         _DNS_OVER_TLS_MODE_INVALID = -EINVAL,
 };
 
+enum DnsOverHttpsMode {
+        /* No connection is made for DNS-over-HTTPS */
+        DNS_OVER_HTTPS_NO,
+
+        /* Enforce DNS-over-HTTPS */
+        DNS_OVER_HTTPS_YES,
+
+        _DNS_OVER_HTTPS_MODE_MAX,
+        _DNS_OVER_HTTPS_MODE_INVALID = -EINVAL,
+};
+
 CONFIG_PARSER_PROTOTYPE(config_parse_resolve_support);
 CONFIG_PARSER_PROTOTYPE(config_parse_dnssec_mode);
 CONFIG_PARSER_PROTOTYPE(config_parse_dns_over_tls_mode);
+CONFIG_PARSER_PROTOTYPE(config_parse_dns_over_https_mode);
 CONFIG_PARSER_PROTOTYPE(config_parse_dns_cache_mode);
 
 const char* resolve_support_to_string(ResolveSupport p) _const_;
@@ -84,6 +97,9 @@ DnssecMode dnssec_mode_from_string(const char *s) _pure_;
 const char* dns_over_tls_mode_to_string(DnsOverTlsMode p) _const_;
 DnsOverTlsMode dns_over_tls_mode_from_string(const char *s) _pure_;
 
+const char* dns_over_https_mode_to_string(DnsOverHttpsMode p) _const_;
+DnsOverHttpsMode dns_over_https_mode_from_string(const char *s) _pure_;
+
 bool dns_server_address_valid(int family, const union in_addr_union *sa);
 
 const char* dns_cache_mode_to_string(DnsCacheMode p) _const_;