resolved: properly implement RRSIG validation of wildcarded RRsets

Note that this is still not complete, one additional step is still
missing: when we verified that a wildcard RRset is properly signed, we
still need to do an NSEC/NSEC3 proof that no more specific RRset exists.

src/resolve/resolved-dns-dnssec.c

@@ -384,10 +384,17 @@ int dnssec_verify_rrset(
         gcry_md_write(md, wire_format_name, r);
 
         for (k = 0; k < n; k++) {
+                const char *suffix;
                 size_t l;
                 rr = list[k];
 
-                r = dns_name_to_wire_format(DNS_RESOURCE_KEY_NAME(rr->key), wire_format_name, sizeof(wire_format_name), true);
+                r = dns_name_suffix(DNS_RESOURCE_KEY_NAME(rr->key), rrsig->rrsig.labels, &suffix);
+                if (r < 0)
+                        goto finish;
+                if (r > 0) /* This is a wildcard! */
+                        gcry_md_write(md, (uint8_t[]) { 1, '*'}, 2);
+
+                r = dns_name_to_wire_format(suffix, wire_format_name, sizeof(wire_format_name), true);
                 if (r < 0)
                         goto finish;
                 gcry_md_write(md, wire_format_name, r);
@@ -497,6 +504,8 @@ int dnssec_rrsig_match_dnskey(DnsResourceRecord *rrsig, DnsResourceRecord *dnske
 }
 
 int dnssec_key_match_rrsig(const DnsResourceKey *key, DnsResourceRecord *rrsig) {
+        int r;
+
         assert(key);
         assert(rrsig);
 
@@ -509,6 +518,18 @@ int dnssec_key_match_rrsig(const DnsResourceKey *key, DnsResourceRecord *rrsig)
         if (rrsig->rrsig.type_covered != key->type)
                 return 0;
 
+        /* Make sure signer is a parent of the RRset */
+        r = dns_name_endswith(DNS_RESOURCE_KEY_NAME(rrsig->key), rrsig->rrsig.signer);
+        if (r <= 0)
+                return r;
+
+        /* Make sure the owner name has at least as many labels as the "label" fields indicates. */
+        r = dns_name_count_labels(DNS_RESOURCE_KEY_NAME(rrsig->key));
+        if (r < 0)
+                return r;
+        if (r < rrsig->rrsig.labels)
+                return 0;
+
         return dns_name_equal(DNS_RESOURCE_KEY_NAME(rrsig->key), DNS_RESOURCE_KEY_NAME(key));
 }
 

src/shared/dns-domain.c

@@ -1159,3 +1159,59 @@ finish:
 
         return 0;
 }
+
+int dns_name_suffix(const char *name, unsigned n_labels, const char **ret) {
+        const char* labels[DNS_N_LABELS_MAX+1];
+        unsigned n = 0;
+        const char *p;
+        int r;
+
+        assert(name);
+        assert(ret);
+
+        p = name;
+        for (;;) {
+                if (n > DNS_N_LABELS_MAX)
+                        return -EINVAL;
+
+                labels[n] = p;
+
+                r = dns_name_parent(&p);
+                if (r < 0)
+                        return r;
+                if (r == 0)
+                        break;
+
+                n++;
+        }
+
+        if (n < n_labels)
+                return -EINVAL;
+
+        *ret = labels[n - n_labels];
+        return (int) (n - n_labels);
+}
+
+int dns_name_count_labels(const char *name) {
+        unsigned n = 0;
+        const char *p;
+        int r;
+
+        assert(name);
+
+        p = name;
+        for (;;) {
+                r = dns_name_parent(&p);
+                if (r < 0)
+                        return r;
+                if (r == 0)
+                        break;
+
+                if (n >= DNS_N_LABELS_MAX)
+                        return -EINVAL;
+
+                n++;
+        }
+
+        return (int) n;
+}

src/shared/dns-domain.h

@@ -42,6 +42,9 @@
 /* Maximum length of a full hostname, on the wire, including the final NUL byte */
 #define DNS_WIRE_FOMAT_HOSTNAME_MAX 255
 
+/* Maximum number of labels per valid hostname */
+#define DNS_N_LABELS_MAX 127
+
 int dns_label_unescape(const char **name, char *dest, size_t sz);
 int dns_label_unescape_suffix(const char *name, const char **label_end, char *dest, size_t sz);
 int dns_label_escape(const char *p, size_t l, char *dest, size_t sz);
@@ -96,3 +99,6 @@ bool dns_service_name_is_valid(const char *name);
 
 int dns_service_join(const char *name, const char *type, const char *domain, char **ret);
 int dns_service_split(const char *joined, char **name, char **type, char **domain);
+
+int dns_name_suffix(const char *name, unsigned n_labels, const char **ret);
+int dns_name_count_labels(const char *name);

src/test/test-dns-domain.c

@@ -475,6 +475,46 @@ static void test_dns_name_change_suffix(void) {
         test_dns_name_change_suffix_one("a", "b", "c", 0, NULL);
 }
 
+static void test_dns_name_suffix_one(const char *name, unsigned n_labels, const char *result, int ret) {
+        const char *p = NULL;
+
+        assert_se(ret == dns_name_suffix(name, n_labels, &p));
+        assert_se(streq_ptr(p, result));
+}
+
+static void test_dns_name_suffix(void) {
+        test_dns_name_suffix_one("foo.bar", 2, "foo.bar", 0);
+        test_dns_name_suffix_one("foo.bar", 1, "bar", 1);
+        test_dns_name_suffix_one("foo.bar", 0, "", 2);
+        test_dns_name_suffix_one("foo.bar", 3, NULL, -EINVAL);
+        test_dns_name_suffix_one("foo.bar", 4, NULL, -EINVAL);
+
+        test_dns_name_suffix_one("bar", 1, "bar", 0);
+        test_dns_name_suffix_one("bar", 0, "", 1);
+        test_dns_name_suffix_one("bar", 2, NULL, -EINVAL);
+        test_dns_name_suffix_one("bar", 3, NULL, -EINVAL);
+
+        test_dns_name_suffix_one("", 0, "", 0);
+        test_dns_name_suffix_one("", 1, NULL, -EINVAL);
+        test_dns_name_suffix_one("", 2, NULL, -EINVAL);
+}
+
+static void test_dns_name_count_labels_one(const char *name, int n) {
+        assert_se(dns_name_count_labels(name) == n);
+}
+
+static void test_dns_name_count_labels(void) {
+        test_dns_name_count_labels_one("foo.bar.quux.", 3);
+        test_dns_name_count_labels_one("foo.bar.quux", 3);
+        test_dns_name_count_labels_one("foo.bar.", 2);
+        test_dns_name_count_labels_one("foo.bar", 2);
+        test_dns_name_count_labels_one("foo.", 1);
+        test_dns_name_count_labels_one("foo", 1);
+        test_dns_name_count_labels_one("", 0);
+        test_dns_name_count_labels_one(".", 0);
+        test_dns_name_count_labels_one("..", -EINVAL);
+}
+
 int main(int argc, char *argv[]) {
 
         test_dns_label_unescape();
@@ -495,6 +535,8 @@ int main(int argc, char *argv[]) {
         test_dns_service_join();
         test_dns_service_split();
         test_dns_name_change_suffix();
+        test_dns_name_suffix();
+        test_dns_name_count_labels();
 
         return 0;
 }