resolved: NSEC3 hash algorithms are distinct from DS digest algorithms

Previously, we'd use the same set of identifiers for both, but that's
actually incorrect. It didn't matter much since the only NSEC3 hash
algorithm defined (SHA-1) is mapped to code 1 which is also what it is
encoded as in DS digests, but we really should make sure to use two
distinct enumerations.

Author: poettering

src/resolve/resolved-dns-dnssec.c

@@ -1057,6 +1057,20 @@ int dnssec_verify_dnskey_search(DnsResourceRecord *dnskey, DnsAnswer *validated_
         return 0;
 }
 
+static int nsec3_hash_to_gcrypt_md(uint8_t algorithm) {
+
+        /* Translates a DNSSEC NSEC3 hash algorithm into a gcrypt digest identifier */
+
+        switch (algorithm) {
+
+        case NSEC3_ALGORITHM_SHA1:
+                return GCRY_MD_SHA1;
+
+        default:
+                return -EOPNOTSUPP;
+        }
+}
+
 int dnssec_nsec3_hash(DnsResourceRecord *nsec3, const char *name, void *ret) {
         uint8_t wire_format[DNS_WIRE_FOMAT_HOSTNAME_MAX];
         gcry_md_hd_t md = NULL;
@@ -1073,7 +1087,7 @@ int dnssec_nsec3_hash(DnsResourceRecord *nsec3, const char *name, void *ret) {
         if (nsec3->key->type != DNS_TYPE_NSEC3)
                 return -EINVAL;
 
-        algorithm = digest_to_gcrypt_md(nsec3->nsec3.algorithm);
+        algorithm = nsec3_hash_to_gcrypt_md(nsec3->nsec3.algorithm);
         if (algorithm < 0)
                 return algorithm;
 
@@ -1138,6 +1152,10 @@ static int nsec3_is_good(DnsResourceRecord *rr, DnsAnswerFlags flags, DnsResourc
         if (!IN_SET(rr->nsec3.flags, 0, 1))
                 return 0;
 
+        /* Ignore NSEC3 RRs whose algorithm we don't know */
+        if (nsec3_hash_to_gcrypt_md(rr->nsec3.algorithm) < 0)
+                return 0;
+
         if (!nsec3)
                 return 1;
 

src/resolve/resolved-dns-rr.h

@@ -72,6 +72,13 @@ enum {
         _DNSSEC_DIGEST_MAX_DEFINED
 };
 
+/* DNSSEC NSEC3 hash algorithms, see
+ * https://www.iana.org/assignments/dnssec-nsec3-parameters/dnssec-nsec3-parameters.xhtml */
+enum {
+        NSEC3_ALGORITHM_SHA1 = 1,
+        _NSEC3_ALGORITHM_MAX_DEFINED
+};
+
 struct DnsResourceKey {
         unsigned n_ref;
         uint16_t class, type;