diff options
| -rw-r--r-- | src/resolve/resolved-dns-packet.c | 107 |
1 files changed, 88 insertions, 19 deletions
diff --git a/src/resolve/resolved-dns-packet.c b/src/resolve/resolved-dns-packet.c index a8a8632491..57cfc1ab9b 100644 --- a/src/resolve/resolved-dns-packet.c +++ b/src/resolve/resolved-dns-packet.c @@ -2017,6 +2017,48 @@ fail: return r; } +static bool opt_is_good(DnsResourceRecord *rr, bool *rfc6975) { + const uint8_t* p; + bool found_dau_dhu_n3u = false; + size_t l; + + /* Checks whether the specified OPT RR is well-formed and whether it contains RFC6975 data (which is not OK in + * a reply). */ + + assert(rr); + assert(rr->key->type == DNS_TYPE_OPT); + + /* Check that the version is 0 */ + if (((rr->ttl >> 16) & UINT32_C(0xFF)) != 0) + return false; + + p = rr->opt.data; + l = rr->opt.size; + while (l > 0) { + uint16_t option_code, option_length; + + /* At least four bytes for OPTION-CODE and OPTION-LENGTH are required */ + if (l < 4U) + return false; + + option_code = unaligned_read_be16(p); + option_length = unaligned_read_be16(p + 2); + + if (l < option_length + 4U) + return false; + + /* RFC 6975 DAU, DHU or N3U fields found. */ + if (IN_SET(option_code, 5, 6, 7)) + found_dau_dhu_n3u = true; + + p += option_length + 4U; + l -= option_length + 4U; + } + + *rfc6975 = found_dau_dhu_n3u; + return true; +} + int dns_packet_extract(DnsPacket *p) { _cleanup_(dns_question_unrefp) DnsQuestion *question = NULL; _cleanup_(dns_answer_unrefp) DnsAnswer *answer = NULL; @@ -2064,6 +2106,8 @@ int dns_packet_extract(DnsPacket *p) { n = DNS_PACKET_RRCOUNT(p); if (n > 0) { + bool bad_opt = false; + answer = dns_answer_new(n); if (!answer) { r = -ENOMEM; @@ -2079,35 +2123,57 @@ int dns_packet_extract(DnsPacket *p) { goto finish; if (rr->key->type == DNS_TYPE_OPT) { + bool has_rfc6975; + + if (p->opt || bad_opt) { + /* Multiple OPT RRs? if so, let's ignore all, because there's something wrong + * with the server, and if one is valid we wouldn't know which one. */ + log_debug("Multiple OPT RRs detected, ignoring all."); + bad_opt = true; + continue; + } if (!dns_name_is_root(DNS_RESOURCE_KEY_NAME(rr->key))) { - r = -EBADMSG; - goto finish; + /* If the OPT RR qis not owned by the root domain, then it is bad, let's ignore + * it. */ + log_debug("OPT RR is not owned by root domain, ignoring."); + bad_opt = true; + continue; + } + + if (i < DNS_PACKET_ANCOUNT(p) + DNS_PACKET_NSCOUNT(p)) { + /* OPT RR is in the wrong section? Some Belkin routers do this. This is a hint + * the EDNS implementation is borked, like the Belkin one is, hence ignore + * it. */ + log_debug("OPT RR in wrong section, ignoring."); + bad_opt = true; + continue; } - /* Note that we accept the OPT RR in - * any section, not just in the - * additional section, as some routers - * (Belkin!) blindly copy the OPT RR - * from the query to the reply packet, - * and don't get the section right. */ + if (!opt_is_good(rr, &has_rfc6975)) { + log_debug("Malformed OPT RR, ignoring."); + bad_opt = true; + continue; + } - /* Two OPT RRs? */ - if (p->opt) { - r = -EBADMSG; - goto finish; + if (has_rfc6975) { + /* OPT RR contains RFC6975 algorithm data, then this is indication that the + * server just copied the OPT it got from us (which contained that data) back + * into the reply. If so, then it doesn't properly support EDNS, as RFC6975 + * makes it very clear that the algorithm data should only be contained in + * questions, never in replies. Crappy Belkin copy the OPT data for example, + * hence let's detect this so that we downgrade early. */ + log_debug("OPT RR contained RFC6975 data, ignoring."); + bad_opt = true; + continue; } p->opt = dns_resource_record_ref(rr); } else { - /* According to RFC 4795, section - * 2.9. only the RRs from the Answer - * section shall be cached. Hence mark - * only those RRs as cacheable by - * default, but not the ones from the - * Additional or Authority - * sections. */ + /* According to RFC 4795, section 2.9. only the RRs from the Answer section shall be + * cached. Hence mark only those RRs as cacheable by default, but not the ones from the + * Additional or Authority sections. */ r = dns_answer_add(answer, rr, p->ifindex, (i < DNS_PACKET_ANCOUNT(p) ? DNS_ANSWER_CACHEABLE : 0) | @@ -2116,6 +2182,9 @@ int dns_packet_extract(DnsPacket *p) { goto finish; } } + + if (bad_opt) + p->opt = dns_resource_record_unref(p->opt); } p->question = question; |