From 9c4d403ae09fb5a07409467797bec84946352249 Mon Sep 17 00:00:00 2001 From: moneromooo-monero Date: Mon, 25 Feb 2019 22:16:18 +0000 Subject: [PATCH] dns_utils: use fallback if the default resolver does not support DNSSEC --- src/common/dns_utils.cpp | 40 ++++++++++++++++++++++++++++++++++------ 1 file changed, 34 insertions(+), 6 deletions(-) diff --git a/src/common/dns_utils.cpp b/src/common/dns_utils.cpp index 417b5b4ac..d414e73a3 100644 --- a/src/common/dns_utils.cpp +++ b/src/common/dns_utils.cpp @@ -232,13 +232,24 @@ public: char *str; }; +static void add_anchors(ub_ctx *ctx) +{ + const char * const *ds = ::get_builtin_ds(); + while (*ds) + { + MINFO("adding trust anchor: " << *ds); + ub_ctx_add_ta(ctx, string_copy(*ds++)); + } +} + DNSResolver::DNSResolver() : m_data(new DNSResolverData()) { int use_dns_public = 0; std::vector dns_public_addr; - if (auto res = getenv("DNS_PUBLIC")) + const char *DNS_PUBLIC = getenv("DNS_PUBLIC"); + if (DNS_PUBLIC) { - dns_public_addr = tools::dns_utils::parse_dns_public(res); + dns_public_addr = tools::dns_utils::parse_dns_public(DNS_PUBLIC); if (!dns_public_addr.empty()) { MGINFO("Using public DNS server(s): " << boost::join(dns_public_addr, ", ") << " (TCP)"); @@ -266,11 +277,28 @@ DNSResolver::DNSResolver() : m_data(new DNSResolverData()) ub_ctx_hosts(m_data->m_ub_context, NULL); } - const char * const *ds = ::get_builtin_ds(); - while (*ds) + add_anchors(m_data->m_ub_context); + + if (!DNS_PUBLIC) { - MINFO("adding trust anchor: " << *ds); - ub_ctx_add_ta(m_data->m_ub_context, string_copy(*ds++)); + // if no DNS_PUBLIC specified, we try a lookup to what we know + // should be a valid DNSSEC record, and switch to known good + // DNSSEC resolvers if verification fails + bool available, valid; + static const char *probe_hostname = "updates.moneropulse.org"; + auto records = get_txt_record(probe_hostname, available, valid); + if (!valid) + { + MINFO("Failed to verify DNSSEC record from " << probe_hostname << ", falling back to TCP with well known DNSSEC resolvers"); + ub_ctx_delete(m_data->m_ub_context); + m_data->m_ub_context = ub_ctx_create(); + add_anchors(m_data->m_ub_context); + dns_public_addr = tools::dns_utils::parse_dns_public(DNS_PUBLIC); + for (const auto &ip: dns_public_addr) + ub_ctx_set_fwd(m_data->m_ub_context, string_copy(ip.c_str())); + ub_ctx_set_option(m_data->m_ub_context, string_copy("do-udp:"), string_copy("no")); + ub_ctx_set_option(m_data->m_ub_context, string_copy("do-tcp:"), string_copy("yes")); + } } }