From 716b9360452bcebd89d48faa895375fa3360b9ed Mon Sep 17 00:00:00 2001 From: Aram Sargsyan Date: Tue, 21 Jan 2025 13:20:12 +0000 Subject: [PATCH] Implement sig0key-checks-limit and sig0message-checks-limit Previously a hard-coded limitation of maximum two key or message verification checks were introduced when checking the message's SIG(0) signature. It was done in order to protect against possible DoS attacks. The logic behind choosing the number two was that more than one key should only be required only during key rotations, and in that case two keys are enough. But later it became apparent that there are other use cases too where even more keys are required, see issue number #5050 in GitLab. This change introduces two new configuration options for the views, sig0key-checks-limit and sig0message-checks-limit, which define how many keys are allowed to be checked to find a matching key, and how many message verifications are allowed to take place once a matching key has been found. The latter protects against expensive cryptographic operations when there are keys with colliding tags and algorithm numbers, with default being 2, and the former protects against a bit less expensive key parsing operations and defaults to 16. --- bin/named/config.c | 2 ++ bin/named/server.c | 13 ++++++++++ bin/tests/system/upforwd/setup.sh | 2 +- bin/tests/system/upforwd/tests.sh | 8 +++--- doc/misc/options | 4 +++ lib/dns/include/dns/view.h | 2 ++ lib/dns/message.c | 43 ++++++++++++++++++++++++------- lib/isccfg/namedconf.c | 2 ++ 8 files changed, 62 insertions(+), 14 deletions(-) diff --git a/bin/named/config.c b/bin/named/config.c index e3aaecdd3e..bdc1722470 100644 --- a/bin/named/config.c +++ b/bin/named/config.c @@ -111,6 +111,8 @@ options {\n\ session-keyname local-ddns;\n\ startup-notify-rate 20;\n\ sig0checks-quota 1;\n\ + sig0key-checks-limit 16;\n\ + sig0message-checks-limit 2;\n\ statistics-file \"named.stats\";\n\ tcp-advertised-timeout 300;\n\ tcp-clients 150;\n\ diff --git a/bin/named/server.c b/bin/named/server.c index 3dce65e359..14bf29d826 100644 --- a/bin/named/server.c +++ b/bin/named/server.c @@ -4703,6 +4703,19 @@ configure_view(dns_view_t *view, dns_viewlist_t *viewlist, cfg_obj_t *config, dns_view_settransports(view, transports); dns_transport_list_detach(&transports); + /* + * Configure SIG(0) check limits when matching a DNS message to a view. + */ + obj = NULL; + result = named_config_get(maps, "sig0key-checks-limit", &obj); + INSIST(result == ISC_R_SUCCESS); + view->sig0key_checks_limit = cfg_obj_asuint32(obj); + + obj = NULL; + result = named_config_get(maps, "sig0message-checks-limit", &obj); + INSIST(result == ISC_R_SUCCESS); + view->sig0message_checks_limit = cfg_obj_asuint32(obj); + /* * Configure the view's TSIG keys. */ diff --git a/bin/tests/system/upforwd/setup.sh b/bin/tests/system/upforwd/setup.sh index 0df66cb6f2..7fddf0175c 100644 --- a/bin/tests/system/upforwd/setup.sh +++ b/bin/tests/system/upforwd/setup.sh @@ -44,7 +44,7 @@ fi cat_i ns1/example2-toomanykeys.db -for i in 1 2 3; do +for i in 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17; do keyname=$($KEYGEN -q -n HOST -a ${DEFAULT_ALGORITHM} -T KEY sig0.example2-toomanykeys 2>/dev/null) if test -n "$keyname"; then cat $keyname.key >>ns1/example2-toomanykeys.db diff --git a/bin/tests/system/upforwd/tests.sh b/bin/tests/system/upforwd/tests.sh index 5e1f4550bd..5591aabb67 100644 --- a/bin/tests/system/upforwd/tests.sh +++ b/bin/tests/system/upforwd/tests.sh @@ -460,7 +460,7 @@ EOF ret=0 good=0 bad=0 - for i in 1 2 3; do + for i in 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17; do keyname=$(cat keyname$i) $NSUPDATE -d -D -k $keyname.private -- - <nsupdate.out.test$n.$i 2>&1 && good=$((good + 1)) || bad=$((bad + 1)) local 10.53.0.1 @@ -470,9 +470,9 @@ EOF send EOF done - # There are three keys in the zone but named checks the signature using - # maximum two keys, so one of these updates should have been failed. - [ $good = 2 ] && [ $bad = 1 ] || ret=1 + # There are 17 keys in the zone but by default named checks maximum 16 keys + # to find a matching key, so one of these updates should have been failed. + [ $good = 16 ] && [ $bad = 1 ] || ret=1 if [ $ret != 0 ]; then echo_i "failed"; fi status=$((status + ret)) n=$((n + 1)) diff --git a/doc/misc/options b/doc/misc/options index f49c0a8800..3fa81f4bae 100644 --- a/doc/misc/options +++ b/doc/misc/options @@ -279,6 +279,8 @@ options { sig-validity-interval [ ]; // obsolete sig0checks-quota ; // experimental sig0checks-quota-exempt { ; ... }; // experimental + sig0key-checks-limit ; + sig0message-checks-limit ; stale-answer-client-timeout ( disabled | off | ); stale-answer-enable ; stale-answer-ttl ; @@ -573,6 +575,8 @@ view [ ] { sig-signing-signatures ; sig-signing-type ; sig-validity-interval [ ]; // obsolete + sig0key-checks-limit ; + sig0message-checks-limit ; stale-answer-client-timeout ( disabled | off | ); stale-answer-enable ; stale-answer-ttl ; diff --git a/lib/dns/include/dns/view.h b/lib/dns/include/dns/view.h index aa87fa6c9a..266ba49d6c 100644 --- a/lib/dns/include/dns/view.h +++ b/lib/dns/include/dns/view.h @@ -179,6 +179,8 @@ struct dns_view { uint32_t fail_ttl; dns_badcache_t *failcache; unsigned int udpsize; + uint32_t sig0key_checks_limit; + uint32_t sig0message_checks_limit; uint32_t maxrrperset; uint32_t maxtypepername; uint16_t max_queries; diff --git a/lib/dns/message.c b/lib/dns/message.c index e174cf8a68..bdb3044a78 100644 --- a/lib/dns/message.c +++ b/lib/dns/message.c @@ -3279,12 +3279,7 @@ dns_message_checksig(dns_message_t *msg, dns_view_t *view) { dns_rdata_sig_t sig; dns_rdataset_t keyset; isc_result_t result; - /* - * In order to protect from a possible DoS attack, we are - * going to check at most two KEY RRs. - */ - const size_t max_keys = 2; - size_t n; + uint32_t key_checks, message_checks; result = dns_rdataset_first(msg->sig0); INSIST(result == ISC_R_SUCCESS); @@ -3325,8 +3320,25 @@ dns_message_checksig(dns_message_t *msg, dns_view_t *view) { result = dns_rdataset_first(&keyset); INSIST(result == ISC_R_SUCCESS); - for (n = 0; result == ISC_R_SUCCESS && n < max_keys; - n++, result = dns_rdataset_next(&keyset)) + /* + * In order to protect from a possible DoS attack, this function + * supports limitations on how many keyid checks and how many + * key checks (message verifications using a matched key) are + * going to be allowed. + */ + const uint32_t max_key_checks = + view->sig0key_checks_limit > 0 + ? view->sig0key_checks_limit + : UINT32_MAX; + const uint32_t max_message_checks = + view->sig0message_checks_limit > 0 + ? view->sig0message_checks_limit + : UINT32_MAX; + + for (key_checks = 0, message_checks = 0; + result == ISC_R_SUCCESS && key_checks < max_key_checks && + message_checks < max_message_checks; + key_checks++, result = dns_rdataset_next(&keyset)) { dst_key_t *key = NULL; @@ -3353,8 +3365,21 @@ dns_message_checksig(dns_message_t *msg, dns_view_t *view) { if (result == ISC_R_SUCCESS) { break; } + message_checks++; } - if (result == ISC_R_NOMORE || n == max_keys) { + if (result == ISC_R_NOMORE) { + result = DNS_R_KEYUNAUTHORIZED; + } else if (key_checks == max_key_checks) { + isc_log_write(ISC_LOGCATEGORY_GENERAL, + DNS_LOGMODULE_MESSAGE, ISC_LOG_DEBUG(3), + "sig0key-checks-limit reached when " + "trying to check a message signature"); + result = DNS_R_KEYUNAUTHORIZED; + } else if (message_checks == max_message_checks) { + isc_log_write(ISC_LOGCATEGORY_GENERAL, + DNS_LOGMODULE_MESSAGE, ISC_LOG_DEBUG(3), + "sig0message-checks-limit reached when " + "trying to check a message signature"); result = DNS_R_KEYUNAUTHORIZED; } diff --git a/lib/isccfg/namedconf.c b/lib/isccfg/namedconf.c index 6319d0df8f..85d1c531c0 100644 --- a/lib/isccfg/namedconf.c +++ b/lib/isccfg/namedconf.c @@ -2122,6 +2122,8 @@ static cfg_clausedef_t view_clauses[] = { { "rrset-order", &cfg_type_rrsetorder, 0 }, { "send-cookie", &cfg_type_boolean, 0 }, { "servfail-ttl", &cfg_type_duration, 0 }, + { "sig0key-checks-limit", &cfg_type_uint32, 0 }, + { "sig0message-checks-limit", &cfg_type_uint32, 0 }, { "sortlist", &cfg_type_bracketed_aml, CFG_CLAUSEFLAG_ANCIENT }, { "stale-answer-enable", &cfg_type_boolean, 0 }, { "stale-answer-client-timeout", &cfg_type_staleanswerclienttimeout,