CVE-2018-14629 dns: fix CNAME loop prevention using counter regression

The loop prevention should only be done for CNAME records!

Otherwise we truncate the answer records for A, AAAA or
SRV queries, which is a bad idea if you have more than 20 DCs.

BUG: https://bugzilla.samba.org/show_bug.cgi?id=13600

Signed-off-by: Stefan Metzmacher <metze@samba.org>
Reviewed-by: Douglas Bagnall <douglas.bagnall@catalyst.net.nz>
Autobuild-User(master): Andrew Bartlett <abartlet@samba.org>
Autobuild-Date(master): Tue Dec  4 08:52:29 CET 2018 on sn-devel-144

diff --git a/selftest/knownfail.d/dns b/selftest/knownfail.d/dns
index 4bf01bdd89ea4f9c99feb80cf4ba3b40ba6d9262..ec345372046a31ac833aaf13c41f4443f8f29f3a 100644 (file)
--- a/selftest/knownfail.d/dns
+++ b/selftest/knownfail.d/dns
@@ -87,9 +87,3 @@ samba.tests.dns.__main__.TestSimpleQueries.test_one_SOA_query\(rodc:local\)
 ^samba.tests.dns.__main__.TestComplexQueries.test_cname_limit\(rodc:local\)
 ^samba.tests.dns.__main__.TestComplexQueries.test_cname_any_query\(vampire_dc:local\)
 ^samba.tests.dns.__main__.TestComplexQueries.test_cname_any_query\(rodc:local\)
-
-# These all fail until the next patch
-^samba.tests.dns.__main__.TestComplexQueries.test_cname_limit
-^samba.tests.dns.__main__.TestComplexQueries.test_record_limit_SRV
-^samba.tests.dns.__main__.TestComplexQueries.test_record_limit_AAAA
-^samba.tests.dns.__main__.TestComplexQueries.test_record_limit_A

diff --git a/source4/dns_server/dns_query.c b/source4/dns_server/dns_query.c
index 65faeac3b6a4c89657e33122ebfe493d41b9efb7..b75fabe7e827591ada313365509991db9c773a70 100644 (file)
--- a/source4/dns_server/dns_query.c
+++ b/source4/dns_server/dns_query.c
@@ -388,7 +388,8 @@ static struct tevent_req *handle_authoritative_send(
        TALLOC_CTX *mem_ctx, struct tevent_context *ev,
        struct dns_server *dns, const char *forwarder,
        struct dns_name_question *question,
-       struct dns_res_rec **answers, struct dns_res_rec **nsrecs);
+       struct dns_res_rec **answers, struct dns_res_rec **nsrecs,
+       size_t cname_depth);
 static WERROR handle_authoritative_recv(struct tevent_req *req);
 
 struct handle_dnsrpcrec_state {
@@ -404,7 +405,8 @@ static struct tevent_req *handle_dnsrpcrec_send(
        struct dns_server *dns, const char *forwarder,
        const struct dns_name_question *question,
        struct dnsp_DnssrvRpcRecord *rec,
-       struct dns_res_rec **answers, struct dns_res_rec **nsrecs)
+       struct dns_res_rec **answers, struct dns_res_rec **nsrecs,
+       size_t cname_depth)
 {
        struct tevent_req *req, *subreq;
        struct handle_dnsrpcrec_state *state;
@@ -420,7 +422,7 @@ static struct tevent_req *handle_dnsrpcrec_send(
        state->answers = answers;
        state->nsrecs = nsrecs;
 
-       if (talloc_array_length(*answers) >= MAX_Q_RECURSION_DEPTH) {
+       if (cname_depth >= MAX_Q_RECURSION_DEPTH) {
                tevent_req_done(req);
                return tevent_req_post(req, ev);
        }
@@ -465,7 +467,8 @@ static struct tevent_req *handle_dnsrpcrec_send(
        if (dns_authoritative_for_zone(dns, new_q->name)) {
                subreq = handle_authoritative_send(
                        state, ev, dns, forwarder, new_q,
-                       state->answers, state->nsrecs);
+                       state->answers, state->nsrecs,
+                       cname_depth + 1);
                if (tevent_req_nomem(subreq, req)) {
                        return tevent_req_post(req, ev);
                }
@@ -549,6 +552,8 @@ struct handle_authoritative_state {
 
        struct dns_res_rec **answers;
        struct dns_res_rec **nsrecs;
+
+       size_t cname_depth;
 };
 
 static void handle_authoritative_done(struct tevent_req *subreq);
@@ -557,7 +562,8 @@ static struct tevent_req *handle_authoritative_send(
        TALLOC_CTX *mem_ctx, struct tevent_context *ev,
        struct dns_server *dns, const char *forwarder,
        struct dns_name_question *question,
-       struct dns_res_rec **answers, struct dns_res_rec **nsrecs)
+       struct dns_res_rec **answers, struct dns_res_rec **nsrecs,
+       size_t cname_depth)
 {
        struct tevent_req *req, *subreq;
        struct handle_authoritative_state *state;
@@ -575,6 +581,7 @@ static struct tevent_req *handle_authoritative_send(
        state->forwarder = forwarder;
        state->answers = answers;
        state->nsrecs = nsrecs;
+       state->cname_depth = cname_depth;
 
        werr = dns_name2dn(dns, state, question->name, &dn);
        if (tevent_req_werror(req, werr)) {
@@ -595,7 +602,8 @@ static struct tevent_req *handle_authoritative_send(
        subreq = handle_dnsrpcrec_send(
                state, state->ev, state->dns, state->forwarder,
                state->question, &state->recs[state->recs_done],
-               state->answers, state->nsrecs);
+               state->answers, state->nsrecs,
+               state->cname_depth);
        if (tevent_req_nomem(subreq, req)) {
                return tevent_req_post(req, ev);
        }
@@ -627,7 +635,8 @@ static void handle_authoritative_done(struct tevent_req *subreq)
        subreq = handle_dnsrpcrec_send(
                state, state->ev, state->dns, state->forwarder,
                state->question, &state->recs[state->recs_done],
-               state->answers, state->nsrecs);
+               state->answers, state->nsrecs,
+               state->cname_depth);
        if (tevent_req_nomem(subreq, req)) {
                return;
        }
@@ -1000,7 +1009,8 @@ struct tevent_req *dns_server_process_query_send(
 
                subreq = handle_authoritative_send(
                        state, ev, dns, (forwarders == NULL ? NULL : forwarders[0]),
-                       &in->questions[0], &state->answers, &state->nsrecs);
+                       &in->questions[0], &state->answers, &state->nsrecs,
+                       0); /* cname_depth */
                if (tevent_req_nomem(subreq, req)) {
                        return tevent_req_post(req, ev);
                }
@@ -1102,7 +1112,8 @@ static void dns_server_process_query_got_auth(struct tevent_req *subreq)
                subreq = handle_authoritative_send(state, state->ev, state->dns,
                                                   state->forwarders->forwarder,
                                                   state->question, &state->answers,
-                                                  &state->nsrecs);
+                                                  &state->nsrecs,
+                                                  0); /* cname_depth */
 
                if (tevent_req_nomem(subreq, req)) {
                        return;