docs: link to stable releases in the bug template

Also, ask people to use a recent stable release and provide useful version information.
Inspired by #19118.

.github/ISSUE_TEMPLATE/Bug_report.md

@@ -7,8 +7,10 @@ about: A report of an error in a recent systemd version
 **systemd version the issue has been seen with**
  > …
 
-<!-- **NOTE:** Do not submit bug reports about anything but the two most recently released (non-rc) systemd versions upstream! -->
+<!-- **NOTE:** Do not submit bug reports about anything but the two most recently released *major* systemd versions upstream! -->
-<!-- See https://github.com/systemd/systemd/releases for the list of most recent releases. -->
+<!--           If there have been multiple stable releases for that major version, please consider updating to a recent one before reporting an issue. -->
+<!--           When using a distro package, please make sure that the version reported is meaningful for upstream. -->
+<!-- See https://github.com/systemd/systemd-stable/releases for the list of most recent releases. -->
 <!-- For older version please use distribution trackers (see https://systemd.io/CONTRIBUTING#filing-issues). -->
 
 **Used distribution**

src/resolve/resolved-bus.c

@@ -195,14 +195,14 @@ static void bus_method_resolve_hostname_complete(DnsQuery *q) {
                 goto finish;
         }
 
-        r = dns_query_process_cname(q);
+        r = dns_query_process_cname_many(q);
         if (r == -ELOOP) {
                 r = sd_bus_reply_method_errorf(q->bus_request, BUS_ERROR_CNAME_LOOP, "CNAME loop detected, or CNAME resolving disabled on '%s'", dns_query_string(q));
                 goto finish;
         }
         if (r < 0)
                 goto finish;
-        if (r == DNS_QUERY_RESTARTED) /* This was a cname, and the query was restarted. */
+        if (r == DNS_QUERY_CNAME) /* This was a cname, and the query was restarted. */
                 return;
 
         r = sd_bus_message_new_method_return(q->bus_request, &reply);
@@ -486,14 +486,14 @@ static void bus_method_resolve_address_complete(DnsQuery *q) {
                 goto finish;
         }
 
-        r = dns_query_process_cname(q);
+        r = dns_query_process_cname_many(q);
         if (r == -ELOOP) {
                 r = sd_bus_reply_method_errorf(q->bus_request, BUS_ERROR_CNAME_LOOP, "CNAME loop detected, or CNAME resolving disabled on '%s'", dns_query_string(q));
                 goto finish;
         }
         if (r < 0)
                 goto finish;
-        if (r == DNS_QUERY_RESTARTED) /* This was a cname, and the query was restarted. */
+        if (r == DNS_QUERY_CNAME) /* This was a cname, and the query was restarted. */
                 return;
 
         r = sd_bus_message_new_method_return(q->bus_request, &reply);
@@ -660,14 +660,14 @@ static void bus_method_resolve_record_complete(DnsQuery *q) {
                 goto finish;
         }
 
-        r = dns_query_process_cname(q);
+        r = dns_query_process_cname_many(q);
         if (r == -ELOOP) {
                 r = sd_bus_reply_method_errorf(q->bus_request, BUS_ERROR_CNAME_LOOP, "CNAME loop detected, or CNAME resolving disabled on '%s'", dns_query_string(q));
                 goto finish;
         }
         if (r < 0)
                 goto finish;
-        if (r == DNS_QUERY_RESTARTED) /* This was a cname, and the query was restarted. */
+        if (r == DNS_QUERY_CNAME) /* This was a cname, and the query was restarted. */
                 return;
 
         r = sd_bus_message_new_method_return(q->bus_request, &reply);
@@ -1107,8 +1107,8 @@ static void resolve_service_hostname_complete(DnsQuery *q) {
                 return;
         }
 
-        r = dns_query_process_cname(q);
+        r = dns_query_process_cname_many(q);
-        if (r == DNS_QUERY_RESTARTED) /* This was a cname, and the query was restarted. */
+        if (r == DNS_QUERY_CNAME) /* This was a cname, and the query was restarted. */
                 return;
 
         /* This auxiliary lookup is finished or failed, let's see if all are finished now. */
@@ -1180,14 +1180,14 @@ static void bus_method_resolve_service_complete(DnsQuery *q) {
                 goto finish;
         }
 
-        r = dns_query_process_cname(q);
+        r = dns_query_process_cname_many(q);
         if (r == -ELOOP) {
                 r = sd_bus_reply_method_errorf(q->bus_request, BUS_ERROR_CNAME_LOOP, "CNAME loop detected, or CNAME resolving disabled on '%s'", dns_query_string(q));
                 goto finish;
         }
         if (r < 0)
                 goto finish;
-        if (r == DNS_QUERY_RESTARTED) /* This was a cname, and the query was restarted. */
+        if (r == DNS_QUERY_CNAME) /* This was a cname, and the query was restarted. */
                 return;
 
         question = dns_query_question_for_protocol(q, q->answer_protocol);

src/resolve/resolved-dns-query.c

@@ -1036,7 +1036,7 @@ static int dns_query_cname_redirect(DnsQuery *q, const DnsResourceRecord *cname)
         return 0;
 }
 
-int dns_query_process_cname(DnsQuery *q) {
+int dns_query_process_cname_one(DnsQuery *q) {
         _cleanup_(dns_resource_record_unrefp) DnsResourceRecord *cname = NULL;
         DnsQuestion *question;
         DnsResourceRecord *rr;
@@ -1046,6 +1046,22 @@ int dns_query_process_cname(DnsQuery *q) {
 
         assert(q);
 
+        /* Processes a CNAME redirect if there's one. Returns one of three values:
+         *
+         * CNAME_QUERY_MATCH   → direct RR match, caller should just use the RRs in this answer (and not
+         *                       bother with any CNAME/DNAME stuff)
+         *
+         * CNAME_QUERY_NOMATCH → no match at all, neither direct nor CNAME/DNAME, caller might decide to
+         *                       restart query or take things as NODATA reply.
+         *
+         * CNAME_QUERY_CNAME   → no direct RR match, but a CNAME/DNAME match that we now followed for one step.
+         *
+         * The function might also return a failure, in particular -ELOOP if we encountered too many
+         * CNAMEs/DNAMEs in a chain or if following CNAMEs/DNAMEs was turned off.
+         *
+         * Note that this function doesn't actually restart the query. The caller can decide to do that in
+         * case of CNAME_QUERY_CNAME, though. */
+
         if (!IN_SET(q->state, DNS_TRANSACTION_SUCCESS, DNS_TRANSACTION_NULL))
                 return DNS_QUERY_NOMATCH;
 
@@ -1112,17 +1128,63 @@ int dns_query_process_cname(DnsQuery *q) {
         if (r < 0)
                 return r;
 
-        /* Let's see if the answer can already answer the new redirected question */
+        return DNS_QUERY_CNAME; /* Tell caller that we did a single CNAME/DNAME redirection step */
-        r = dns_query_process_cname(q);
+}
-        if (r != DNS_QUERY_NOMATCH)
-                return r;
 
-        /* OK, it cannot, let's begin with the new query */
+int dns_query_process_cname_many(DnsQuery *q) {
-        r = dns_query_go(q);
+        int r;
-        if (r < 0)
-                return r;
 
-        return DNS_QUERY_RESTARTED; /* We restarted the query for a new cname */
+        assert(q);
+
+        /* Follows CNAMEs through the current packet: as long as the current packet can fulfill our
+         * redirected CNAME queries we keep going, and restart the query once the current packet isn't good
+         * enough anymore. It's a wrapper around dns_query_process_cname_one() and returns the same values,
+         * but with extended semantics. Specifically:
+         *
+         * DNS_QUERY_MATCH   → as above
+         *
+         * DNS_QUERY_CNAME   → we ran into a CNAME/DNAME redirect that we could not answer from the current
+         *                     message, and thus restarted the query to resolve it.
+         *
+         * DNS_QUERY_NOMATCH → we reached the end of CNAME/DNAME chain, and there are no direct matches nor a
+         *                     CNAME/DNAME match. i.e. this is a NODATA case.
+         *
+         * Note that this function will restart the query for the caller if needed, and that's the case
+         * DNS_QUERY_CNAME is returned.
+         */
+
+        r = dns_query_process_cname_one(q);
+        if (r != DNS_QUERY_CNAME)
+                return r; /* The first redirect is special: if it doesn't answer the question that's no
+                           * reason to restart the query, we just accept this as a NODATA answer. */
+
+        for (;;) {
+                r = dns_query_process_cname_one(q);
+                if (r < 0 || r == DNS_QUERY_MATCH)
+                        return r;
+                if (r == DNS_QUERY_NOMATCH) {
+                        /* OK, so we followed one or more CNAME/DNAME RR but the existing packet can't answer
+                         * this. Let's restart the query hence, with the new question. Why the different
+                         * handling than the first chain element? Because if the server answers a direct
+                         * question with an empty answer then this is a NODATA response. But if it responds
+                         * with a CNAME chain that ultimately is incomplete (i.e. a non-empty but truncated
+                         * CNAME chain) then we better follow up ourselves and ask for the rest of the
+                         * chain. This is particular relevant since our cache will store CNAME/DNAME
+                         * redirects that we learnt about for lookups of certain DNS types, but later on we
+                         * can reuse this data even for other DNS types, but in that case need to follow up
+                         * with the final lookup of the chain ourselves with the RR type we ourselves are
+                         * interested in. */
+                        r = dns_query_go(q);
+                        if (r < 0)
+                                return r;
+
+                        return DNS_QUERY_CNAME;
+                }
+
+                /* So we found a CNAME that the existing packet already answers, again via a CNAME, let's
+                 * continue going then. */
+                assert(r == DNS_QUERY_CNAME);
+        }
 }
 
 DnsQuestion* dns_query_question_for_protocol(DnsQuery *q, DnsProtocol protocol) {

src/resolve/resolved-dns-query.h

@@ -112,7 +112,7 @@ struct DnsQuery {
 enum {
         DNS_QUERY_MATCH,
         DNS_QUERY_NOMATCH,
-        DNS_QUERY_RESTARTED,
+        DNS_QUERY_CNAME,
 };
 
 DnsQueryCandidate* dns_query_candidate_ref(DnsQueryCandidate*);
@@ -129,7 +129,8 @@ int dns_query_make_auxiliary(DnsQuery *q, DnsQuery *auxiliary_for);
 int dns_query_go(DnsQuery *q);
 void dns_query_ready(DnsQuery *q);
 
-int dns_query_process_cname(DnsQuery *q);
+int dns_query_process_cname_one(DnsQuery *q);
+int dns_query_process_cname_many(DnsQuery *q);
 
 void dns_query_complete(DnsQuery *q, DnsTransactionState state);
 

src/resolve/resolved-dns-stub.c

@@ -161,89 +161,40 @@ static int dns_stub_collect_answer_by_question(
                 DnsQuestion *question,
                 bool with_rrsig) { /* Add RRSIG RR matching each RR */
 
-        _cleanup_(dns_resource_key_unrefp) DnsResourceKey *redirected_key = NULL;
-        unsigned n_cname_redirects = 0;
         DnsAnswerItem *item;
         int r;
 
         assert(reply);
 
-        /* Copies all RRs from 'answer' into 'reply', if they match 'question'. There might be direct and
+        /* Copies all RRs from 'answer' into 'reply', if they match 'question'. */
-         * indirect matches (i.e. via CNAME/DNAME). If they have an indirect one, remember where we need to
-         * go, and restart the loop */
 
-        for (;;) {
+        DNS_ANSWER_FOREACH_ITEM(item, answer) {
-                _cleanup_(dns_resource_key_unrefp) DnsResourceKey *next_redirected_key = NULL;
 
-                DNS_ANSWER_FOREACH_ITEM(item, answer) {
+                /* We have a question, let's see if this RR matches it */
-                        DnsResourceKey *k = NULL;
+                r = dns_question_matches_rr(question, item->rr, NULL);
-
+                if (r < 0)
-                        if (redirected_key) {
+                        return r;
-                                /* There was a redirect in this packet, let's collect all matching RRs for the redirect */
+                if (!r) {
-                                r = dns_resource_key_match_rr(redirected_key, item->rr, NULL);
+                        /* Maybe there's a CNAME/DNAME in here? If so, that's an answer too */
-                                if (r < 0)
+                        r = dns_question_matches_cname_or_dname(question, item->rr, NULL);
-                                        return r;
-
-                                k = redirected_key;
-                        } else if (question) {
-                                /* We have a question, let's see if this RR matches it */
-                                r = dns_question_matches_rr(question, item->rr, NULL);
-                                if (r < 0)
-                                        return r;
-
-                                k = question->keys[0];
-                        } else
-                                r = 1; /* No question, everything matches */
-
-                        if (r == 0) {
-                                _cleanup_free_ char *target = NULL;
-
-                                /* OK, so the RR doesn't directly match. Let's see if the RR is a matching
-                                 * CNAME or DNAME */
-
-                                assert(k);
-
-                                r = dns_resource_record_get_cname_target(k, item->rr, &target);
-                                if (r == -EUNATCH)
-                                        continue; /* Not a CNAME/DNAME or doesn't match */
-                                if (r < 0)
-                                        return r;
-
-                                /* Oh, wow, this is a redirect. Let's remember where this points, and store
-                                 * it in 'next_redirected_key'. Once we finished iterating through the rest
-                                 * of the RR's we'll start again, with the redirected RR key. */
-
-                                n_cname_redirects++;
-                                if (n_cname_redirects > CNAME_REDIRECT_MAX) /* don't loop forever */
-                                        return -ELOOP;
-
-                                dns_resource_key_unref(next_redirected_key);
-
-                                /* There can only be one CNAME per name, hence no point in storing more than one here */
-                                next_redirected_key = dns_resource_key_new(k->class, k->type, target);
-                                if (!next_redirected_key)
-                                        return -ENOMEM;
-                        }
-
-                        /* Mask the section info, we want the primary answers to always go without section info, so
-                         * that it is added to the answer section when we synthesize a reply. */
-
-                        r = reply_add_with_rrsig(
-                                        reply,
-                                        item->rr,
-                                        item->ifindex,
-                                        item->flags & ~DNS_ANSWER_MASK_SECTIONS,
-                                        item->rrsig,
-                                        with_rrsig);
                         if (r < 0)
                                 return r;
+                        if (!r)
+                                continue;
                 }
 
-                if (!next_redirected_key)
+                /* Mask the section info, we want the primary answers to always go without section
-                        break;
+                 * info, so that it is added to the answer section when we synthesize a reply. */
 
-                dns_resource_key_unref(redirected_key);
+                r = reply_add_with_rrsig(
-                redirected_key = TAKE_PTR(next_redirected_key);
+                                reply,
+                                item->rr,
+                                item->ifindex,
+                                item->flags & ~DNS_ANSWER_MASK_SECTIONS,
+                                item->rrsig,
+                                with_rrsig);
+                if (r < 0)
+                        return r;
         }
 
         return 0;
@@ -323,16 +274,8 @@ static int dns_stub_assign_sections(
         if (r < 0)
                 return r;
 
-        /* Include all RRs that originate from the answer or authority sections, and aren't listed in the
+        /* Include all RRs that originate from the authority sections, and aren't already listed in the
          * answer section, in the authority section */
-        r = dns_stub_collect_answer_by_section(
-                        &q->reply_authoritative,
-                        q->answer,
-                        DNS_ANSWER_SECTION_ANSWER,
-                        q->reply_answer, NULL,
-                        edns0_do);
-        if (r < 0)
-                return r;
         r = dns_stub_collect_answer_by_section(
                         &q->reply_authoritative,
                         q->answer,
@@ -342,8 +285,16 @@ static int dns_stub_assign_sections(
         if (r < 0)
                 return r;
 
-        /* Include all RRs that originate from the additional sections in the additional section (except if
+        /* Include all RRs that originate from the answer or additional sections in the additional section
-         * already listed in the other two sections). Also add all RRs with no section marking. */
+         * (except if already listed in the other two sections). Also add all RRs with no section marking. */
+        r = dns_stub_collect_answer_by_section(
+                        &q->reply_additional,
+                        q->answer,
+                        DNS_ANSWER_SECTION_ANSWER,
+                        q->reply_answer, q->reply_authoritative,
+                        edns0_do);
+        if (r < 0)
+                return r;
         r = dns_stub_collect_answer_by_section(
                         &q->reply_additional,
                         q->answer,
@@ -771,21 +722,63 @@ static void dns_stub_query_complete(DnsQuery *q) {
 
         switch (q->state) {
 
-        case DNS_TRANSACTION_SUCCESS:
+        case DNS_TRANSACTION_SUCCESS: {
-                r = dns_query_process_cname(q);
+                bool first = true;
-                if (r == -ELOOP) { /* CNAME loop, let's send what we already have */
+
-                        log_debug_errno(r, "Detected CNAME loop, returning what we already have.");
+                for (;;) {
-                        (void) dns_stub_send_reply(q, q->answer_rcode);
+                        int cname_result;
-                        break;
+
+                        cname_result = dns_query_process_cname_one(q);
+                        if (cname_result == -ELOOP) { /* CNAME loop, let's send what we already have */
+                                log_debug_errno(r, "Detected CNAME loop, returning what we already have.");
+                                (void) dns_stub_send_reply(q, q->answer_rcode);
+                                break;
+                        }
+                        if (cname_result < 0) {
+                                log_debug_errno(cname_result, "Failed to process CNAME: %m");
+                                break;
+                        }
+
+                        if (cname_result == DNS_QUERY_NOMATCH) {
+                                /* This answer doesn't contain any RR that would answer our question
+                                 * positively, i.e. neither directly nor via CNAME. */
+
+                                if (first) /* We never followed a CNAME and the answer doesn't match our
+                                            * question at all? Then this is final, the empty answer is the
+                                            * answer. */
+                                        break;
+
+                                /* Otherwise, we already followed a CNAME once within this packet, and the
+                                 * packet doesn't answer our question. In that case let's restart the query,
+                                 * now with the redirected question. We'll */
+                                r = dns_query_go(q);
+                                if (r < 0)
+                                        log_debug_errno(r, "Failed to restart query: %m");
+
+                                return;
+                        }
+
+                        r = dns_stub_assign_sections(
+                                        q,
+                                        dns_query_question_for_protocol(q, DNS_PROTOCOL_DNS),
+                                        dns_stub_reply_with_edns0_do(q));
+                        if (r < 0) {
+                                log_debug_errno(r, "Failed to assign sections: %m");
+                                dns_query_free(q);
+                                return;
+                        }
+
+                        if (cname_result == DNS_QUERY_MATCH) /* A match? Then we are done, let's return what we got */
+                                break;
+
+                        /* We followed a CNAME. and collected the RRs that answer the redirected question
+                         * successfully. Let's not try to do this again. */
+                        assert(cname_result == DNS_QUERY_CNAME);
+                        first = false;
                 }
-                if (r < 0) {
-                        log_debug_errno(r, "Failed to process CNAME: %m");
-                        break;
-                }
-                if (r == DNS_QUERY_RESTARTED)
-                        return;
 
                 _fallthrough_;
+        }
 
         case DNS_TRANSACTION_RCODE_FAILURE:
                 (void) dns_stub_send_reply(q, q->answer_rcode);

src/resolve/resolved-varlink.c

@@ -158,14 +158,14 @@ static void vl_method_resolve_hostname_complete(DnsQuery *q) {
                 goto finish;
         }
 
-        r = dns_query_process_cname(q);
+        r = dns_query_process_cname_many(q);
         if (r == -ELOOP) {
                 r = varlink_error(q->varlink_request, "io.systemd.Resolve.CNAMELoop", NULL);
                 goto finish;
         }
         if (r < 0)
                 goto finish;
-        if (r == DNS_QUERY_RESTARTED) /* This was a cname, and the query was restarted. */
+        if (r == DNS_QUERY_CNAME) /* This was a cname, and the query was restarted. */
                 return;
 
         question = dns_query_question_for_protocol(q, q->answer_protocol);
@@ -395,14 +395,14 @@ static void vl_method_resolve_address_complete(DnsQuery *q) {
                 goto finish;
         }
 
-        r = dns_query_process_cname(q);
+        r = dns_query_process_cname_many(q);
         if (r == -ELOOP) {
                 r = varlink_error(q->varlink_request, "io.systemd.Resolve.CNAMELoop", NULL);
                 goto finish;
         }
         if (r < 0)
                 goto finish;
-        if (r == DNS_QUERY_RESTARTED) /* This was a cname, and the query was restarted. */
+        if (r == DNS_QUERY_CNAME) /* This was a cname, and the query was restarted. */
                 return;
 
         question = dns_query_question_for_protocol(q, q->answer_protocol);