On Sun, Jul 26, 2020 at 01:21:45PM +0200, Jerome Magnin wrote:
> as I was trying to reproduce the issue with DNS Service Discovery with
> SRV records reported in issue #775 I encountered a different issue.
>
> I am using bind as a dns server, and its answers contain an Authority
> field before the Additional records that can be made use of since
> 13a9232eb ("MEDIUM: dns: use Additional records from SRV responses").
> I found out that haproxy doesn't like that and would just consider the
> whole response invalid, no address being set for my servers.
>
> I've attached a patch to test for the type and just skip to the next
> record, and it seems to work. I'm not sure it's the proper fix, as we
> might want to test for the presence of an Authority field.
>
> Note that the same config "works" before that commit. I understand
> haproxy makes a lot more DNS requests before that commit, but what I
> mean is that users migrating from earlier versions to 2.2 can have their
> service break because of this.
Please find a proper fix attached. We already know if we have entries in
the Authority section (dns_p->header.nscount > 0), so just skip them
when they are present and only use the Additional records.
Jérôme
>From f77c279a8a3d40629d00238155b7adf941f1ccb6 Mon Sep 17 00:00:00 2001
From: Jerome Magnin <[email protected]>
Date: Sun, 26 Jul 2020 12:13:12 +0200
Subject: [PATCH] BUG/MAJOR: dns: don't treat Authority records as an error
Support for DNS Service Discovery by means of SRV records was enhanced with
commit 13a9232eb ("MEDIUM: dns: use Additional records from SRV responses")
to use the content of the answers Additional records when present.
If there are Authority records before the Additional records we mistakenly
treat that as an invalid response. To fix this, just ignore the Authority
section if it exist and skip to the Additional records.
---
src/dns.c | 25 +++++++++++++++++++++++++
1 file changed, 25 insertions(+)
diff --git a/src/dns.c b/src/dns.c
index 6a8ab831c..292739b2a 100644
--- a/src/dns.c
+++ b/src/dns.c
@@ -1044,6 +1044,31 @@ static int dns_validate_dns_response(unsigned char
*resp, unsigned char *bufend,
if (dns_query->type != DNS_RTYPE_SRV)
goto skip_parsing_additional_records;
+ for (i = 0; i < dns_p->header.nscount; i++) {
+ offset = 0;
+ len = dns_read_name(resp, bufend, reader, tmpname,
DNS_MAX_NAME_SIZE,
+ &offset, 0);
+ if (len == 0) {
+ continue;
+ }
+
+ if (reader + offset + 10 >= bufend)
+ goto invalid_resp;
+
+ reader += offset;
+ /* skip 2 bytes for class */
+ reader += 2;
+ /* skip 2 bytes for type */
+ reader += 2;
+ /* skip 2 bytes for ttl */
+ reader += 4;
+ /* read data len */
+ len = reader[0] * 256 + reader[1];
+ reader += 2;
+ if (reader + len >= bufend)
+ goto invalid_resp;
+ reader += len;
+ }
nb_saved_records = 0;
for (i = 0; i < dns_p->header.arcount; i++) {
if (reader >= bufend)
--
2.27.0
