dns_msg_parse_reply() fails for response from DNS64 service

[benpicco]

Description

TREX provides a public DNS64+NAT64 service that allows to reach IPv4 only hosts from an IPv6 only network.

The responses from this nameserver do confuse dns_msg_parse_reply() though.
It will fail in different places on subsequent requests which hints to a message parsing bug.

Steps to reproduce the issue

Configure the DNS64 nameserver and enable sock_dns:

USEMODULE += sock_dns
USEMODULE += auto_init_sock_dns

CFLAGS += -DCONFIG_AUTO_INIT_SOCK_DNS_SERVER_ADDR=\"2001:67c:2b0::6\"
CFLAGS += -DCONFIG_DNS_MSG_LEN=256 # response msg is 202 bytes

You can either run this on a board with a direct internet connection or on native if your host is connected to an IPv6 network. In his case, run

sudo dist/tools/tapsetup/tapsetup -u enp0s25

(in this case enp0s25 is the uplink ethernet interface)

Expected results

We can resolve any IPv4 only hostname.

$ dig @2001:67c:2b0::6 global.azure-devices-provisioning.net aaaa

; <<>> DiG 9.18.18-0ubuntu2-Ubuntu <<>> @2001:67c:2b0::6 global.azure-devices-provisioning.net aaaa
; (1 server found)
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 7471
;; flags: qr rd ra; QUERY: 1, ANSWER: 3, AUTHORITY: 0, ADDITIONAL: 1

;; OPT PSEUDOSECTION:
; EDNS: version: 0, flags:; udp: 512
;; QUESTION SECTION:
;global.azure-devices-provisioning.net. IN AAAA

;; ANSWER SECTION:
global.azure-devices-provisioning.net. 569 IN CNAME id-prod-global-endpoint.trafficmanager.net.
id-prod-global-endpoint.trafficmanager.net. 59 IN CNAME	idsu-prod-am-001-su-az.westeurope.cloudapp.azure.com.
idsu-prod-am-001-su-az.westeurope.cloudapp.azure.com. 10 IN AAAA 2001:67c:2b0:db32::2871:b0aa

;; Query time: 96 msec
;; SERVER: 2001:67c:2b0::6#53(2001:67c:2b0::6) (UDP)
;; WHEN: Wed Feb 07 16:30:56 CET 2024
;; MSG SIZE  rcvd: 213

Actual results

The response from global.azure-devices-provisioning.net can't be parsed

2024-02-07 16:17:20,552 # > ping global.azure-devices-provisioning.net
2024-02-07 16:17:20,750 # DNS: got 202 bytes:
2024-02-07 16:17:20,759 # 0x00, 0x00, 0x81, 0x80, 0x00, 0x01, 0x00, 0x03, 0x00, 0x00, 0x00, 0x00, 0x06, 0x67, 0x6c, 0x6f, 0x62, 0x61, 0x6c, 0x1a, 0x61, 0x7a, 0x75, 0x72, 0x65, 0x2d, 0x64, 0x65, 0x76, 0x69, 0x63, 0x65, 0x73, 0x2d, 0x70, 0x72, 0x6f, 0x76, 0x69, 0x73, 0x69, 0x6f, 0x6e, 0x69, 0x6e, 0x67, 0x03, 0x6e, 0x65, 0x74, 0x00, 0x00, 0x1c, 0x00, 0x01, 0xc0, 0x0c, 0x00, 0x05, 0x00, 0x01, 0x00, 0x00, 0x01, 0x61, 0x00, 0x29, 0x17, 0x69, 0x64, 0x2d, 0x70, 0x72, 0x6f, 0x64, 0x2d, 0x67, 0x6c, 0x6f, 0x62, 0x61, 0x6c, 0x2d, 0x65, 0x6e, 0x64, 0x70, 0x6f, 0x69, 0x6e, 0x74, 0x0e, 0x74, 0x72, 0x61, 0x66, 0x66, 0x69, 0x63, 0x6d, 0x61, 0x6e, 0x61, 0x67, 0x65, 0x72, 0xc0, 0x2e, 0xc0, 0x43, 0x00, 0x05, 0x00, 0x01, 0x00, 0x00, 0x00, 0x5a, 0x00, 0x36, 0x16, 0x69, 0x64, 0x73, 0x75, 0x2d, 0x70, 0x72, 0x6f, 0x64, 0x2d, 0x61, 0x6d, 0x2d, 0x30, 0x30, 0x31, 0x2d, 0x73, 0x75, 0x2d, 0x61, 0x7a, 0x0a, 0x77, 0x65, 0x73, 0x74, 0x65, 0x75, 0x72, 0x6f, 0x70, 0x65, 0x08, 0x63, 0x6c, 0x6f, 0x75, 0x64, 0x61, 0x70, 0x70, 0x05, 0x61, 0x7a, 0x75, 0x72, 0x65, 0x03, 0x63, 0x6f, 0x6d, 0x00, 0xc0, 0x78, 0x00, 0x1c, 0x00, 0x01, 0x00, 0x00, 0x00, 0x0a, 0x00, 0x10, 0x20, 0x01, 0x06, 0x7c, 0x02, 0xb0, 0xdb, 0x32, 0x00, 0x00, 0x00, 0x01, 0x28, 0x71, 0xb0, 0xaa, 
2024-02-07 16:17:20,786 # DNS: got 202 bytes:
2024-02-07 16:17:20,791 # 0x00, 0x00, 0x81, 0x80, 0x00, 0x01, 0x00, 0x03, 0x00, 0x00, 0x00, 0x00, 0x06, 0x67, 0x6c, 0x6f, 0x62, 0x61, 0x6c, 0x1a, 0x61, 0x7a, 0x75, 0x72, 0x65, 0x2d, 0x64, 0x65, 0x76, 0x69, 0x63, 0x65, 0x73, 0x2d, 0x70, 0x72, 0x6f, 0x76, 0x69, 0x73, 0x69, 0x6f, 0x6e, 0x69, 0x6e, 0x67, 0x03, 0x6e, 0x65, 0x74, 0x00, 0x00, 0x1c, 0x00, 0x01, 0xc0, 0x0c, 0x00, 0x05, 0x00, 0x01, 0x00, 0x00, 0x01, 0x61, 0x00, 0x29, 0x17, 0x69, 0x64, 0x2d, 0x70, 0x72, 0x6f, 0x64, 0x2d, 0x67, 0x6c, 0x6f, 0x62, 0x61, 0x6c, 0x2d, 0x65, 0x6e, 0x64, 0x70, 0x6f, 0x69, 0x6e, 0x74, 0x0e, 0x74, 0x72, 0x61, 0x66, 0x66, 0x69, 0x63, 0x6d, 0x61, 0x6e, 0x61, 0x67, 0x65, 0x72, 0xc0, 0x2e, 0xc0, 0x43, 0x00, 0x05, 0x00, 0x01, 0x00, 0x00, 0x00, 0x5a, 0x00, 0x36, 0x16, 0x69, 0x64, 0x73, 0x75, 0x2d, 0x70, 0x72, 0x6f, 0x64, 0x2d, 0x61, 0x6d, 0x2d, 0x30, 0x30, 0x31, 0x2d, 0x73, 0x75, 0x2d, 0x61, 0x7a, 0x0a, 0x77, 0x65, 0x73, 0x74, 0x65, 0x75, 0x72, 0x6f, 0x70, 0x65, 0x08, 0x63, 0x6c, 0x6f, 0x75, 0x64, 0x61, 0x70, 0x70, 0x05, 0x61, 0x7a, 0x75, 0x72, 0x65, 0x03, 0x63, 0x6f, 0x6d, 0x00, 0xc0, 0x78, 0x00, 0x1c, 0x00, 0x01, 0x00, 0x00, 0x00, 0x0a, 0x00, 0x10, 0x20, 0x01, 0x06, 0x7c, 0x02, 0xb0, 0xdb, 0x32, 0x00, 0x00, 0x00, 0x01, 0x28, 0x71, 0xb0, 0xaa, 
2024-02-07 16:17:20,791 # can't resolve global.azure-devices-provisioning.net

While others work fine

2024-02-07 16:24:51,504 # > ping github.com
2024-02-07 16:24:51,626 # DNS: got 56 bytes:
2024-02-07 16:24:51,627 # 0x00, 0x00, 0x81, 0x80, 0x00, 0x01, 0x00, 0x01, 0x00, 0x00, 0x00, 0x00, 0x06, 0x67, 0x69, 0x74, 0x68, 0x75, 0x62, 0x03, 0x63, 0x6f, 0x6d, 0x00, 0x00, 0x1c, 0x00, 0x01, 0xc0, 0x0c, 0x00, 0x1c, 0x00, 0x01, 0x00, 0x00, 0x00, 0x3c, 0x00, 0x10, 0x20, 0x01, 0x06, 0x7c, 0x02, 0xb0, 0xdb, 0x32, 0x00, 0x00, 0x00, 0x01, 0x8c, 0x52, 0x79, 0x03, 
2024-02-07 16:24:51,698 # 12 bytes from 2001:67c:2b0:db32:0:1:8c52:7903: icmp_seq=0 ttl=46 time=71.737 ms
2024-02-07 16:24:52,699 # 12 bytes from 2001:67c:2b0:db32:0:1:8c52:7903: icmp_seq=1 ttl=46 time=71.654 ms
2024-02-07 16:24:53,700 # 12 bytes from 2001:67c:2b0:db32:0:1:8c52:7903: icmp_seq=2 ttl=46 time=72.748 ms
2024-02-07 16:24:53,700 # 
2024-02-07 16:24:53,701 # --- github.com PING statistics ---
2024-02-07 16:24:53,702 # 3 packets transmitted, 3 packets received, 0% packet loss
2024-02-07 16:24:53,702 # round-trip min/avg/max = 71.654/72.046/72.748 ms

Versions

RIOT master, discovered in #20223