panic with DNS SRV query on 1.19.1

[alexdulin]

Overview of the Issue

Consul 1.19.1 can still panic on certain DNS queries, despite other issues that have been resolved.

---

Reproduction Steps

1. In one terminal, run consul agent -dev -client 0.0.0.0 -bind 0.0.0.0 -recursor 8.8.8.8 -advertise '{{ GetPrivateIP }}'
2. In another terminal, run dig -p 8600 foo.virtual.consul SRV

The result:

panic: runtime error: invalid memory address or nil pointer dereference
[signal SIGSEGV: segmentation violation code=0x1 addr=0x0 pc=0x26c3bfa]

goroutine 243 [running]:
github.com/hashicorp/consul/agent/dns.messageSerializer.serialize({}, 0xc0012fbb48)
	github.com/hashicorp/consul/agent/dns/message_serializer.go:85 +0x4fa
github.com/hashicorp/consul/agent/dns.(*Router).handleRequestRecursively(0xc0012ae120, 0xc000a566c0, {{0x0, 0x0}, {0x0, 0x0}, {0x0, 0x0}}, 0xc0004b4310, {0x54a5ac8, ...}, ...)
	github.com/hashicorp/consul/agent/dns/router.go:276 +0x97b
github.com/hashicorp/consul/agent/dns.(*Router).HandleRequest(0xc0012ae120, 0xc000a566c0, {{0x0, 0x0}, {0x0, 0x0}, {0x0, 0x0}}, {0x54a5ac8, 0xc001350b10})
	github.com/hashicorp/consul/agent/dns/router.go:188 +0x42a
github.com/hashicorp/consul/agent/dns.(*Router).ServeDNS(0xc0012ae120, {0x54d4ad0, 0xc000e87480}, 0xc000a566c0)
	github.com/hashicorp/consul/agent/dns/router.go:315 +0x53
github.com/miekg/dns.(*Server).serveDNS(0xc0012a4240, {0xc0012be000, 0x3b, 0xffff}, 0xc000e87480)
	github.com/miekg/dns@v1.1.50/server.go:659 +0x42a
github.com/miekg/dns.(*Server).serveUDPPacket(0xc0012a4240, 0xc00129a320, {0xc0012be000, 0x3b, 0xffff}, {0x54cfd70, 0xc00128e068}, 0xc000f90640, {0x0, 0x0})
	github.com/miekg/dns@v1.1.50/server.go:603 +0x1a5
created by github.com/miekg/dns.(*Server).serveUDP in goroutine 172
	github.com/miekg/dns@v1.1.50/server.go:533 +0x405

Consul info for both Client and Server

Consul v1.19.1
Revision 9f62fb41
Build Date 2024-07-11T14:47:27Z
Protocol 2 spoken by default, understands 2 to 3 (agent will automatically use protocol >2 when speaking to compatible agents)

Operating system and Environment details

Linux 5.19.0-50-generic 50-Ubuntu SMP PREEMPT_DYNAMIC Mon Jul 10 18:24:29 UTC 2023 x86_64 x86_64 x86_64 GNU/Linux

[jmurret]

This is resolved with #21598 which reverts the experimental v2 dns and will be available in 1.19.2.