gvproxy on macOS fails to start without internet connection

[srcshelton]

Issue Description

I realised during a flight that gvproxy on macOS requires a working internet connection in order for podman machine start to succeed.

Running podman --log-level trace machine start shows the failing command as:

$ /opt/homebrew/Cellar/podman/5.3.1/libexec/podman/gvproxy -debug -mtu 1500 -ssh-port 61529 -listen-vfkit unixgram:///var/folders/<xx>/<xxxx>/T/podman/podman-machine-default-gvproxy.sock -forward-dest /run/podman/podman.sock -forward-user root -forward-identity /Users/<user>/.local/share/containers/podman/machine/machine -forward-sock /var/folders/<xx>/<xxxx>/T/podman/podman-machine-default-api.sock -pid-file /var/folders/<xx>/<xxxx>/T/podman/gvproxy.pid -log-file /var/folders/<xx>/<xxxx>/T/podman/gvproxy.log
panic: runtime error: index out of range [0] with length 0

goroutine 33 [running]:
github.com/containers/gvisor-tap-vsock/pkg/services/dns.getDNSHostAndPort()
	/private/tmp/podman--gvproxy-20241122-5354-gcocwn/gvisor-tap-vsock-0.8.0/pkg/services/dns/dns_config_unix.go:15 +0x94
github.com/containers/gvisor-tap-vsock/pkg/services/dns.newDNSHandler({0x14000130000, 0x2, 0x2})
	/private/tmp/podman--gvproxy-20241122-5354-gcocwn/gvisor-tap-vsock-0.8.0/pkg/services/dns/dns.go:29 +0x2c
github.com/containers/gvisor-tap-vsock/pkg/services/dns.New({0x104712780, 0x1400015e2c0}, {0x10470cf38, 0x1400015e340}, {0x14000130000?, 0x0?, 0x0?})
	/private/tmp/podman--gvproxy-20241122-5354-gcocwn/gvisor-tap-vsock-0.8.0/pkg/services/dns/dns.go:166 +0x3c
github.com/containers/gvisor-tap-vsock/pkg/virtualnetwork.dnsServer(0x1400011a1a0, 0x14000101008)
	/private/tmp/podman--gvproxy-20241122-5354-gcocwn/gvisor-tap-vsock-0.8.0/pkg/virtualnetwork/services.go:80 +0x250
github.com/containers/gvisor-tap-vsock/pkg/virtualnetwork.addServices(0x1400011a1a0, 0x14000101008, 0x14000140000)
	/private/tmp/podman--gvproxy-20241122-5354-gcocwn/gvisor-tap-vsock-0.8.0/pkg/virtualnetwork/services.go:32 +0x268
github.com/containers/gvisor-tap-vsock/pkg/virtualnetwork.New(0x1400011a1a0)
	/private/tmp/podman--gvproxy-20241122-5354-gcocwn/gvisor-tap-vsock-0.8.0/pkg/virtualnetwork/virtualnetwork.go:71 +0x374
main.run({0x10470ea10, 0x14000052460}, 0x140000ae900, 0x0?, {0x0, 0x0, 0x0?})
	/private/tmp/podman--gvproxy-20241122-5354-gcocwn/gvisor-tap-vsock-0.8.0/cmd/gvproxy/main.go:314 +0x3c
main.main.func3()
	/private/tmp/podman--gvproxy-20241122-5354-gcocwn/gvisor-tap-vsock-0.8.0/cmd/gvproxy/main.go:265 +0x44
golang.org/x/sync/errgroup.(*Group).Go.func1()
	/private/tmp/podman--gvproxy-20241122-5354-gcocwn/gvisor-tap-vsock-0.8.0/vendor/golang.org/x/sync/errgroup/errgroup.go:78 +0x54
created by golang.org/x/sync/errgroup.(*Group).Go in goroutine 1
	/private/tmp/podman--gvproxy-20241122-5354-gcocwn/gvisor-tap-vsock-0.8.0/vendor/golang.org/x/sync/errgroup/errgroup.go:75 +0x98

My reading of this is that gvproxy won't start without DNS - it also appears to be a problem if WiFi is turned-off on a machine without an active ethernet (or other) network connection.

In this case, connecting to the airline's captive portal (which only redirects to a payment page, rather than providing a full internet service) was enough to allow the pre-existing podman machine to start correctly.

Steps to reproduce the issue

Steps to reproduce the issue

1. Create a podman machine;
2. Stop it;
3. Disconnect network interfaces;
4. Attempt to podman machine start.

Describe the results you received

panic: runtime error: index out of range [0] with length 0 from gvproxy.

Describe the results you expected

The podman machine VM should have started even without active networking (surely?)

podman info output

host:
  arch: arm64
  buildahVersion: 1.38.0
  cgroupControllers:
  - cpuset
  - cpu
  - io
  - memory
  - pids
  - rdma
  - misc
  cgroupManager: systemd
  cgroupVersion: v2
  conmon:
    package: conmon-2.1.12-2.fc40.aarch64
    path: /usr/bin/conmon
    version: 'conmon version 2.1.12, commit: '
  cpuUtilization:
    idlePercent: 97.27
    systemPercent: 1.66
    userPercent: 1.07
  cpus: 4
  databaseBackend: sqlite
  distribution:
    distribution: fedora
    variant: coreos
    version: "40"
  eventLogger: journald
  freeLocks: 2048
  hostname: localhost.localdomain
  idMappings:
    gidmap: null
    uidmap: null
  kernel: 6.11.3-200.fc40.aarch64
  linkmode: dynamic
  logDriver: journald
  memFree: 7285112832
  memTotal: 7717347328
  networkBackend: netavark
  networkBackendInfo:
    backend: netavark
    dns:
      package: aardvark-dns-1.12.2-2.fc40.aarch64
      path: /usr/libexec/podman/aardvark-dns
      version: aardvark-dns 1.12.2
    package: netavark-1.12.2-1.fc40.aarch64
    path: /usr/libexec/podman/netavark
    version: netavark 1.12.2
  ociRuntime:
    name: crun
    package: crun-1.17-1.fc40.aarch64
    path: /usr/bin/crun
    version: |-
      crun version 1.17
      commit: 000fa0d4eeed8938301f3bcf8206405315bc1017
      rundir: /run/crun
      spec: 1.0.0
      +SYSTEMD +SELINUX +APPARMOR +CAP +SECCOMP +EBPF +CRIU +LIBKRUN +WASM:wasmedge +YAJL
  os: linux
  pasta:
    executable: /usr/bin/pasta
    package: passt-0^20240906.g6b38f07-1.fc40.aarch64
    version: |
      pasta 0^20240906.g6b38f07-1.fc40.aarch64-pasta
      Copyright Red Hat
      GNU General Public License, version 2 or later
        <https://www.gnu.org/licenses/old-licenses/gpl-2.0.html>
      This is free software: you are free to change and redistribute it.
      There is NO WARRANTY, to the extent permitted by law.
  remoteSocket:
    exists: true
    path: unix:///run/podman/podman.sock
  rootlessNetworkCmd: pasta
  security:
    apparmorEnabled: false
    capabilities: CAP_CHOWN,CAP_DAC_OVERRIDE,CAP_FOWNER,CAP_FSETID,CAP_KILL,CAP_NET_BIND_SERVICE,CAP_SETFCAP,CAP_SETGID,CAP_SETPCAP,CAP_SETUID,CAP_SYS_CHROOT
    rootless: false
    seccompEnabled: true
    seccompProfilePath: /usr/share/containers/seccomp.json
    selinuxEnabled: true
  serviceIsRemote: true
  slirp4netns:
    executable: /usr/bin/slirp4netns
    package: slirp4netns-1.2.2-2.fc40.aarch64
    version: |-
      slirp4netns version 1.2.2
      commit: 0ee2d87523e906518d34a6b423271e4826f71faf
      libslirp: 4.7.0
      SLIRP_CONFIG_VERSION_MAX: 4
      libseccomp: 2.5.5
  swapFree: 0
  swapTotal: 0
  uptime: 0h 1m 44.00s
  variant: v8
plugins:
  authorization: null
  log:
  - k8s-file
  - none
  - passthrough
  - journald
  network:
  - bridge
  - macvlan
  - ipvlan
  volume:
  - local
registries:
  search:
  - docker.io
store:
  configFile: /usr/share/containers/storage.conf
  containerStore:
    number: 0
    paused: 0
    running: 0
    stopped: 0
  graphDriverName: overlay
  graphOptions:
    overlay.imagestore: /usr/lib/containers/storage
    overlay.mountopt: nodev,metacopy=on
  graphRoot: /var/lib/containers/storage
  graphRootAllocated: 39123398656
  graphRootUsed: 14462476288
  graphStatus:
    Backing Filesystem: xfs
    Native Overlay Diff: "false"
    Supports d_type: "true"
    Supports shifting: "true"
    Supports volatile: "true"
    Using metacopy: "true"
  imageCopyTmpDir: /var/tmp
  imageStore:
    number: 0
  runRoot: /run/containers/storage
  transientStore: false
  volumePath: /var/lib/containers/storage/volumes
version:
  APIVersion: 5.3.1
  Built: 1732147200
  BuiltTime: Wed Nov 20 17:00:00 2024
  GitCommit: ""
  GoVersion: go1.22.7
  Os: linux
  OsArch: linux/arm64
  Version: 5.3.1

Podman in a container

No

Privileged Or Rootless

None

Upstream Latest Release

Yes

Additional environment details

macOS 15.2

Additional information

No response