IP address following the "--gateway" argument in pasta_options fails to parse

[teichner]

Issue Description

My ~/.config/containers/containers.conf is set to the following:

[network]
pasta_options = ["--gateway", "10.10.0.171"]

Trying to run podman unshare --rootless-netns /bin/bash fails with

Error: rootless netns: cleanup: 1 error occurred:
	* rootless netns: kill network process: strconv.Atoi: parsing "": invalid syntax

If I replace --gateway with --dns, the config is fine. If I instead follow --gateway with a malformed IP address, parsing fails as expected with "Invalid gateway address".

Podman info:

host:
  arch: amd64
  buildahVersion: 1.43.0
  cgroupControllers:
  - cpu
  - memory
  - pids
  cgroupManager: systemd
  cgroupVersion: v2
  conmon:
    package: conmon-2.2.1-2.fc43.x86_64
    path: /usr/bin/conmon
    version: 'conmon version 2.2.1, commit: '
  cpuUtilization:
    idlePercent: 99.77
    systemPercent: 0.15
    userPercent: 0.08
  cpus: 8
  databaseBackend: sqlite
  distribution:
    distribution: fedora
    variant: cloud
    version: "43"
  emulatedArchitectures:
  - linux/arm
  - linux/arm64
  - linux/arm64be
  - linux/loong64
  - linux/mips
  - linux/mips64
  - linux/ppc
  - linux/ppc64
  - linux/ppc64le
  - linux/riscv32
  - linux/riscv64
  - linux/s390x
  eventLogger: journald
  freeLocks: 2020
  hostname: xxxxxx
  idMappings:
    gidmap:
    - container_id: 0
      host_id: 1002
      size: 1
    - container_id: 1
      host_id: 1100
      size: 100
    - container_id: 101
      host_id: 589824
      size: 65536
    uidmap:
    - container_id: 0
      host_id: 1002
      size: 1
    - container_id: 1
      host_id: 1100
      size: 100
    - container_id: 101
      host_id: 589824
      size: 65536
  kernel: 6.19.10-200.fc43.x86_64
  linkmode: dynamic
  logDriver: journald
  memFree: 23657955328
  memTotal: 25178247168
  networkBackend: netavark
  networkBackendInfo:
    backend: netavark
    defaultNetwork: podman
    dns:
      package: aardvark-dns-1.17.0-1.fc43.x86_64
      path: /usr/libexec/podman/aardvark-dns
      version: aardvark-dns 1.17.0
    package: netavark-1.17.2-1.fc43.x86_64
    path: /usr/libexec/podman/netavark
    version: netavark 1.17.2
  ociRuntime:
    name: crun
    package: crun-1.27-1.fc43.x86_64
    path: /usr/bin/crun
    version: |-
      crun version 1.27
      commit: a718a92cc9a94955a5a550b6fdec1378c247ec50
      rundir: /run/user/1002/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-0^20260120.g386b5f5-1.fc43.x86_64
    version: |
      pasta 0^20260120.g386b5f5-1.fc43.x86_64-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: /run/user/1002/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: true
    seccompEnabled: true
    seccompProfilePath: /usr/share/containers/seccomp.json
    selinuxEnabled: true
  serviceIsRemote: false
  slirp4netns:
    executable: ""
    package: ""
    version: ""
  swapFree: 8589930496
  swapTotal: 8589930496
  uptime: 0h 35m 29.00s
  variant: ""
plugins:
  authorization: null
  log:
  - k8s-file
  - none
  - passthrough
  - journald
  network:
  - bridge
  - macvlan
  - ipvlan
  volume:
  - local
registries:
  search:
  - registry.fedoraproject.org
  - registry.access.redhat.com
  - docker.io
store:
  configFile: /var/home/podman/.config/containers/storage.conf
  containerStore:
    number: 2
    paused: 0
    running: 0
    stopped: 2
  graphDriverName: overlay
  graphOptions: {}
  graphRoot: /var/home/podman/.local/share/containers/storage
  graphRootAllocated: 33203138560
  graphRootUsed: 7828791296
  graphStatus:
    Backing Filesystem: btrfs
    Native Overlay Diff: "true"
    Supports d_type: "true"
    Supports shifting: "false"
    Supports volatile: "true"
    Using metacopy: "false"
  imageCopyTmpDir: /var/tmp
  imageStore:
    number: 13
  runRoot: /run/user/1002/containers
  transientStore: false
  volumePath: /var/home/podman/.local/share/containers/storage/volumes
version:
  APIVersion: 5.8.1
  BuildOrigin: Fedora Project
  Built: 1773187200
  BuiltTime: Wed Mar 11 00:00:00 2026
  GitCommit: c6077f645788743258a1a749f8005b4fb3cbe533
  GoVersion: go1.25.7 X:nodwarf5
  Os: linux
  OsArch: linux/amd64
  Version: 5.8.1

[danishprakash]

That's indeed a bug when pasta creates or leaves an empty file, but podman (c/common) assumes there will always be a PID if the file exists, which seems not to be the case.

https://github.com/containers/container-libs/blob/f0ddf1a745bb52c26889dcd69499c2dd9d4f40c1/common/libnetwork/internal/rootlessnetns/netns_linux.go#L650-L656

That being said, it looks like we might be masking an underlying error if the cleanup fails. cc/ @sbrivio-rh

[Luap99]

Did you actually make sure the gateway is valid compared to the default subnet pasta picks?

In particular what happens if you pass that one the cli

$ podman run --network pasta:--gateway,1.1.1.1 quay.io/libpod/testimage:20241011 true
Error: pasta failed with exit code 1:
Couldn't set IPv4 route(s) in guest: Network is unreachable

Trying with --network pasta:--gateway,1.1.1.1,--pid,/tmp/pasta.pid shows that it fails to startup and created an empty pid file and thus podman does indeed fail to read it.
I guess we could handle this in podman to ignore empty pid file there.

[teichner]

Did you actually make sure the gateway is valid compared to the default subnet pasta picks?

No; notwithstanding the empty PID bug, there must be a misunderstanding on my part. My goal is to funnel all traffic from rootless containers on a podman network through a different gateway on the host's subnet, without affecting the host's own routing. I assumed that because pasta reflects the host's configuration into podman's network namespace, this new gateway would be visible from within, and it would be a matter of changing the namespace's default route. However, changes to the routing table were not reflected in my containers, and trying to assign a gateway through config resulted in the issue you see here.

Now that I think about it, there's no NAT between this namespace and the host through pasta, so I don't imagine custom routing could be done this way. How could I better approach this? I'm still learning.

In particular what happens if you pass that one the cli

$ podman run --network pasta:--gateway,1.1.1.1 quay.io/libpod/testimage:20241011 true
Error: pasta failed with exit code 1:
Couldn't set IPv4 route(s) in guest: Network is unreachable

Trying with --network pasta:--gateway,1.1.1.1,--pid,/tmp/pasta.pid shows that it fails to startup and created an empty pid file and thus podman does indeed fail to read it.
I guess we could handle this in podman to ignore empty pid file there.

Running this command gives me the same response you've copied here. Thanks all.