Root privilege escalation(?)

[jeroendev-one]

Issue Description

Running Rootless podman on RHEL8:

podman.x86_64                                        4:4.9.4-12.module+el8.10.0+22202+761b9a65  @rhel-8-for-x86_64-appstream-rpms 

With these options in the /etc/containers/storage.conf

[storage]
driver = "overlay"
runroot = "/run/containers/storage"
graphroot = "/var/lib/containers/storage"
rootless_storage_path = "$HOME/.local/share/containers/storage"
[storage.options]
additionalimagestores = [
]
pull_options = {enable_partial_images = "false", use_hard_links = "false", ostree_repos=""}
[storage.options.overlay]
mount_program = "/usr/bin/fuse-overlayfs"
mountopt = "nodev,metacopy=on"

I noticed while trying to cleanup container images to save up space, podman allowed me to become root by using podman unshare:

uid=1100(runner-1) gid=1100(runner-1) groups=1100(runner-1) context=unconfined_u:unconfined_r:unconfined_t:s0-s0:c0.c1023
[runner-1@build01 ~]$ podman unshare
WARN[0000] Failed to get rootless runtime dir for DefaultAPIAddress: lstat /run/user/0: no such file or directory 
[root@build01 ~]# id
uid=0(root) gid=0(root) groups=0(root) context=unconfined_u:unconfined_r:container_runtime_t:s0-s0:c0.c1023

It's not a fully privileged root, but I found it strange that it does elevate to root.

Steps to reproduce the issue

Steps to reproduce the issue

1. Install podman same version and storage config
2. Become a rootless user
3. Execute podman unshare

Describe the results you received

It elevates the privileges to uid 0 (root)

Describe the results you expected

It should stay the same user

podman info output

host:
  arch: amd64
  buildahVersion: 1.33.8
  cgroupControllers: []
  cgroupManager: cgroupfs
  cgroupVersion: v1
  conmon:
    package: conmon-2.1.10-1.module+el8.10.0+22202+761b9a65.x86_64
    path: /usr/bin/conmon
    version: 'conmon version 2.1.10, commit: 148bf229a807d6e44637491c5f02ea75d0700397'
  cpuUtilization:
    idlePercent: 97.62
    systemPercent: 0.53
    userPercent: 1.86
  cpus: 12
  databaseBackend: sqlite
  distribution:
    distribution: rhel
    version: "8.10"
  eventLogger: file
  freeLocks: 2040
  hostname: build01.local
  idMappings:
    gidmap:
    - container_id: 0
      host_id: 1100
      size: 1
    - container_id: 1
      host_id: 100000
      size: 165537
    uidmap:
    - container_id: 0
      host_id: 1100
      size: 1
    - container_id: 1
      host_id: 100000
      size: 165537
  kernel: 4.18.0-553.16.1.el8_10.x86_64
  linkmode: dynamic
  logDriver: k8s-file
  memFree: 7291482112
  memTotal: 24979623936
  networkBackend: cni
  networkBackendInfo:
    backend: cni
    dns:
      package: podman-plugins-4.9.4-12.module+el8.10.0+22202+761b9a65.x86_64
      path: /usr/libexec/cni/dnsname
      version: |-
        CNI dnsname plugin
        version: 1.4.0-dev
        commit: unknown
        CNI protocol versions supported: 0.1.0, 0.2.0, 0.3.0, 0.3.1, 0.4.0, 1.0.0
    package: containernetworking-plugins-1.4.0-5.module+el8.10.0+22202+761b9a65.x86_64
    path: /usr/libexec/cni
  ociRuntime:
    name: runc
    package: runc-1.1.12-4.module+el8.10.0+22202+761b9a65.x86_64
    path: /usr/bin/runc
    version: |-
      runc version 1.1.12
      spec: 1.0.2-dev
      go: go1.21.7 (Red Hat 1.21.7-2.module+el8.10.0+21638+b01be198)
      libseccomp: 2.5.2
  os: linux
  pasta:
    executable: ""
    package: ""
    version: ""
  remoteSocket:
    exists: true
    path: /run/user/1100/podman/podman.sock
  security:
    apparmorEnabled: false
    capabilities: CAP_NET_RAW,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: /bin/slirp4netns
    package: slirp4netns-1.2.3-1.module+el8.10.0+22202+761b9a65.x86_64
    version: |-
      slirp4netns version 1.2.3
      commit: c22fde291bb35b354e6ca44d13be181c76a0a432
      libslirp: 4.4.0
      SLIRP_CONFIG_VERSION_MAX: 3
      libseccomp: 2.5.2
  swapFree: 8313630720
  swapTotal: 8396992512
  uptime: 187h 40m 2.00s (Approximately 7.79 days)
  variant: ""
plugins:
  authorization: null
  log:
  - k8s-file
  - none
  - passthrough
  - journald
  network:
  - bridge
  - macvlan
  - ipvlan
  volume:
  - local
registries:
  search:
  - registry.access.redhat.com
  - registry.redhat.io
  - docker.io
store:
  configFile: /home/runner-1/.config/containers/storage.conf
  containerStore:
    number: 0
    paused: 0
    running: 0
    stopped: 0
  graphDriverName: overlay
  graphOptions: {}
  graphRoot: /home/runner-1/.local/share/containers/storage
  graphRootAllocated: 1089800765440
  graphRootUsed: 446398717952
  graphStatus:
    Backing Filesystem: xfs
    Native Overlay Diff: "true"
    Supports d_type: "true"
    Supports shifting: "false"
    Supports volatile: "true"
    Using metacopy: "false"
  imageCopyTmpDir: /var/tmp
  imageStore:
    number: 23
  runRoot: /run/user/1100/containers
  transientStore: false
  volumePath: /home/runner-1/.local/share/containers/storage/volumes
version:
  APIVersion: 4.9.4-rhel
  Built: 1723116282
  BuiltTime: Thu Aug  8 13:24:42 2024
  GitCommit: ""
  GoVersion: go1.21.7 (Red Hat 1.21.7-2.module+el8.10.0+21638+b01be198)
  Os: linux
  OsArch: linux/amd64
  Version: 4.9.4-rhel

Podman in a container

No

Privileged Or Rootless

Rootless

Upstream Latest Release

Yes

Additional environment details

No response

Additional information

No response

[sbrivio-rh]

It's not a fully privileged root, but I found it strange that it does elevate to root.

That's not root, it's UID 0 in a separate user namespace, but id(1) doesn't know that. See user_namespaces(7).

[rhatdan]

This is intended behavior and not a root privilege escalation, just the way User Namespaces work. You are root of your usernamespace but really just a process running as your normal UID.