podman cp creates files in container only as root user

[awerlang]

Is this a BUG REPORT or FEATURE REQUEST? (leave only one on its own line)

/kind bug

Description

podman cp creates files in container as root user. When container is created with options --userns --user files kept the uid from host system prior to v3.

Steps to reproduce the issue:

1. (shell 1) podman run --rm -u $(id -u) --userns=keep-id -it registry.opensuse.org/opensuse/leap

2. (shell 2) podman cp $XAUTHORITY CONTAINERID:/tmp/.Xauthority

3. (shell 1) cat /tmp/.Xauthority

Describe the results you received:

cat: /tmp/.Xauthority: Permission denied

Describe the results you expected:

File is accessible.

Additional information you deem important (e.g. issue happens only occasionally):

Rootless.
Used to work until v2.2.1.
Tried podman unshare podman mount but mount point was empty?!

Output of podman version:

Version:      3.0.1
API Version:  3.0.0
Go Version:   go1.13.15
Built:        Tue Feb 23 21:00:00 2021
OS/Arch:      linux/amd64

Output of podman info --debug:

host:
  arch: amd64
  buildahVersion: 1.19.4
  cgroupManager: cgroupfs
  cgroupVersion: v1
  conmon:
    package: conmon-2.0.26-1.1.x86_64
    path: /usr/bin/conmon
    version: 'conmon version 2.0.26, commit: unknown'
  cpus: 8
  distribution:
    distribution: '"opensuse-tumbleweed"'
    version: "20210302"
  eventLogger: journald
  hostname: localhost
  idMappings:
    gidmap:
    - container_id: 0
      host_id: 100
      size: 1
    - container_id: 1
      host_id: 100000
      size: 65536
    uidmap:
    - container_id: 0
      host_id: 1000
      size: 1
    - container_id: 1
      host_id: 100000
      size: 65536
  kernel: 5.10.16-1-default
  linkmode: dynamic
  memFree: 264986624
  memTotal: 16669970432
  ociRuntime:
    name: runc
    package: runc-1.0.0~rc93-1.2.x86_64
    path: /usr/bin/runc
    version: |-
      runc version 1.0.0-rc93
      commit: 12644e614e25b05da6fd08a38ffa0cfe1903fdec
      spec: 1.0.2-dev
      go: go1.13.15
      libseccomp: 2.5.0
  os: linux
  remoteSocket:
    path: /run/user/1000/podman/podman.sock
  security:
    apparmorEnabled: false
    capabilities: CAP_AUDIT_WRITE,CAP_CHOWN,CAP_DAC_OVERRIDE,CAP_FOWNER,CAP_FSETID,CAP_KILL,CAP_MKNOD,CAP_NET_BIND_SERVICE,CAP_NET_RAW,CAP_SETFCAP,CAP_SETGID,CAP_SETPCAP,CAP_SETUID,CAP_SYS_CHROOT
    rootless: true
    seccompEnabled: true
    selinuxEnabled: false
  slirp4netns:
    executable: /usr/bin/slirp4netns
    package: slirp4netns-1.1.8-1.2.x86_64
    version: |-
      slirp4netns version 1.1.8
      commit: unknown
      libslirp: 4.4.0
      SLIRP_CONFIG_VERSION_MAX: 3
      libseccomp: 2.5.0
  swapFree: 10727510016
  swapTotal: 10737414144
  uptime: 14h 13m 10.97s (Approximately 0.58 days)
registries:
  search:
  - registry.opensuse.org
  - docker.io
store:
  configFile: /home/andre/.config/containers/storage.conf
  containerStore:
    number: 3
    paused: 0
    running: 0
    stopped: 3
  graphDriverName: overlay
  graphOptions:
    overlay.mount_program:
      Executable: /usr/bin/fuse-overlayfs
      Package: fuse-overlayfs-1.4.0-1.1.x86_64
      Version: |-
        fusermount3 version: 3.10.2
        fuse-overlayfs: version 1.4
        FUSE library version 3.10.2
        using FUSE kernel interface version 7.31
  graphRoot: /home/andre/.local/share/containers/storage
  graphStatus:
    Backing Filesystem: btrfs
    Native Overlay Diff: "false"
    Supports d_type: "true"
    Using metacopy: "false"
  imageStore:
    number: 62
  runRoot: /run/user/1000/containers
  volumePath: /home/andre/.local/share/containers/storage/volumes
version:
  APIVersion: 3.0.0
  Built: 1614124800
  BuiltTime: Tue Feb 23 21:00:00 2021
  GitCommit: ""
  GoVersion: go1.13.15
  OsArch: linux/amd64
  Version: 3.0.1

Package info (e.g. output of rpm -q podman or apt list podman):

podman-3.0.1-1.1.x86_64

Have you tested with the latest version of Podman and have you checked the Podman Troubleshooting Guide?

Yes

Additional environment details (AWS, VirtualBox, physical, etc.):

[mheon]

@vrothberg PTAL