Incorrect behaviour in creating loop devices

[AndrewLipscomb]

Issue Description

Repeat of #17715 - adding a bit more detail so it gets picked up this time. I have confirmed the behaviour when

• Running podman as root, and
• Using --privileged=true, and
• Adding --cap-add SYS_ADMIN explicitly

Steps to reproduce the issue

Same repro instructions - you'll need a mountable image of some sort to work with, and you should ensure you have no /dev/loop* devices already present. In my case - I start with no /dev/loopX devices.

If there are /dev/loopX devices extant but not in use (ie: visible via ls /dev/loop* but not visible in losetup -la) then the issue won't appear as the container will reuse the extant loopX device. The container has to both create a new /dev/loopX device, and attempt to use it for the bug to appear.

sudo podman run --rm -it --privileged=true --cap-add SYS_ADMIN docker.io/library/debian:13 bash

In the container, make a test ext4 fs to mount

apt-get update
apt-get install e2fsprogs
dd if=/dev/zero of=/test_ext4 bs=1M count=0 seek=512 status=none
mkfs.ext4 -F  "/test_ext4"

Then - try to mount this ext4

mount -o loop,rw /test_ext4 /mnt
mount: /mnt: failed to setup loop device for /test_ext4.

Inside the container - there is no /dev/loop0. On my host system - /dev/loop0 exists after the mount command is run.

It seems the container can create the /dev/loop0 device, but can't pick it up after creation

Describe the results you received

Can't see /dev/loopX after creation in the container - despite being able to create it from the container

Describe the results you expected

Should see /dev/loopX after creation in the container - OR should see an error when trying to create the loop device if that is more appropriate behaviour.

The issue is more that it can create it, but not read/use it. That's confusing. Should be all-or-nothing

podman info output

Run via sudo podman info as this is for rootful containers

host:
  arch: amd64
  buildahVersion: 1.42.2
  cgroupControllers:
  - cpuset
  - cpu
  - io
  - memory
  - hugetlb
  - pids
  - rdma
  - misc
  - dmem
  cgroupManager: systemd
  cgroupVersion: v2
  conmon:
    package: conmon-1:2.1.13-1
    path: /usr/bin/conmon
    version: 'conmon version 2.1.13, commit: 82de887596ed8ee6d9b2ee85e4f167f307bb569b'
  cpuUtilization:
    idlePercent: 97.95
    systemPercent: 0.68
    userPercent: 1.38
  cpus: 16
  databaseBackend: sqlite
  distribution:
    distribution: arch
    version: unknown
  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: 2047
  hostname: archlinux
  idMappings:
    gidmap: null
    uidmap: null
  kernel: 6.18.4-arch1-1
  linkmode: dynamic
  logDriver: journald
  memFree: 89026641920
  memTotal: 96639836160
  networkBackend: netavark
  networkBackendInfo:
    backend: netavark
    dns:
      package: aardvark-dns-1.17.0-1
      path: /usr/lib/podman/aardvark-dns
      version: aardvark-dns 1.17.0
    package: netavark-1.17.1-1
    path: /usr/lib/podman/netavark
    version: netavark 1.17.1
  ociRuntime:
    name: runc
    package: runc-1.4.0-1
    path: /usr/bin/runc
    version: |-
      runc version 1.4.0
      spec: 1.3.0
      go: go1.25.4 X:nodwarf5
      libseccomp: 2.6.0
  os: linux
  pasta:
    executable: /usr/bin/pasta
    package: passt-2025_12_23.2ba9fd5-1
    version: |
      pasta 2025_12_23.2ba9fd5
      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/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: /etc/containers/seccomp.json
    selinuxEnabled: false
  serviceIsRemote: false
  slirp4netns:
    executable: ""
    package: ""
    version: ""
  swapFree: 34359734272
  swapTotal: 34359734272
  uptime: 0h 10m 40.00s
  variant: ""
plugins:
  authorization: null
  log:
  - k8s-file
  - none
  - passthrough
  - journald
  network:
  - bridge
  - macvlan
  - ipvlan
  volume:
  - local
registries: {}
store:
  configFile: /etc/containers/storage.conf
  containerStore:
    number: 1
    paused: 0
    running: 0
    stopped: 1
  graphDriverName: overlay
  graphOptions:
    overlay.mountopt: nodev
  graphRoot: /var/lib/containers/storage
  graphRootAllocated: 989293707264
  graphRootUsed: 727788290048
  graphStatus:
    Backing Filesystem: btrfs
    Native Overlay Diff: "false"
    Supports d_type: "true"
    Supports shifting: "true"
    Supports volatile: "true"
    Using metacopy: "true"
  imageCopyTmpDir: /var/tmp
  imageStore:
    number: 10
  runRoot: /run/containers/storage
  transientStore: false
  volumePath: /var/lib/containers/storage/volumes
version:
  APIVersion: 5.7.1
  Built: 1765447754
  BuiltTime: Thu Dec 11 21:09:14 2025
  GitCommit: f845d14e941889ba4c071f35233d09b29d363c75
  GoVersion: go1.25.5 X:nodwarf5
  Os: linux
  OsArch: linux/amd64
  Version: 5.7.1

Podman in a container

No

Privileged Or Rootless

Privileged

Upstream Latest Release

No

Additional environment details

Stock Arch Linux install, nothing custom

Additional information

No response

[AndrewLipscomb]

I have attempted this with docker as well and reproduced the same result - so this may not be at the container engine level but somewhere deeper.