It's not going to be simple I'm afraid, at least for the original
problem! "scmp_sys_resolver close_range" will quickly test whether
current seccomp has support for close_range (prints "-1" if not
supported, "436" otherwise - at least on x86_64.) Ubuntu seccomp
maintainers have been pretty happy SRUing this sort of thing before -
it's a running problem, and the changes are trivial.

Outline of a reproducer for my original problem would be something like:

1. download and unpack 
https://partner-images.canonical.com/core/focal/current/ubuntu-focal-core-cloudimg-amd64-root.tar.gz
2. cd to the rootfs directory and start a container with "systemd-nspawn"
3. Add podman/buildah PPA:
. /etc/os-release
echo "deb 
https://download.opensuse.org/repositories/devel:/kubic:/libcontainers:/stable/xUbuntu_${VERSION_ID}/
 /" | sudo tee /etc/apt/sources.list.d/devel:kubic:libcontainers:stable.list
curl -L 
"https://download.opensuse.org/repositories/devel:/kubic:/libcontainers:/stable/xUbuntu_${VERSION_ID}/Release.key";
 | sudo apt-key add -
sudo apt-get update
sudo apt-get -y upgrade
4. apt-get -y install buildah
5. create scratch container and copy in busybox
ctr=$(buildah from scratch)
buildah copy $ctr /bin/busybox
6. check EOF handling
echo foo | buildah run $ctr /busybox cat

Without the patch, this should fail to return to the prompt, as the missing 
syscall seems to interfere with buildah's ability to to process EOF; with the 
patch it should return to the prompt.
In the event of failure there should also be messages logged about 
"close_range" being unsupported.

Above is untested - I'll double-check it and flesh it out when
time/health permits, but hopefully it has some utility. There are
probably simpler test cases involving docker, but that's not my area...

-- 
You received this bug notification because you are a member of Ubuntu
Touch seeded packages, which is subscribed to libseccomp in Ubuntu.
https://bugs.launchpad.net/bugs/1944436

Title:
  Please backport support for "close_range" syscall

Status in libseccomp package in Ubuntu:
  New

Bug description:
  Please backport support for the "close_range" syscall .. may be as
  simple as cherrypicking

  
https://github.com/seccomp/libseccomp/commit/01e5750e7c84bb14e5a5410c924bed519209db06

  from upstream. I've hit problems running buildah in a systemd-nspawn
  container, but this will probably affect people trying to run modern
  code in other container systems as well, e.g. docker.

  ProblemType: Bug
  DistroRelease: Ubuntu 20.04
  Package: libseccomp2 2.5.1-1ubuntu1~20.04.1
  ProcVersionSignature: Ubuntu 5.4.0-84.94-generic 5.4.133
  Uname: Linux 5.4.0-84-generic x86_64
  ApportVersion: 2.20.11-0ubuntu27.20
  Architecture: amd64
  CasperMD5CheckResult: skip
  CurrentDesktop: Xpra
  Date: Tue Sep 21 15:10:54 2021
  InstallationDate: Installed on 2017-01-08 (1717 days ago)
  InstallationMedia: Xubuntu 16.04 LTS "Xenial Xerus" - Release amd64 
(20160420.1)
  SourcePackage: libseccomp
  UpgradeStatus: Upgraded to focal on 2021-09-02 (19 days ago)

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