[Bug 2037682] Re: curtin in-target issues if process uses /proc and new pid namespace is used

[Dan Bungert]

We believe this issue has been resolved in Subiquity 24.04.1, which can
be obtained on the Ubuntu 24.04 LTS ISO or as a snap refresh.

A curtin release containing this fix will be available at a later date.

** Changed in: curtin
       Status: Fix Committed => Fix Released

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Title:
  curtin in-target issues if process uses /proc and new pid namespace is
  used

Status in curtin:
  Fix Released

Bug description:
  Hi Team,

  we are facing an issue when running commands "in-target" that rely on /proc/ information, but have been
  launched in a new pid namespace (curtin behavior). 

  One example is installing a dkms package using late-commands:

  autoinstall:
    late-commands:
     - TARGET_MOUNT_POINT=/target curtin in-target -- apt install -y r8168-dkms
     
  The dkms script (/usr/sbin/dkms) has a loop dependent on the the /proc/$pid of a spawned process:

  (eval "$1" >/dev/null 2>&1) & pid=$!
  while [ -d /proc/$pid ]; do

  But the /proc is a bind to the default namespace /proc, and lists all the processes, but the new PID
  is in the new namespace, so /proc/$pid will refer to a different process or will be non-existent.

  Inspecting curtin behavior, here is what is happening:

  ChrootableTarget will mount, by default, "/dev", "/proc", "/run", "/sys" to the target system with 
  the --bind flag, before running the command, and after that, the command is executed using:

  ['unshare', '--fork', '--pid', '--', 'chroot', '/target', 'command']

  The process pid and /proc will not show the same information.

  Trying some possible solutions here, I thought about adding --mount-proc=/target/proc to unshare, 
  but that fails:

  unshare --mount-proc=/target/proc --fork --pid -- chroot /target hostname
  unshare: cannot change /target/proc filesystem propagation: Invalid argument

  I see that subp accepts a unshare_pid=False that would avoid creating a new namespace 
  (and solving the problem for these scenarios), but I found no way to pass it to the curtin 
  in-target command.

  Another option would be create the new namespace, mount proc, and run
  the command afterward.

  Any suggestions on how to solve this?

  Thanks

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