Failed to detect shell correctly in container image build case

[mortyccp]

The shell detection will check the process of the host instead of stopping inside the container image build environment
The following is the ps output inside the container build step
It will detect the shell as bash but the image being used don't have bash

PID   USER     TIME  COMMAND
    1 root      0:00 /usr/bin/bash
   24 root      0:00 sh -c (/scripts-926-2646660/detect_shell_script /scripts-926-2646660/step_script 2>&1 | tee -a /logs-926-2646660/output.log) &
   25 root      0:00 /usr/bin/bash /scripts-926-2646660/step_script
   26 root      0:00 tee -a /logs-926-2646660/output.log
   30 root      0:00 /usr/bin/bash /scripts-926-2646660/step_script
   72 root      0:00 buildah build
   80 root      0:27 {3} buildah-in-a-user-namespace build
  367 root      0:00 {5} buildah-chroot-runtime
  375 root      0:00 {5} buildah-chroot-exec /bin/sh -c ps
  383 root      0:00 ps

[milesj]

@mortyccp Do you have an example dockerfile I can test with?

[mortyccp]

@milesj Sure, I have prepared a reproduce repo https://github.com/mortyccp/reproduces/tree/moon-shell-detection-in-container-build

[milesj]

I've looked into this a bit, but I'm not sure what the fix would be in starbase. Since we're not "in" the docker container, the .dockerenv file doesn't exist, and /proc/self/cgroup doesn't have docker either, so I can't introduce any conditional logic.

However, adding ENV SHELL=sh to the Dockerfile fixed the problem.