scubainit ignores SIGPIPE

[haboustak]

The new scubainit included in version 2.13.0 ignores SIGPIPE, which is then inherited by any process that scuba runs. This behavior is included as a side-effect of the Rust entrypoint. See rust-lang/rust #62569

Here's a test case that was shared with me recently and demonstrates the behavior change from 2.12.0 to 2.13.0:

$ scuba --image debian:12 sh -c "yes | echo abcd"
abcd
yes: standard output: Broken pipe

Also, to show that SIGPIPE is ignored in 2.13.0:

$ scuba --image debian:12 cat /proc/1/status | grep "Sig"
SigQ:	1/31475
SigPnd:	0000000000000000
SigBlk:	0000000000000000
SigIgn:	0000000000001000
SigCgt:	0000000000010002

I think the correct behavior for scuba is to reset SIGPIPE to SIG_DFL.

[JonathonReinhart]

I believe this is handled by #253, but I haven't looked at it yet.

[haboustak]

Ah yes. I came here looking for an issue and not a PR. I’d imagine the compiler flag will fix it.

[JonathonReinhart]

If I understand the problem statement correctly:

• The default disposition of SIGPIPE is Term: signal(7)
• From pipe(7):

  If all file descriptors referring to the read end of a pipe have been closed, then a write(2) will cause a SIGPIPE signal to be generated for the calling process. If the calling process is ignoring this signal, then write(2) fails with the error EPIPE.

• So normally, yes is terminated by SIGPIPE with no error output (before write returns) when the reader closes the pipe.
• But with scubainit ignoring SIGPIPE (due to Rust startup code), and yes inheriting it, yes instead sees write return with EPIPE, resulting in an error message before termination.

Please correct me if I got any of that wrong.

[JonathonReinhart]

demo.sh:

#!/bin/bash
vers=(2.12.0 2.13.0)
for ver in ${vers[@]}; do
    echo "======== Scuba ${ver} ========"
    venv="scuba-${ver}"
    python3 -m venv $venv || exit $?
    ${venv}/bin/pip install "scuba==${ver}" || exit $?
    ${venv}/bin/scuba --version
    ${venv}/bin/scuba --image debian:12 sh -c "yes | echo abcd"
done

Output:

$ ./demo.sh
======== Scuba 2.12.0 ========
Requirement already satisfied: scuba==2.12.0 in ./scuba-2.12.0/lib/python3.11/site-packages (2.12.0)
Requirement already satisfied: PyYAML in ./scuba-2.12.0/lib/python3.11/site-packages (from scuba==2.12.0) (6.0.1)
scuba 2.12.0
abcd
======== Scuba 2.13.0 ========
Requirement already satisfied: scuba==2.13.0 in ./scuba-2.13.0/lib/python3.11/site-packages (2.13.0)
Requirement already satisfied: PyYAML in ./scuba-2.13.0/lib/python3.11/site-packages (from scuba==2.13.0) (6.0.1)
scuba 2.13.0
abcd
yes: standard output: Broken pipe

This matches the problem described above.

As does this:

$ strace -o yes.strace yes | echo abcd

yes.strace:

...
write(1, "y\ny\ny\ny\ny\ny\ny\ny\ny\ny\ny\ny\ny\ny\ny\ny\n"..., 8192) = -1 EPIPE (Broken pipe)
--- SIGPIPE {si_signo=SIGPIPE, si_code=SI_USER, si_pid=693228, si_uid=1000} ---
+++ killed by SIGPIPE +++