Re: Bug in interaction with pid namespaces

[Bart Schaefer <schaefer@brasslantern.com>]

On Dec 16, 11:50pm, Chirantan Ekbote wrote:
}
} We're not trying to use zsh as a replacement for init. I first noticed
} this issue because the chrome os build system recently switched to
} using pid namespaces in the build chroot. [...] In the actual workflow
} where this is an issue for me, the pid is somewhere in the 240 to 270
} range and zsh is only meant to behave like a regular shell.

OK, so the issue is that zsh is started as a (possibly indirect) child
of whatever was given "leadership" of the namespace, but at the time
zsh starts GETPGRP() == 0.

That sounds like a bug in one of the ancestor processes, then, because
shouldn't whatever *that* is, have become a group leader, or assigned
the process group to the fork() pid before execve() of zsh?

} > } -    if ((mypgrp = GETPGRP()) > 0) {
} > } +    if ((mypgrp = GETPGRP()) >= 0) {
} >
} > I don't see any reason not to make that change ...
} >
} 
} Excellent.  Should I re-send it as a proper patch?

No need, I already applied it and pushed it to the repository.

} So the problem is that on exit zsh gives a warning:
} 
}     zsh: can't set tty pgrp: no such process
} 
} which I thought was due to the call to setpgrp() but is actually in
} the call to attachtty().

Aha.  That means that one of

	tcsetpgrp(SHTTY, pgrp)
or
	arg = &pgrp
	ioctl(SHTTY, TIOCSPGRP, &arg)

is returning -1 and errno == ESRCH.  Which makes sense if pgrp == 0.

But that also means that zsh is being invoked as an interactive shell,
because attachtty() is a no-op otherwise.  I can't imagine why the
chrome os build would need to run an interactive shell.

However, I suggest the following.  The mypgrp = origpgrp assignment is
questionable because the pgrp won't actually have been changed, but it
may help elsewhere in tests that mypgrp != GETPGRP().  Shell exit is
not the only place where release_pgrp() is called.

diff --git a/Src/jobs.c b/Src/jobs.c
index 8c4254a..c6e1bce 100644
--- a/Src/jobs.c
+++ b/Src/jobs.c
@@ -2779,8 +2779,11 @@ void
 release_pgrp(void)
 {
     if (origpgrp != mypgrp) {
-	attachtty(origpgrp);
-	setpgrp(0, origpgrp);
+	/* in linux pid namespaces, origpgrp may never have been set */
+	if (origpgrp) {
+	    attachtty(origpgrp);
+	    setpgrp(0, origpgrp);
+	}
 	mypgrp = origpgrp;
     }
 }