Bug#1056385: in unshare mode, ischroot returns false

[Jochen Sprickerhof]

* Johannes Schauer Marin Rodrigues <jo...@debian.org> [2023-11-24 20:57]:

this is is only invoked for --chrooted-*-hooks but CLONE_NEWNS is also what
mmdebstrap unshares by default here:

Ah, I only tested with your:

--chroot-setup-commands='ischroot && echo "is chroot" || echo "is not chroot"

Example.

This is already done here:

https://sources.debian.org/src/sbuild/0.85.4/lib/Sbuild/ChrootUnshare.pm/#L279

What made you think that CLONE_NEWNS was responsible? It should be unshared for
both sbuild and mmdebstrap hooks.

I think it is due to mmdebstrap having extra process and maybe doing the CLONE_NEWNS in a different process?

Since the problem does not happen with mmdebstrap, I think this might just be a
bug in sbuild. I also suspect that your thoughts about PID 1 go into the right
direction because sbuild and mmdebstrap set up the unshared processes slightly
differently. Look at the complex dance of processes that mmdebstrap does:

https://sources.debian.org/src/mmdebstrap/1.4.0-1/mmdebstrap/#L486

I think that is part of why it works with mmdebstrap. Compare:

$ sbuild -d unstable --starting-build-commands='ps auxf' --add-depends=procps 
hello
USER         PID %CPU %MEM    VSZ   RSS TTY      STAT START   TIME COMMAND
root           1  0.0  0.0   4536  2816 ?        S+   20:17   0:00 /sbin/runuser -u root -- sh -c cd "$1" 
&& shift && "$@" -- /build/package /bin/sh -c ps auxf
root          41  0.0  0.0   2580  1408 ?        S+   20:17   0:00 sh -c cd "$1" && shift 
&& "$@" -- /build/package /bin/sh -c ps auxf
root          42  0.0  0.0   2580  1408 ?        S+   20:17   0:00  \_ /bin/sh 
-c ps auxf
root          43  0.0  0.0   8116  4096 ?        R+   20:17   0:00      \_ ps 
auxf

and:

$ mmdebstrap --chrooted-customize-hook='ps auxf' --variant=essential 
--include=procps unstable /dev/null
USER         PID %CPU %MEM    VSZ   RSS TTY      STAT START   TIME COMMAND
root           1  0.5  0.1  32616 25252 ?        S+   20:15   0:00 
/usr/bin/perl /usr/bin/mmdebstrap --chrooted-customize-hook=ps auxf 
--variant=essential --include=procps unstable /dev/null
root        1716  0.0  0.1  32616 23956 ?        S+   20:15   0:00 
/usr/bin/perl /usr/bin/mmdebstrap --chrooted-customize-hook=ps auxf 
--variant=essential --include=procps unstable /dev/null
root        1717  0.0  0.0   2580  1536 ?        S+   20:15   0:00  \_ sh -c ps 
auxf
root        1718  0.0  0.0   8116  3968 ?        R+   20:15   0:00      \_ ps 
auxf



Cheers Jochen

And note that for mmdebstrap PID 1 has a different mountinfo as PID 1716 and below.

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