Bug#992781: supermin: stores wrong path to chpasswd, etc. if built on merged-/usr system

[Simon McVittie]

Source: supermin
Version: 5.2.1-4
Severity: important
Tags: patch bookworm sid
User: reproducible-builds at lists.alioth.debian.org
Usertags: usrmerge
X-Debbugs-Cc: reproducible-bugs at lists.alioth.debian.org

If supermin is built on a merged-/usr system (as created by new
installations of Debian >= 10, debootstrap --merged-usr, or installing
the usrmerge package into an existing installation), the paths to
cpio, mke2fs, zcat are recorded in the binary as /usr/bin/cpio,
/usr/sbin/mke2fs, /usr/bin/zcat rather than their canonical paths in
/bin and /sbin.

This can be seen on the reproducible-builds.org infra:
https://tests.reproducible-builds.org/debian/rb-pkg/unstable/amd64/diffoscope-results/supermin.html

If you have sbuild available, an easy way to reproduce this is to build
twice, once with --add-depends-arch=usrmerge and once without.

I suspect the same thing would happen if supermin was built on a system
where /bin and /usr/bin had instead been unified via a symlink farm.

The problematic situation is if the package is *built* on a unified-/usr
system, but *used* on a non-unified-/usr system. In this situation,
/usr/bin/cpio etc. exist on the build system but not on the system
where supermin will be used, resulting in the features that use these
executables not being available.

Technical Committee resolution #978636 mandates heading towards a
transition to merged-/usr, and this will become a non-issue at the end of
that transition; but variation between merged-/usr and non-merged-/usr
builds is a problem while that transition is taking place, because it
can lead to partial upgrades behaving incorrectly. It is likely that
this class of bugs will become release-critical later in the bookworm
development cycle.

The attached patch resolves this: with it applied, the package builds
identically with and without --add-depends-arch=usrmerge.

Some developers advocate unifying /bin with /usr/bin via a symlink farm
in /bin instead of merged-/usr, but that strategy would have a similar
practical effect on this particular package, and the same solution would
be required.

A side benefit of fixing this is that this change seems likely to be
sufficient to make the package reproducible (as recommended by Policy
§4.15).

    smcv
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