Bug#993675: opensmtpd: stores wrong path to zcat if /usr/bin/zcat or /usr/local/bin/zcat exists

[Simon McVittie]

Source: opensmtpd
Version: 6.8.0p2-3
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 opensmtpd 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 path to zcat
is recorded in the binary package as /usr/bin/zcat, rather than the
canonical /bin/zcat.

This can be seen on the reproducible-builds.org infra:
https://tests.reproducible-builds.org/debian/rb-pkg/unstable/i386/diffoscope-results/opensmtpd.html

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

I suspect the same thing would happen if opensmtpd was built on a system
where /sbin and /usr/sbin 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/zcat exists on the build system but not on the system where
the package will be used, resulting in the features that use this
executable not working correctly.

Similarly, if there is a /usr/local/bin/zcat visible at build-time,
then that path would likely end up hard-coded into the binary,
causing the relevant feature to fail on all systems that do not have
/usr/local/bin/zcat.

Technical Committee resolution #978636 mandates heading towards a
transition to merged-/usr, and 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=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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