Bug#1053470: ld.so: ignore tunables in secure mode

[Christian Göttsche <cgzones@googlemail.com>]

Package: glibc
Version: 2.37-12

In the light of the recent privilege escalation vulnerability I'd like
to suggest disabling the support for tunables in secure mode (most
notably for setuid-binaries).
This would mitigate future regressions in the handling of the
environment variable and possible vulnerabilities caused by the
interaction of particular options with security relevant applications.

The support could either be disabled at compile time[1] or at runtime
via a file existence check (either by reusing `/etc/suid-debug` or a
new one like `/etc/suid-tunables`).


[1]: https://git.altlinux.org/gears/g/glibc.git?p=glibc.git;a=commitdiff;h=5d1686416ab766f3dd0780ab730650c4c0f76ca9