confd: fix double free of container hostname

[rical]

Description

Fix a double free in the memory minefield surrounding container hostname provisioning. The hostnamefmt() function already does free() on success.

This caused all sorts of mayhem when working with multiple containers. However it mainly manifested itself by some containers not starting due to there activation script being polluted with gibberish name data. Your symptom might be different..

Example of polluted activation script

container --hostname foobar --net veth0k -r always \ create ^S@`M-}^G docker://ghcr.io/kernelkit/curios:edge

Side note

I haven't looked into it but is it really legit to free memory returned from the various lydx_ functions used here?
It seems to work as intended but it looks risky at a glance.

Checklist

Tick relevant boxes, this PR is-a or has-a:

• Bugfix
  • Regression tests
  • ChangeLog updates (for next release)
• Feature
  • YANG model change => revision updated?
  • Regression tests added?
  • ChangeLog updates (for next release)
  • Documentation added?
• Test changes
  • Checked in changed Readme.adoc (make test-spec)
  • Added new test to group Readme.adoc and yaml file
• Code style update (formatting, renaming)
• Refactoring (please detail in commit messages)
• Build related changes
• Documentation content changes
• Other (please describe):

[troglobit]

Ouch, nice catch! Although I cannot cannot reproduce in my limited setup, I agree that the current code needs work, and your fix is a good start, so let's merge this.

I'll submit a PR later that refactors int hostnamefmt(struct confd *confd, char **fmt) into int hostnamefmt(struct confd *confd, const char *fmt, char *buf, size_t len). Because we know that a hostname in Linux can only be 64 chars long, so a stack buffer for the return value is a much safer alternative.