uucore: reject non-regular and oversized locale files

[mattsu2020]

Summary

Fix a localization startup issue where .ftl files were read with fs::read_to_string() without validating the target file type or size first.

If a locale file is symlinked to /dev/zero, startup can keep reading indefinitely until the process is killed by OOM. This affects utilities like true because localization is initialized before the utility runs.

What changed

• added a guarded locale file reader for .ftl files
• reject non-regular files before reading locale contents
• enforce a maximum locale file size to avoid unbounded reads
• route locale resource loading through the new safe reader

Tests

Added coverage for:

• rejecting a non-regular locale path
• rejecting an oversized locale file
• rejecting a locale symlink that points to /dev/zero
• still accepting a symlink that points to a regular locale file

Result

Utilities no longer risk unbounded memory growth during localization setup when locale files point to special files such as /dev/zero.

issue

#11230

[github-actions]

GNU testsuite comparison:

Skip an intermittent issue tests/cut/bounded-memory (fails in this run but passes in the 'main' branch)
Skip an intermittent issue tests/date/date-locale-hour (fails in this run but passes in the 'main' branch)
Skip an intermittent issue tests/date/resolution (fails in this run but passes in the 'main' branch)
Skip an intermittent issue tests/pr/bounded-memory (fails in this run but passes in the 'main' branch)
Skipping an intermittent issue tests/tail/follow-name (passes in this run but fails in the 'main' branch)
Note: The gnu test tests/env/env-signal-handler was skipped on 'main' but is now failing.

[sylvestre]

i found this overkill for something that will never happen in real life

[oech3]

How about loading *.ftl to stack with sizes determined at build.rs for perf?

[oech3]

This does not happen for proper packages. So I think we can just remove localization feature from https://github.com/uutils/coreutils/releases by --features feat_no_locales.