route: avoid overlapping strcpy(3)

[kevans]

Summary

strcpy(3) does not guarantee any particular outcome for aliasing
violations in dst/src. Furthermore, _FORTIFY_SOURCE will outright
abort. Switch to memmove(3) for an overlap-safe copy.

While we're here, improve the readability slightly by giving cp a
more sensible name, and using sizeof() for the gethostname(3) buffer
size to formalize our assumption that we still have room for us to
NUL-terminate the buffer to be safe.

Sponsored by: Klara, Inc.
Sponsored by: Stormshield

[kevans]

In trying to figure out why I hadn't found this in my smoke-tests, I discovered I had fixed this in another branch from when I initially did the work. Attaching the alternate version, I'm not sure which I prefer; that one just avoids copying by making domain a pointer into domain-renamed-to-domain_storage.

{F89079343}

[kevans]

And an accompanying review: D32615

[fuz]

Wouldn't it be much simpler to just keep a pointer to the domain part around rather than moving it to the beginning of the domain array?

[allanjude]

In D46069#1050289, @fuz wrote:

Wouldn't it be much simpler to just keep a pointer to the domain part around rather than moving it to the beginning of the domain array?

That seems to be what Kyle did here: https://reviews.freebsd.org/D32615

[emaste]

I prefer D32615

[kevans]

Consensus moves for the first attempt