modstat: don't copyout while holding a lock

[brooks]

Summary

If a user arranges for a page fault to never be filled (e.g., via a
FUSE file system), this can hold the shared lock forever.

To make this all work, refactor kern_modstat and freebsd32_modstat to
malloc a temporary buffer and fill it before copying it out rather
than doing a bunch of copies.

Add COMPAT_* ifdefs around compat code. The module_stat_v1 code is
really for a.out binaries in practice and thus a bit questionable.

Reported by: llm-postcr
Sponsored by: Innovate UK
Fixes: 7f8c2056db1e ("modstat: avoid copying from freed memory")

[brooks]

The second LLM review convinced me to fix this more properly.

I think we could go one step further and add the compat bits to kern_modstat with freebsd32_modstat being a trivial wrapper, but I've left them split for now.

[markj]

sys/kern/kern_module.c

632

This unlock needs to be removed, and statbuf needs to be freed here like in the native implementation.

[brooks]

Thanks for the review. That error I made probably argues for further consolidation, but I'll hold off for the moment.

[brooks]

freebsd32_modstat: Don't unlock twice, do free statbuf