sysctl: Add a regression test which runs sysctl -a

[markj]

Summary

Run sysctl -a during the test suite so that KASAN/KMSAN have a chance to
catch something.

Inspired by https://jprx.io/cve-2024-54507/

[markj]

Go a bit further: add a test which does the same thing in a jail.

[emaste]

sbin/sysctl/tests/sysctl_test.sh

36

I'm not sure if "Verify" is correct here as we don't actually care about the results. Something like "Exercise kernel code via -a" or so? And a comment referencing KASAN/KMSAN.

[markj]

Improve test descriptions.

[brooks]

I wonder if you want to run with -x -a as well or instead?

[emaste]

-x sounds good too

[markj]

Add -x to the sysctl flags

[markj]

• Use -o instead of -x: with the latter sysctl(8) will print a huge amount of output and is a couple orders of magnitude slower. We get the same kernel coverage with -o, so just use that.
• Avoid using atf_check: it causes kyua to buffer all of the output in memory and then store it in the test results DB, which is somewhat unwieldy. Check the exit status manually.

[emaste]

does sysctl -o still pass all the data to userspace but then only print the first bit?

[markj]

In D48659#1110770, @emaste wrote:

does sysctl -o still pass all the data to userspace but then only print the first bit?

Yeah, the only difference is in how sysctl(8) formats and outputs the data.