kern_jail_set(): do not double-free opts

[kib]

Summary

If vfs_buildopts() failed, vfs_freeopts() must not be called.

Reported and tested by: pho

[jamie]

While I prefer the version I mentioned in the inline notes (it's a little less branchy), I'm also fine with the patch as originally given.

sys/kern/kern_jail.c

1046

This hold is the only reason that vfs_buildopts goes to done_free and doesn't just return outright...

1072

...so we could change the "goto done_free" above to "return (error)", and move "prison_hold(mypr)" here, just before the first of the remaining "goto done" lines...

2336–2337

...and then we wouldn't need to add this test.

[kib]

In D53612#1224147, @jamie wrote:

While I prefer the version I mentioned in the inline notes (it's a little less branchy), I'm also fine with the patch as originally given.

I did not wanted to restructure the main flow. If you consider it is worth to, please do as follow-up.