How many times do you see a bug investigation and it's determined when the bug was introduced?
Do you ever look at the diff that introduced it to understand what was going on in the project at the time? Often, it's in service to a new feature. Sometimes the original change is questionable when you consider you traded it for a severe bug.
Yes necessarily. Always. You need to invoke Nasa and fighter jets to find anything coming close, and they only manage to do any better by massive brute overkill in standards & procedures.
Linux is a much larger project receiving changes to tons of systems from lots of different sources. The combined behaviour of those things working together is massively harder to understand and test.
Copyfail being introduced by an optimization made to some random crypto module is a good example of this.
The others and I, working on GNU coreutils, frequently use 'yes' to generate a bunch of garbage input for testing programs. It is nice that it can do so quickly.
Just as another point of comparison, FreeBSD's version seems somewhere in-between. It also enables a Capsicum sandbox before processing any data, akin to what the OpenBSD version does with pledge.
Difference is that capsicum is after the fact and mostly about file descriptors. You need to open them in advance and _then_ call capsicum. But it does nothing about syscalls.
Capsicum is really nice if you plan ahead, but pledge/unveil is easy to drop into any existing code base.