pkg/rand: replace SafeRand by global source in math/rand

[tklauser]

Since Go 1.20 the top-level math/rand functions are auto-seeded by default, see https://go.dev/doc/go1.20#library and golang/go#54880. They also use the runtime's lock-free fastrand64 function when 1. Seed has not been called and 2. GODEBUG=randautoseed=0 is not used, see golang/go#49892.

This allows to drop SafeRand and use the global source again. SafeRand was originally introduced in commit fac5dde ("rand: add and use concurrency-safe PRNG source") to fix #10988 by providing a concurrency-safe PRNG source other than the global math/rand source which couldn't be used at the time because it can be interfered with from unrelated packages by means of calling rand.Seed, see #10575. rand.Seed is deprecated since Go 1.20 and per the paragraph above the global source is seeded by default. This makes it unlikely that packages would interfere with the global PRNG state anymore and the top-level math/rand functions are safe to use again.

[tklauser]

/test

[marseel]

1. Seed has not been called

If I understand correctly, how can we ensure that some packages we import don't call rand.Seed?
For example, here is one case:

cilium/vendor/github.com/servak/go-fastping/fastping.go

Line 157 in 8b31dff

rand.Seed(time.Now().UnixNano())

which we call from here

cilium/pkg/health/server/prober.go

Line 382 in 52c06e1

Pinger: fastping.NewPinger(),

[tklauser]

1. Seed has not been called

If I understand correctly, how can we ensure that some packages we import don't call rand.Seed? For example, here is one case:

Good point. I guess we could use some kind of checker akin to ./contrib/scripts/rand-check.sh and run it against vendored code as well and fix any occurrences upstream.

That doesn't sound like a really feasible approach though. I think instead we should wait for the math/rand/v2 package released in the upcoming Go 1.22 and switch to use that instead of pkg/rand. That package gets rid of the Seed method and global function altogether.

[github-actions]

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[tklauser]

Superseded by #32542