From 80143607f06fd6410700e9764cfea9aaac9c311c Mon Sep 17 00:00:00 2001
From: "Jason A. Donenfeld" <Jason@zx2c4.com>
Date: Tue, 24 Sep 2024 03:06:38 +0200
Subject: [PATCH] internal/syscall/unix: allow calling getrandom(..., 0, ...)

Calling getrandom() with a zero length is actually valid and useful:

- Calling getrandom(..., 0, 0) will block until the RNG is initialized.
- Calling getrandom(..., 0, GRND_NONBLOCK) will query whether the RNG
  is initialized.

So instead of short circuiting execution for these circumstances, pass
this through to the syscall.

Change-Id: I15178f087908a2d8be6c020a1ef800cc0a074742
Reviewed-on: https://go-review.googlesource.com/c/go/+/615315
Run-TryBot: Jason Donenfeld <Jason@zx2c4.com>
Reviewed-by: Filippo Valsorda <filippo@golang.org>
Auto-Submit: Jason Donenfeld <Jason@zx2c4.com>
Reviewed-by: Michael Pratt <mpratt@google.com>
Reviewed-by: Cuong Manh Le <cuong.manhle.vn@gmail.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Michael Knyszek <mknyszek@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
---
 src/internal/syscall/unix/getrandom.go | 5 +----
 1 file changed, 1 insertion(+), 4 deletions(-)

diff --git a/src/internal/syscall/unix/getrandom.go b/src/internal/syscall/unix/getrandom.go
index e83f0cd6f9..4270898b7e 100644
--- a/src/internal/syscall/unix/getrandom.go
+++ b/src/internal/syscall/unix/getrandom.go
@@ -19,14 +19,11 @@ type GetRandomFlag uintptr
 
 // GetRandom calls the getrandom system call.
 func GetRandom(p []byte, flags GetRandomFlag) (n int, err error) {
-	if len(p) == 0 {
-		return 0, nil
-	}
 	if getrandomUnsupported.Load() {
 		return 0, syscall.ENOSYS
 	}
 	r1, _, errno := syscall.Syscall(getrandomTrap,
-		uintptr(unsafe.Pointer(&p[0])),
+		uintptr(unsafe.Pointer(unsafe.SliceData(p))),
 		uintptr(len(p)),
 		uintptr(flags))
 	if errno != 0 {