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crypto/internal/rand: avoid MaybeReadByte non-determinism with SetGlobalRandom

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Change-Id: I2dc3b7d116c4750153a324ee9850ca576a6a6964
Reviewed-on: https://go-review.googlesource.com/c/go/+/765921
Reviewed-by: Daniel McCarney <daniel@binaryparadox.net>
Reviewed-by: Mark Freeman <markfreeman@google.com>
Auto-Submit: Filippo Valsorda <filippo@golang.org>
LUCI-TryBot-Result: golang-scoped@luci-project-accounts.iam.gserviceaccount.com <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: David Chase <drchase@google.com>
This commit is contained in:
Filippo Valsorda 2026-04-06 16:40:34 +02:00 • committed by Gopher Robot
parent da36c0eecd
commit 58968c79e7
1 changed files with 8 additions and 2 deletions
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10
src/crypto/internal/rand/rand.go
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@ -46,19 +46,25 @@ var Reader io.Reader = reader{}
//
//go:linkname SetTestingReader crypto/internal/rand.SetTestingReader
func SetTestingReader(r io.Reader) {
testingReader = r
fips140SetTestingReader(r)
}
var testingReader io.Reader
var cryptocustomrand = godebug.New("cryptocustomrand")
// CustomReader returns [Reader] or, only if the GODEBUG setting
// "cryptocustomrand=1" is set, the provided io.Reader.
//
// If returning a non-default Reader, it calls [randutil.MaybeReadByte] on it.
// If returning a non-default Reader, it calls [randutil.MaybeReadByte] on it,
// unless it's the global testing Reader set with [SetTestingReader].
func CustomReader(r io.Reader) io.Reader {
if cryptocustomrand.Value() == "1" {
if !IsDefaultReader(r) {
randutil.MaybeReadByte(r)
if r != testingReader {
randutil.MaybeReadByte(r)
}
cryptocustomrand.IncNonDefault()
}
return r