[release-branch.go1.17] crypto/rand: properly handle large Read on windows

Use the batched reader to chunk large Read calls on windows to a max of
1 << 31 - 1 bytes. This prevents an infinite loop when trying to read
more than 1 << 32 -1 bytes, due to how RtlGenRandom works.

This change moves the batched function from rand_unix.go to rand.go,
since it is now needed for both windows and unix implementations.

Updates #52561
Fixes #52932
Fixes CVE-2022-30634

Change-Id: Id98fc4b1427e5cb2132762a445b2aed646a37473
Reviewed-on: https://go-review.googlesource.com/c/go/+/402257
Run-TryBot: Roland Shoemaker <roland@golang.org>
Reviewed-by: Filippo Valsorda <filippo@golang.org>
Reviewed-by: Filippo Valsorda <valsorda@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
(cherry picked from commit bb1f4416180511231de6d17a1f2f55c82aafc863)
Reviewed-on: https://go-review.googlesource.com/c/go/+/406635
Reviewed-by: Damien Neil <dneil@google.com>

1 files changed, 3 insertions, 3 deletions

diff --git a/src/crypto/rand/rand_getentropy.go b/src/crypto/rand/rand_getentropy.go
index dd725372ad..b1c19f3d0d 100644
--- a/src/crypto/rand/rand_getentropy.go
+++ b/src/crypto/rand/rand_getentropy.go
@@ -15,7 +15,7 @@ func init() {
 	altGetRandom = getEntropy
 }
 
-func getEntropy(p []byte) (ok bool) {
+func getEntropy(p []byte) error {
 	// getentropy(2) returns a maximum of 256 bytes per call
 	for i := 0; i < len(p); i += 256 {
 		end := i + 256
@@ -24,8 +24,8 @@ func getEntropy(p []byte) (ok bool) {
 		}
 		err := unix.GetEntropy(p[i:end])
 		if err != nil {
-			return false
+			return err
 		}
 	}
-	return true
+	return nil
 }