[release-branch.go1] crypto/rand: zero length reads shouldn't crash on Windows.

««« backport a69e30463bf4
crypto/rand: zero length reads shouldn't crash on Windows.

R=golang-dev, dave
CC=golang-dev
https://golang.org/cl/6496099

»»»

2 files changed, 15 insertions, 0 deletions

diff --git a/src/pkg/crypto/rand/rand_test.go b/src/pkg/crypto/rand/rand_test.go
index be3a5a221d..c5dbdb6cb8 100644
--- a/src/pkg/crypto/rand/rand_test.go
+++ b/src/pkg/crypto/rand/rand_test.go
@@ -29,3 +29,14 @@ func TestRead(t *testing.T) {
 		t.Fatalf("Compressed %d -> %d", len(b), z.Len())
 	}
 }
+
+func TestReadEmpty(t *testing.T) {
+	n, err := Reader.Read(make([]byte, 0))
+	if n != 0 || err != nil {
+		t.Fatalf("Read(make([]byte, 0)) = %d, %v", n, err)
+	}
+	n, err = Reader.Read(nil)
+	if n != 0 || err != nil {
+		t.Fatalf("Read(make(nil) = %d, %v", n, err)
+	}
+}
diff --git a/src/pkg/crypto/rand/rand_windows.go b/src/pkg/crypto/rand/rand_windows.go
index 2b2bd4bba6..82b39b64a3 100644
--- a/src/pkg/crypto/rand/rand_windows.go
+++ b/src/pkg/crypto/rand/rand_windows.go
@@ -35,6 +35,10 @@ func (r *rngReader) Read(b []byte) (n int, err error) {
 		}
 	}
 	r.mu.Unlock()
+
+	if len(b) == 0 {
+		return 0, nil
+	}
 	err = syscall.CryptGenRandom(r.prov, uint32(len(b)), &b[0])
 	if err != nil {
 		return 0, os.NewSyscallError("CryptGenRandom", err)