1 files changed, 87 insertions, 0 deletions
diff --git a/src/crypto/rand/rand_unix.go b/src/crypto/rand/rand_unix.go
new file mode 100644
index 0000000..40fce36
--- /dev/null
+++ b/src/crypto/rand/rand_unix.go
@@ -0,0 +1,87 @@
+// Copyright 2010 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+//go:build unix
+
+// Unix cryptographically secure pseudorandom number
+// generator.
+
+package rand
+
+import (
+	"crypto/internal/boring"
+	"errors"
+	"io"
+	"os"
+	"sync"
+	"sync/atomic"
+	"syscall"
+	"time"
+)
+
+const urandomDevice = "/dev/urandom"
+
+func init() {
+	if boring.Enabled {
+		Reader = boring.RandReader
+		return
+	}
+	Reader = &reader{}
+}
+
+// A reader satisfies reads by reading from urandomDevice
+type reader struct {
+	f    io.Reader
+	mu   sync.Mutex
+	used atomic.Uint32 // Atomic: 0 - never used, 1 - used, but f == nil, 2 - used, and f != nil
+}
+
+// altGetRandom if non-nil specifies an OS-specific function to get
+// urandom-style randomness.
+var altGetRandom func([]byte) (err error)
+
+func warnBlocked() {
+	println("crypto/rand: blocked for 60 seconds waiting to read random data from the kernel")
+}
+
+func (r *reader) Read(b []byte) (n int, err error) {
+	boring.Unreachable()
+	if r.used.CompareAndSwap(0, 1) {
+		// First use of randomness. Start timer to warn about
+		// being blocked on entropy not being available.
+		t := time.AfterFunc(time.Minute, warnBlocked)
+		defer t.Stop()
+	}
+	if altGetRandom != nil && altGetRandom(b) == nil {
+		return len(b), nil
+	}
+	if r.used.Load() != 2 {
+		r.mu.Lock()
+		if r.used.Load() != 2 {
+			f, err := os.Open(urandomDevice)
+			if err != nil {
+				r.mu.Unlock()
+				return 0, err
+			}
+			r.f = hideAgainReader{f}
+			r.used.Store(2)
+		}
+		r.mu.Unlock()
+	}
+	return io.ReadFull(r.f, b)
+}
+
+// hideAgainReader masks EAGAIN reads from /dev/urandom.
+// See golang.org/issue/9205
+type hideAgainReader struct {
+	r io.Reader
+}
+
+func (hr hideAgainReader) Read(p []byte) (n int, err error) {
+	n, err = hr.r.Read(p)
+	if errors.Is(err, syscall.EAGAIN) {
+		err = nil
+	}
+	return
+}