Add mmap protected buffer to verify under/over flows (#34)

* add mmap protected buffer to verify under/over flows

* remove unused fill functions

Author: kalamay

ascii/ascii_test.go

@@ -6,6 +6,8 @@ import (
 	"strings"
 	"testing"
 	"unicode/utf8"
+
+	"github.com/segmentio/asm/internal/buffer"
 )
 
 var testStrings = [...]string{
@@ -65,45 +67,49 @@ func testValidPrint(s string) bool {
 }
 
 func TestValid(t *testing.T) {
-	var input [1024]byte
-
-	for i := 0; i < len(input); i++ {
-		in := input[:i+1]
-
-		for b := 0; b <= 0xFF; b++ {
-			in[i] = byte(b)
-			if b < 0x80 {
-				if !Valid(in) {
-					t.Errorf("should be valid: %v", in)
-				}
-			} else {
-				if Valid(in) {
-					t.Errorf("should not be valid: %v", in)
+	buf := newBuffer(t, 1024)
+
+	for _, input := range [2][]byte{buf.ProtectHead(), buf.ProtectTail()} {
+		for i := 0; i < len(input); i++ {
+			in := input[:i+1]
+
+			for b := 0; b <= 0xFF; b++ {
+				in[i] = byte(b)
+				if b < 0x80 {
+					if !Valid(in) {
+						t.Errorf("should be valid: %v", in)
+					}
+				} else {
+					if Valid(in) {
+						t.Errorf("should not be valid: %v", in)
+					}
 				}
+				in[i] = 'x'
 			}
-			in[i] = 'x'
 		}
 	}
 }
 
 func TestValidPrint(t *testing.T) {
-	var input [1024]byte
-
-	for i := 0; i < len(input); i++ {
-		in := input[:i+1]
-
-		for b := 0; b <= 0xFF; b++ {
-			in[i] = byte(b)
-			if ' ' <= b && b <= '~' {
-				if !ValidPrint(in) {
-					t.Errorf("should be valid: %v", in)
-				}
-			} else {
-				if ValidPrint(in) {
-					t.Errorf("should not be valid: %v", in)
+	buf := newBuffer(t, 1024)
+
+	for _, input := range [2][]byte{buf.ProtectHead(), buf.ProtectTail()} {
+		for i := 0; i < len(input); i++ {
+			in := input[:i+1]
+
+			for b := 0; b <= 0xFF; b++ {
+				in[i] = byte(b)
+				if ' ' <= b && b <= '~' {
+					if !ValidPrint(in) {
+						t.Errorf("should be valid: %v", in)
+					}
+				} else {
+					if ValidPrint(in) {
+						t.Errorf("should not be valid: %v", in)
+					}
 				}
+				in[i] = 'x'
 			}
-			in[i] = 'x'
 		}
 	}
 }
@@ -232,8 +238,27 @@ func TestEqualFoldString(t *testing.T) {
 	}
 }
 
+func newBuffer(t *testing.T, n int) buffer.Buffer {
+	buf, err := buffer.New(n)
+	if err != nil {
+		t.Fatal(err)
+	}
+	return buf
+}
+
 func TestEqualFold(t *testing.T) {
-	var upper, lower, mixed [1024]byte
+	ubuf := newBuffer(t, 1024)
+	defer ubuf.Release()
+
+	lbuf := newBuffer(t, 1024)
+	defer lbuf.Release()
+
+	mbuf := newBuffer(t, 1024)
+	defer mbuf.Release()
+
+	upper := ubuf.ProtectHead()
+	lower := lbuf.ProtectTail()
+	mixed := mbuf.ProtectHead()
 
 	for i := 0; i < len(upper); i++ {
 		u := upper[:i+1]

internal/buffer/buffer_default.go

@@ -0,0 +1,20 @@
+// +build !aix,!android,!darwin,!dragonfly,!freebsd,!illumos,!ios,!linux,!netbsd,!openbsd,!plan9,!solaris
+
+package buffer
+
+type Buffer []byte
+
+func New(n int) (Buffer, error) {
+	return make([]byte, n), nil
+}
+
+func (a *Buffer) ProtectHead() []byte {
+	return []byte(*a)
+}
+
+func (a *Buffer) ProtectTail() []byte {
+	return []byte(*a)
+}
+
+func (a *Buffer) Release() {
+}

internal/buffer/buffer_mmap.go

@@ -0,0 +1,51 @@
+// +build aix android darwin dragonfly freebsd illumos ios linux netbsd openbsd plan9 solaris
+
+package buffer
+
+import (
+	"syscall"
+)
+
+type Buffer struct {
+	n    int
+	pg   int
+	mmap []byte
+}
+
+func New(n int) (Buffer, error) {
+	pg := syscall.Getpagesize()
+	full := ((n+(pg-1))/pg + 2) * pg
+
+	b, err := syscall.Mmap(-1, 0, full, syscall.PROT_NONE, syscall.MAP_ANON|syscall.MAP_PRIVATE)
+	if err != nil {
+		return Buffer{}, err
+	}
+
+	if n > 0 {
+		err = syscall.Mprotect(b[pg:full-pg], syscall.PROT_READ|syscall.PROT_WRITE)
+		if err != nil {
+			syscall.Munmap(b)
+			return Buffer{}, err
+		}
+	}
+
+	return Buffer{
+		n:    n,
+		pg:   pg,
+		mmap: b,
+	}, nil
+}
+
+func (a *Buffer) ProtectHead() []byte {
+	head := a.pg
+	return a.mmap[head : head+a.n]
+}
+
+func (a *Buffer) ProtectTail() []byte {
+	tail := len(a.mmap) - a.pg - a.n
+	return a.mmap[tail : tail+a.n]
+}
+
+func (a *Buffer) Release() {
+	syscall.Munmap(a.mmap)
+}