flag: validate Int and Uint values to be in range

Fixes #19230

Change-Id: I38df9732b88f0328506e74f1a46f52adf47db1e5
Reviewed-on: https://go-review.googlesource.com/38419
Reviewed-by: Robert Griesemer <gri@golang.org>
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>

src/flag/flag.go

@@ -114,7 +114,7 @@ func newIntValue(val int, p *int) *intValue {
 }
 
 func (i *intValue) Set(s string) error {
-	v, err := strconv.ParseInt(s, 0, 64)
+	v, err := strconv.ParseInt(s, 0, strconv.IntSize)
 	*i = intValue(v)
 	return err
 }
@@ -150,7 +150,7 @@ func newUintValue(val uint, p *uint) *uintValue {
 }
 
 func (i *uintValue) Set(s string) error {
-	v, err := strconv.ParseUint(s, 0, 64)
+	v, err := strconv.ParseUint(s, 0, strconv.IntSize)
 	*i = uintValue(v)
 	return err
 }

src/flag/flag_test.go

@@ -10,6 +10,7 @@ import (
 	"fmt"
 	"os"
 	"sort"
+	"strconv"
 	"strings"
 	"testing"
 	"time"
@@ -415,3 +416,19 @@ func TestPrintDefaults(t *testing.T) {
 		t.Errorf("got %q want %q\n", got, defaultOutput)
 	}
 }
+
+// Issue 19230: validate range of Int and Uint flag values.
+func TestIntFlagOverflow(t *testing.T) {
+	if strconv.IntSize != 32 {
+		return
+	}
+	ResetForTesting(nil)
+	Int("i", 0, "")
+	Uint("u", 0, "")
+	if err := Set("i", "2147483648"); err == nil {
+		t.Error("unexpected success setting Int")
+	}
+	if err := Set("u", "4294967296"); err == nil {
+		t.Error("unexpected success setting Uint")
+	}
+}