Merge pull request #435 from nspcc-dev/fix/max_item_size

Restrict max item size on stack in CAT and PUSHDATA4, one more step towards #373.

pkg/vm/context.go

@@ -59,6 +59,9 @@ func (c *Context) Next() (Instruction, []byte, error) {
 	case PUSHDATA4:
 		var n uint32
 		r.ReadLE(&n)
+		if n > MaxItemSize {
+			return instr, nil, errors.New("parameter is too big")
+		}
 		numtoread = int(n)
 		c.nextip += 4
 	case JMP, JMPIF, JMPIFNOT, CALL:

pkg/vm/vm.go

@@ -28,8 +28,12 @@ var (
 const (
 	// MaxArraySize is the maximum array size allowed in the VM.
 	MaxArraySize = 1024
-	maxSHLArg    = 256
+
-	minSHLArg    = -256
+	// MaxItemSize is the maximum item size allowed in the VM.
+	MaxItemSize = 1024 * 1024
+
+	maxSHLArg = 256
+	minSHLArg = -256
 )
 
 // VM represents the virtual machine.
@@ -439,6 +443,9 @@ func (v *VM) execute(ctx *Context, op Instruction, parameter []byte) {
 	case CAT:
 		b := v.estack.Pop().Bytes()
 		a := v.estack.Pop().Bytes()
+		if l := len(a) + len(b); l > MaxItemSize {
+			panic(fmt.Sprintf("too big item: %d", l))
+		}
 		ab := append(a, b...)
 		v.estack.PushVal(ab)
 	case SUBSTR:

pkg/vm/vm_test.go

@@ -2,6 +2,7 @@ package vm
 
 import (
 	"bytes"
+	"encoding/binary"
 	"encoding/hex"
 	"math/big"
 	"math/rand"
@@ -175,6 +176,16 @@ func TestPushData4ShortN(t *testing.T) {
 	assert.Equal(t, true, vm.HasFailed())
 }
 
+func TestPushData4BigN(t *testing.T) {
+	prog := make([]byte, 1+4+MaxItemSize+1)
+	prog[0] = byte(PUSHDATA4)
+	binary.LittleEndian.PutUint32(prog[1:], MaxItemSize+1)
+
+	vm := load(prog)
+	vm.Run()
+	assert.Equal(t, true, vm.HasFailed())
+}
+
 func TestPushData4Good(t *testing.T) {
 	prog := makeProgram(PUSHDATA4, 3, 0, 0, 0, 1, 2, 3)
 	vm := load(prog)
@@ -1413,6 +1424,15 @@ func TestCATBadOneArg(t *testing.T) {
 	assert.Equal(t, true, vm.HasFailed())
 }
 
+func TestCATBadBigItem(t *testing.T) {
+	prog := makeProgram(CAT)
+	vm := load(prog)
+	vm.estack.PushVal(make([]byte, MaxItemSize/2+1))
+	vm.estack.PushVal(make([]byte, MaxItemSize/2+1))
+	vm.Run()
+	assert.Equal(t, true, vm.HasFailed())
+}
+
 func TestCATGood(t *testing.T) {
 	prog := makeProgram(CAT)
 	vm := load(prog)