Merge pull request #461 from nspcc-dev/feature/stack_limits

vm: restrict max invocation stack size

pkg/vm/vm.go

@@ -41,6 +41,9 @@ const (
 	// MaxItemSize is the maximum item size allowed in the VM.
 	MaxItemSize = 1024 * 1024
 
+	// MaxInvocationStackSize is the maximum size of an invocation stack.
+	MaxInvocationStackSize = 1024
+
 	maxSHLArg = 256
 	minSHLArg = -256
 )
@@ -995,6 +998,8 @@ func (v *VM) execute(ctx *Context, op Instruction, parameter []byte) (err error)
 		}
 
 	case CALL:
+		v.checkInvocationStackSize()
+
 		newCtx := ctx.Copy()
 		newCtx.rvcount = -1
 		v.istack.PushVal(newCtx)
@@ -1017,6 +1022,10 @@ func (v *VM) execute(ctx *Context, op Instruction, parameter []byte) (err error)
 			panic("no getScript callback is set up")
 		}
 
+		if op == APPCALL {
+			v.checkInvocationStackSize()
+		}
+
 		hash, err := util.Uint160DecodeBytes(parameter)
 		if err != nil {
 			panic(err)
@@ -1227,9 +1236,13 @@ func (v *VM) execute(ctx *Context, op Instruction, parameter []byte) (err error)
 		if v.estack.Len() < pcount+addElement {
 			panic("missing some parameters")
 		}
-		if tailCall && ctx.rvcount != rvcount {
+		if tailCall {
+			if ctx.rvcount != rvcount {
 				panic("context and parameter rvcount mismatch")
 			}
+		} else {
+			v.checkInvocationStackSize()
+		}
 
 		if op == CALLI {
 			newCtx = ctx.Copy()
@@ -1313,3 +1326,9 @@ func validateMapKey(key *Element) {
 		panic("key can't be a collection")
 	}
 }
+
+func (v *VM) checkInvocationStackSize() {
+	if v.istack.len >= MaxInvocationStackSize {
+		panic("invocation stack is too big")
+	}
+}

pkg/vm/vm_test.go

@@ -197,6 +197,27 @@ func TestPushData4Good(t *testing.T) {
 	assert.Equal(t, []byte{1, 2, 3}, vm.estack.Pop().Bytes())
 }
 
+func callNTimes(n uint16) []byte {
+	return makeProgram(
+		PUSHBYTES2, Instruction(n), Instruction(n>>8), // little-endian
+		TOALTSTACK, DUPFROMALTSTACK,
+		JMPIF, 0x4, 0, RET,
+		FROMALTSTACK, DEC,
+		CALL, 0xF8, 0xFF) // -8 -> JMP to TOALTSTACK)
+}
+
+func TestInvocationLimitGood(t *testing.T) {
+	prog := callNTimes(MaxInvocationStackSize - 1)
+	v := load(prog)
+	runVM(t, v)
+}
+
+func TestInvocationLimitBad(t *testing.T) {
+	prog := callNTimes(MaxInvocationStackSize)
+	v := load(prog)
+	checkVMFailed(t, v)
+}
+
 func TestNOTNoArgument(t *testing.T) {
 	prog := makeProgram(NOT)
 	vm := load(prog)