From d257044298f803d943bd0a4099b3c89db1e3a9ac Mon Sep 17 00:00:00 2001
From: Evgenii Stratonikov <evgeniy@nspcc.ru>
Date: Thu, 12 Sep 2019 10:39:54 +0300
Subject: [PATCH] vm: fail if XTUCK argument is 0

---
 pkg/vm/vm.go      | 2 +-
 pkg/vm/vm_test.go | 9 +++++++++
 2 files changed, 10 insertions(+), 1 deletion(-)

diff --git a/pkg/vm/vm.go b/pkg/vm/vm.go
index c9bc97d2b..db03e6deb 100644
--- a/pkg/vm/vm.go
+++ b/pkg/vm/vm.go
@@ -375,7 +375,7 @@ func (v *VM) execute(ctx *Context, op Instruction) {
 
 	case XTUCK:
 		n := int(v.estack.Pop().BigInt().Int64())
-		if n < 0 {
+		if n <= 0 {
 			panic("XTUCK: invalid length")
 		}
 		a := v.estack.Dup(0)
diff --git a/pkg/vm/vm_test.go b/pkg/vm/vm_test.go
index 5a7f5771a..a0682c1ab 100644
--- a/pkg/vm/vm_test.go
+++ b/pkg/vm/vm_test.go
@@ -658,6 +658,15 @@ func TestXTUCKbadNegative(t *testing.T) {
 	assert.Equal(t, true, vm.state.HasFlag(faultState))
 }
 
+func TestXTUCKbadZero(t *testing.T) {
+	prog := makeProgram(XTUCK)
+	vm := load(prog)
+	vm.estack.PushVal(1)
+	vm.estack.PushVal(0)
+	vm.Run()
+	assert.Equal(t, true, vm.state.HasFlag(faultState))
+}
+
 func TestXTUCKgood(t *testing.T) {
 	prog := makeProgram(XTUCK)
 	topelement := 5