vm: add some Fuzz tests

Both `IsScriptCorrect` and `VM.Run` should never panic.

Signed-off-by: Evgeniy Stratonikov <evgeniy@nspcc.ru>

.gitignore

@@ -42,3 +42,17 @@ coverage.html
 # Compiler output
 examples/*/*.nef
 examples/*/*.json
+
+# Fuzzing testdata.
+testdata/
+!cli/testdata
+!pkg/compiler/testdata
+!pkg/config/testdata
+!pkg/consensus/testdata
+!pkg/rpc/server/testdata
+!pkg/services/notary/testdata
+!pkg/services/oracle/testdata
+!pkg/smartcontract/testdata
+pkg/vm/testdata/fuzz
+!pkg/vm/testdata
+!pkg/wallet/testdata

pkg/vm/fuzz_test.go

@@ -0,0 +1,54 @@
+//go:build go1.18
+// +build go1.18
+
+package vm
+
+import (
+	"testing"
+
+	"github.com/nspcc-dev/neo-go/pkg/vm/opcode"
+	"github.com/stretchr/testify/require"
+)
+
+var fuzzSeedValidScripts = [][]byte{
+	makeProgram(opcode.PUSH1, opcode.PUSH10, opcode.ADD),
+	makeProgram(opcode.PUSH10, opcode.JMP, 3, opcode.ABORT, opcode.RET),
+	makeProgram(opcode.PUSHINT16, 1, 2, opcode.PUSHINT32, 3, 4, opcode.DROP),
+	makeProgram(opcode.PUSH2, opcode.NEWARRAY, opcode.DUP, opcode.PUSH0, opcode.PUSH1, opcode.SETITEM, opcode.VALUES),
+	append([]byte{byte(opcode.PUSHDATA1), 10}, randomBytes(10)...),
+	append([]byte{byte(opcode.PUSHDATA1), 100}, randomBytes(100)...),
+}
+
+func FuzzIsScriptCorrect(f *testing.F) {
+	for _, s := range fuzzSeedValidScripts {
+		f.Add(s)
+	}
+	f.Fuzz(func(t *testing.T, script []byte) {
+		require.NotPanics(t, func() {
+			_ = IsScriptCorrect(script, nil)
+		})
+	})
+}
+
+func FuzzVMDontPanic(f *testing.F) {
+	for _, s := range fuzzSeedValidScripts {
+		f.Add(s)
+	}
+	f.Fuzz(func(t *testing.T, script []byte) {
+		if IsScriptCorrect(script, nil) != nil {
+			return
+		}
+
+		v := load(script)
+
+		// Prevent infinite loops from being reported as fail.
+		v.GasLimit = 1000
+		v.getPrice = func(opcode.Opcode, []byte) int64 {
+			return 1
+		}
+
+		require.NotPanics(t, func() {
+			_ = v.Run()
+		})
+	})
+}