interop/contract: fix state rollbacks for nested contexts

Our wrapping optimization relied on the caller context having a TRY block,
but each context (including internal calls!) has an exception handling stack
of its own, which means that for an invocation stack of

    entry
    A.someMethodFromEntry()   # this one has a TRY
    A.internalMethodViaCALL() # this one doesn't
    B.someMethod()

we get `HasTryBlock() == false` for `A.internalMethodViaCALL()` context, which
leads to missing wrapper and missing rollbacks if B is to THROW. What this
patch does instead is it checks for any context within contract boundaries.

Fixes #3045.

Signed-off-by: Roman Khimov <roman@nspcc.ru>

pkg/core/interop/contract/call.go

@@ -117,7 +117,7 @@ func callExFromNative(ic *interop.Context, caller util.Uint160, cs *state.Contra
 	ic.Invocations[cs.Hash]++
 	f = ic.VM.Context().GetCallFlags() & f
 
-	wrapped := ic.VM.Context().HasTryBlock() && // If the method is not wrapped into try-catch block, then changes should be discarded anyway if exception occurs.
+	wrapped := ic.VM.ContractHasTryBlock() && // If the method is not wrapped into try-catch block, then changes should be discarded anyway if exception occurs.
 		f&(callflag.All^callflag.ReadOnly) != 0 // If the method is safe, then it's read-only and doesn't perform storage changes or emit notifications.
 	baseNtfCount := len(ic.Notifications)
 	baseDAO := ic.DAO

pkg/core/interop/contract/call_test.go

@@ -304,6 +304,9 @@ func TestSnapshotIsolation_Exceptions(t *testing.T) {
 			for i := 0; i < nNtfB1; i++ {
 				runtime.Notify("NotificationFromB before panic", i)
 			}
+			internalCaller(keyA, valueA, nNtfA)
+		}
+		func internalCaller(keyA, valueA []byte, nNtfA int) {
 			contract.Call(interop.Hash160{` + hashAStr + `}, "doAndPanic", contract.All, keyA, valueA, nNtfA)
 		}
 		func CheckStorageChanges() bool {

pkg/vm/context.go

@@ -315,16 +315,6 @@ func (v *VM) PushContextScriptHash(n int) error {
 	return nil
 }
 
-func (c *Context) HasTryBlock() bool {
-	for i := 0; i < c.tryStack.Len(); i++ {
-		eCtx := c.tryStack.Peek(i).Value().(*exceptionHandlingContext)
-		if eCtx.State == eTry {
-			return true
-		}
-	}
-	return false
-}
-
 // MarshalJSON implements the JSON marshalling interface.
 func (c *Context) MarshalJSON() ([]byte, error) {
 	var aux = contextAux{

pkg/vm/vm.go

@@ -1804,6 +1804,28 @@ func throwUnhandledException(item stackitem.Item) {
 	panic(msg)
 }
 
+// ContractHasTryBlock checks if the currently executing contract has a TRY
+// block in one of its contexts.
+func (v *VM) ContractHasTryBlock() bool {
+	var topctx *Context // Currently executing context.
+	for i := 0; i < len(v.istack); i++ {
+		ictx := v.istack[len(v.istack)-1-i] // It's a stack, going backwards like handleException().
+		if topctx == nil {
+			topctx = ictx
+		}
+		if ictx.sc != topctx.sc {
+			return false // Different contract -> no one cares.
+		}
+		for j := 0; j < ictx.tryStack.Len(); j++ {
+			eCtx := ictx.tryStack.Peek(j).Value().(*exceptionHandlingContext)
+			if eCtx.State == eTry {
+				return true
+			}
+		}
+	}
+	return false
+}
+
 // CheckMultisigPar checks if the sigs contains sufficient valid signatures.
 func CheckMultisigPar(v *VM, curve elliptic.Curve, h []byte, pkeys [][]byte, sigs [][]byte) bool {
 	if len(sigs) == 1 {