eth/tracers: pad memory slice on OOB case (#25213)

* eth/tracers: pad memory slice on oob case

* eth/tracers/js: fix testfailure due to err msg capitalization
Co-authored-by: Martin Holst Swende <martin@swende.se>

eth/tracers/js/goja.go

@@ -33,6 +33,10 @@ import (
 	jsassets "github.com/ethereum/go-ethereum/eth/tracers/js/internal/tracers"
 )
 
+const (
+	memoryPadLimit = 1024 * 1024
+)
+
 var assetTracers = make(map[string]string)
 
 // init retrieves the JavaScript transaction tracers included in go-ethereum.
@@ -562,10 +566,15 @@ func (mo *memoryObj) slice(begin, end int64) ([]byte, error) {
 	if end < begin || begin < 0 {
 		return nil, fmt.Errorf("tracer accessed out of bound memory: offset %d, end %d", begin, end)
 	}
-	if mo.memory.Len() < int(end) {
-		return nil, fmt.Errorf("tracer accessed out of bound memory: available %d, offset %d, size %d", mo.memory.Len(), begin, end-begin)
+	mlen := mo.memory.Len()
+	if end-int64(mlen) > memoryPadLimit {
+		return nil, fmt.Errorf("tracer reached limit for padding memory slice: end %d, memorySize %d", end, mlen)
 	}
-	return mo.memory.GetCopy(begin, end-begin), nil
+	slice := make([]byte, end-begin)
+	end = min(end, int64(mo.memory.Len()))
+	ptr := mo.memory.GetPtr(begin, end-begin)
+	copy(slice[:], ptr[:])
+	return slice, nil
 }
 
 func (mo *memoryObj) GetUint(addr int64) goja.Value {
@@ -945,3 +954,10 @@ func (l *steplog) setupObject() *goja.Object {
 	o.Set("contract", l.contract.setupObject())
 	return o
 }
+
+func min(a, b int64) int64 {
+	if a < b {
+		return a
+	}
+	return b
+}

eth/tracers/js/tracer_test.go

@@ -60,7 +60,7 @@ func testCtx() *vmContext {
 	return &vmContext{blockCtx: vm.BlockContext{BlockNumber: big.NewInt(1)}, txCtx: vm.TxContext{GasPrice: big.NewInt(100000)}}
 }
 
-func runTrace(tracer tracers.Tracer, vmctx *vmContext, chaincfg *params.ChainConfig) (json.RawMessage, error) {
+func runTrace(tracer tracers.Tracer, vmctx *vmContext, chaincfg *params.ChainConfig, contractCode []byte) (json.RawMessage, error) {
 	var (
 		env             = vm.NewEVM(vmctx.blockCtx, vmctx.txCtx, &dummyStatedb{}, chaincfg, vm.Config{Debug: true, Tracer: tracer})
 		gasLimit uint64 = 31000
@@ -69,6 +69,9 @@ func runTrace(tracer tracers.Tracer, vmctx *vmContext, chaincfg *params.ChainCon
 		contract        = vm.NewContract(account{}, account{}, value, startGas)
 	)
 	contract.Code = []byte{byte(vm.PUSH1), 0x1, byte(vm.PUSH1), 0x1, 0x0}
+	if contractCode != nil {
+		contract.Code = contractCode
+	}
 
 	tracer.CaptureTxStart(gasLimit)
 	tracer.CaptureStart(env, contract.Caller(), contract.Address(), false, []byte{}, startGas, value)
@@ -83,22 +86,23 @@ func runTrace(tracer tracers.Tracer, vmctx *vmContext, chaincfg *params.ChainCon
 }
 
 func TestTracer(t *testing.T) {
-	execTracer := func(code string) ([]byte, string) {
+	execTracer := func(code string, contract []byte) ([]byte, string) {
 		t.Helper()
 		tracer, err := newJsTracer(code, nil, nil)
 		if err != nil {
 			t.Fatal(err)
 		}
-		ret, err := runTrace(tracer, testCtx(), params.TestChainConfig)
+		ret, err := runTrace(tracer, testCtx(), params.TestChainConfig, contract)
 		if err != nil {
 			return nil, err.Error() // Stringify to allow comparison without nil checks
 		}
 		return ret, ""
 	}
 	for i, tt := range []struct {
-		code string
-		want string
-		fail string
+		code     string
+		want     string
+		fail     string
+		contract []byte
 	}{
 		{ // tests that we don't panic on bad arguments to memory access
 			code: "{depths: [], step: function(log) { this.depths.push(log.memory.slice(-1,-2)); }, fault: function() {}, result: function() { return this.depths; }}",
@@ -139,9 +143,18 @@ func TestTracer(t *testing.T) {
 		}, {
 			code: "{res: null, step: function(log) { var address = Array.prototype.slice.call(log.contract.getAddress()); this.res = toAddress(address); }, fault: function() {}, result: function() { return this.res }}",
 			want: `{"0":0,"1":0,"2":0,"3":0,"4":0,"5":0,"6":0,"7":0,"8":0,"9":0,"10":0,"11":0,"12":0,"13":0,"14":0,"15":0,"16":0,"17":0,"18":0,"19":0}`,
+		}, {
+			code:     "{res: [], step: function(log) { var op = log.op.toString(); if (op === 'MSTORE8' || op === 'STOP') { this.res.push(log.memory.slice(0, 2)) } }, fault: function() {}, result: function() { return this.res }}",
+			want:     `[{"0":0,"1":0},{"0":255,"1":0}]`,
+			contract: []byte{byte(vm.PUSH1), byte(0xff), byte(vm.PUSH1), byte(0x00), byte(vm.MSTORE8), byte(vm.STOP)},
+		}, {
+			code:     "{res: [], step: function(log) { if (log.op.toString() === 'STOP') { this.res.push(log.memory.slice(5, 1025 * 1024)) } }, fault: function() {}, result: function() { return this.res }}",
+			want:     "",
+			fail:     "tracer reached limit for padding memory slice: end 1049600, memorySize 32 at step (<eval>:1:83(23))    in server-side tracer function 'step'",
+			contract: []byte{byte(vm.PUSH1), byte(0xff), byte(vm.PUSH1), byte(0x00), byte(vm.MSTORE8), byte(vm.STOP)},
 		},
 	} {
-		if have, err := execTracer(tt.code); tt.want != string(have) || tt.fail != err {
+		if have, err := execTracer(tt.code, tt.contract); tt.want != string(have) || tt.fail != err {
 			t.Errorf("testcase %d: expected return value to be '%s' got '%s', error to be '%s' got '%s'\n\tcode: %v", i, tt.want, string(have), tt.fail, err, tt.code)
 		}
 	}
@@ -157,7 +170,7 @@ func TestHalt(t *testing.T) {
 		time.Sleep(1 * time.Second)
 		tracer.Stop(timeout)
 	}()
-	if _, err = runTrace(tracer, testCtx(), params.TestChainConfig); !strings.Contains(err.Error(), "stahp") {
+	if _, err = runTrace(tracer, testCtx(), params.TestChainConfig, nil); !strings.Contains(err.Error(), "stahp") {
 		t.Errorf("Expected timeout error, got %v", err)
 	}
 }
@@ -227,7 +240,7 @@ func TestIsPrecompile(t *testing.T) {
 	}
 
 	blockCtx := vm.BlockContext{BlockNumber: big.NewInt(150)}
-	res, err := runTrace(tracer, &vmContext{blockCtx, txCtx}, chaincfg)
+	res, err := runTrace(tracer, &vmContext{blockCtx, txCtx}, chaincfg, nil)
 	if err != nil {
 		t.Error(err)
 	}
@@ -237,7 +250,7 @@ func TestIsPrecompile(t *testing.T) {
 
 	tracer, _ = newJsTracer("{addr: toAddress('0000000000000000000000000000000000000009'), res: null, step: function() { this.res = isPrecompiled(this.addr); }, fault: function() {}, result: function() { return this.res; }}", nil, nil)
 	blockCtx = vm.BlockContext{BlockNumber: big.NewInt(250)}
-	res, err = runTrace(tracer, &vmContext{blockCtx, txCtx}, chaincfg)
+	res, err = runTrace(tracer, &vmContext{blockCtx, txCtx}, chaincfg, nil)
 	if err != nil {
 		t.Error(err)
 	}