From e7dd180447288c27ef087d36b3f56d1b3e9ca58f Mon Sep 17 00:00:00 2001
From: Egon Elbre <egonelbre@gmail.com>
Date: Sat, 2 Jul 2022 15:37:09 +0300
Subject: [PATCH] internal/ops: avoid some bounds checks in decode

Signed-off-by: Egon Elbre <egonelbre@gmail.com>
---
 internal/ops/ops.go    | 3 ++-
 internal/ops/reader.go | 6 +++---
 2 files changed, 5 insertions(+), 4 deletions(-)

diff --git a/internal/ops/ops.go b/internal/ops/ops.go
index 3691c272..c68a51ee 100644
--- a/internal/ops/ops.go
+++ b/internal/ops/ops.go
@@ -163,9 +163,10 @@ const (
 )
 
 func (op *ClipOp) Decode(data []byte) {
-	if OpType(data[0]) != TypeClip {
+	if len(data) < TypeClipLen || OpType(data[0]) != TypeClip {
 		panic("invalid op")
 	}
+	data = data[:TypeClipLen]
 	bo := binary.LittleEndian
 	r := image.Rectangle{
 		Min: image.Point{
diff --git a/internal/ops/reader.go b/internal/ops/reader.go
index 63ec9cc3..b7f0f006 100644
--- a/internal/ops/reader.go
+++ b/internal/ops/reader.go
@@ -160,7 +160,7 @@ func (r *Reader) Decode() (EncodedOp, bool) {
 }
 
 func (op *opMacroDef) decode(data []byte) {
-	if OpType(data[0]) != TypeMacro {
+	if len(data) < TypeMacroLen || OpType(data[0]) != TypeMacro {
 		panic("invalid op")
 	}
 	bo := binary.LittleEndian
@@ -176,11 +176,11 @@ func (op *opMacroDef) decode(data []byte) {
 }
 
 func (m *macroOp) decode(data []byte, refs []interface{}) {
-	if OpType(data[0]) != TypeCall {
+	if len(data) < TypeCallLen || len(refs) < 1 || OpType(data[0]) != TypeCall {
 		panic("invalid op")
 	}
-	data = data[:TypeCallLen]
 	bo := binary.LittleEndian
+	data = data[:TypeCallLen]
 	*m = macroOp{
 		ops: refs[0].(*Ops),
 		start: PC{