Fix heap buffer overflow in Cycles IES parser

The IES parser in Cycles would lead to heap buffer overflow error
when non-supported or invalid data is provided to it.

The error was caused by the way how stirng is copied to vector
skipping the last null-terminator. Later C-style string utilities
are used for parsing, and they expect the data to be null-terminated.

It is unclear why data needs to be stored as vector: storing it as
string simplifies initialization.

Easiest to reproduce the issue is to use Blender build with address
sanitizer enabled.

Pull Request: https://projects.blender.org/blender/blender/pulls/116752

intern/cycles/test/CMakeLists.txt

@@ -32,6 +32,7 @@ set(SRC
   integrator_tile_test.cpp
   render_graph_finalize_test.cpp
   util_aligned_malloc_test.cpp
+  util_ies_test.cpp
   util_math_test.cpp
   util_md5_test.cpp
   util_path_test.cpp

intern/cycles/test/util_ies_test.cpp

@@ -0,0 +1,18 @@
+/* SPDX-FileCopyrightText: 2011-2024 Blender Foundation
+ *
+ * SPDX-License-Identifier: Apache-2.0 */
+
+#include "testing/testing.h"
+
+#include "util/ies.h"
+
+CCL_NAMESPACE_BEGIN
+
+TEST(util_ies, invalid)
+{
+  IESFile ies_file;
+
+  EXPECT_FALSE(ies_file.load("Hello, World!"));
+}
+
+CCL_NAMESPACE_END

intern/cycles/util/ies.cpp

@@ -63,11 +63,11 @@ void IESFile::pack(float *data)
 
 class IESTextParser {
  public:
-  vector<char> text;
+  string text;
   char *data;
   bool error;
 
-  IESTextParser(const string &str) : text(str.begin(), str.end()), error(false)
+  IESTextParser(const string &str) : text(str), error(false)
   {
     std::replace(text.begin(), text.end(), ',', ' ');
     data = strstr(&text[0], "\nTILT=");