Avoid out-of-bounds access when checking file extensions.

Include the '.' in the file extension check.

PiperOrigin-RevId: 474866478
Change-Id: I809ae975e4c8b00f17278735975a7d07e0748643

src/user/user_mesh.cc

@@ -160,12 +160,12 @@ void mjCMesh::Compile(const mjVFS* vfs) {
     }
 
     // load STL, OBJ or MSH
-    string ext = file.substr(file.size()-3, 3);
-    if (!strcasecmp(ext.c_str(), "stl")) {
+    string ext = mjuu_getext(file);
+    if (!strcasecmp(ext.c_str(), ".stl")) {
       LoadSTL(vfs);
-    } else if (!strcasecmp(ext.c_str(), "obj")) {
+    } else if (!strcasecmp(ext.c_str(), ".obj")) {
       LoadOBJ(vfs);
-    } else if (!strcasecmp(ext.c_str(), "msh")) {
+    } else if (!strcasecmp(ext.c_str(), ".msh")) {
       LoadMSH(vfs);
     } else {
       throw mjCError(this, "Unknown mesh file type: %s", file.c_str());
@@ -1621,8 +1621,8 @@ void mjCSkin::Compile(const mjVFS* vfs) {
     }
 
     // load SKN
-    string ext = file.substr(file.size()-3, 3);
-    if (!strcasecmp(ext.c_str(), "skn")) {
+    string ext = mjuu_getext(file);
+    if (!strcasecmp(ext.c_str(), ".skn")) {
       LoadSKN(vfs);
     } else {
       throw mjCError(this, "Unknown skin file type: %s", file.c_str());

src/user/user_objects.cc

@@ -1879,7 +1879,8 @@ void mjCHField::Compile(const mjVFS* vfs) {
     string filename = mjuu_makefullname(model->modelfiledir, model->meshdir, file);
 
     // load depending on format
-    if (!strcasecmp(filename.substr(filename.length()-4, 5).c_str(), ".png")) {
+    string ext = mjuu_getext(filename);
+    if (!strcasecmp(ext.c_str(), ".png")) {
       LoadPNG(filename, vfs);
     } else {
       LoadCustom(filename, vfs);
@@ -2301,7 +2302,8 @@ void mjCTexture::LoadFlip(string filename, const mjVFS* vfs,
                           std::vector<unsigned char>& image,
                           unsigned int& w, unsigned int& h) {
   // dispatch to PNG or Custom loaded
-  if (!strcasecmp(filename.substr(filename.length()-4, 5).c_str(), ".png")) {
+  string ext = mjuu_getext(filename);
+  if (!strcasecmp(ext.c_str(), ".png")) {
     LoadPNG(filename, vfs, image, w, h);
   } else {
     LoadCustom(filename, vfs, image, w, h);

src/user/user_util.cc

@@ -19,6 +19,7 @@
 #include <cstdio>
 #include <limits>
 #include <string>
+#include <string_view>
 
 #include <mujoco/mjtnum.h>
 #include "engine/engine_macro.h"
@@ -488,9 +489,16 @@ string mjuu_stripext(string filename) {
   }
 
   // return name without extension
-  else {
-    return filename.substr(0, end);
+  return filename.substr(0, end);
+}
+
+string mjuu_getext(std::string_view filename) {
+  size_t dot = filename.find_last_of('.');
+
+  if (dot==string::npos) {
+    return "";
   }
+  return string(filename.substr(dot, filename.size() - dot));
 }
 
 

src/user/user_util.h

@@ -16,6 +16,7 @@
 #define MUJOCO_SRC_USER_USER_UTIL_H_
 
 #include <string>
+#include <string_view>
 
 
 extern const double mjNAN;                      // used to mark undefined fields
@@ -129,6 +130,9 @@ std::string mjuu_strippath(std::string filename);
 // strip extension from filename
 std::string mjuu_stripext(std::string filename);
 
+// get the extension of a filename
+std::string mjuu_getext(std::string_view filename);
+
 // check if path is absolute
 bool mjuu_isabspath(std::string path);