protect against invalid chunk lengths in some tools

4 files changed, 19 insertions, 3 deletions

diff --git a/example_png_info.cpp b/example_png_info.cpp
index 86f664a..e7f78a2 100644
--- a/example_png_info.cpp
+++ b/example_png_info.cpp
@@ -232,6 +232,10 @@ void displayFilterTypes(const std::vector<unsigned char>& buffer)
     {
       const unsigned char* cdata = lodepng_chunk_data_const(chunk);
       unsigned clength = lodepng_chunk_length(chunk);
+      if(chunk + clength >= end) {
+        std::cout << "invalid chunk length" << std::endl;
+        return;
+      }
 
       for(unsigned i = 0; i < clength; i++)
       {
diff --git a/lodepng.h b/lodepng.h
index ef2c820..8e2e038 100644
--- a/lodepng.h
+++ b/lodepng.h
@@ -677,7 +677,11 @@ Third byte: must be uppercase
 Fourth byte: uppercase = unsafe to copy, lowercase = safe to copy
 */
 
-/*get the length of the data of the chunk. Total chunk length has 12 bytes more.*/
+/*
+Gets the length of the data of the chunk. Total chunk length has 12 bytes more.
+There must be at least 4 bytes to read from. If the result value is too large,
+it may be corrupt data.
+*/
 unsigned lodepng_chunk_length(const unsigned char* chunk);
 
 /*puts the 4-byte type in null terminated string*/
diff --git a/lodepng_util.cpp b/lodepng_util.cpp
index 3784b6e..ed054f0 100644
--- a/lodepng_util.cpp
+++ b/lodepng_util.cpp
@@ -51,8 +51,10 @@ unsigned getChunkInfo(std::vector<std::string>& names, std::vector<size_t>& size
     lodepng_chunk_type(type, chunk);
     if(std::string(type).size() != 4) return 1;
 
+    unsigned length = lodepng_chunk_length(chunk);
+    if(chunk + length >= end) return 1;
     names.push_back(type);
-    sizes.push_back(lodepng_chunk_length(chunk));
+    sizes.push_back(length);
 
     chunk = lodepng_chunk_next_const(chunk);
   }
@@ -180,6 +182,7 @@ unsigned getFilterTypesInterlaced(std::vector<std::vector<unsigned char> >& filt
     {
       const unsigned char* cdata = lodepng_chunk_data_const(chunk);
       unsigned clength = lodepng_chunk_length(chunk);
+      if(chunk + clength >= end) return 1; // corrupt chunk length
 
       for(unsigned i = 0; i < clength; i++)
       {
diff --git a/pngdetail.cpp b/pngdetail.cpp
index b876f71..98f03d2 100644
--- a/pngdetail.cpp
+++ b/pngdetail.cpp
@@ -304,7 +304,12 @@ Show the filtertypes of each scanline in this PNG image.
 void displayFilterTypes(const std::vector<unsigned char>& buffer)
 {
   std::vector<std::vector<unsigned char> > types;
-  lodepng::getFilterTypesInterlaced(types, buffer);
+  unsigned error = lodepng::getFilterTypesInterlaced(types, buffer);
+  if(error)
+  {
+    std::cout << "Error getting filter types" << std::endl;
+    return;
+  }
 
   if(types.size() == 7)
   {