[libpng14] Prevent writing over-length PLTE chunk (Cosmin Truta) and

silently truncate over-length PLTE chunk while reading.

libpng.3

@@ -3586,6 +3586,11 @@ PNG_QUANTIZE_[RED,GREEN,BLUE]_BITS.
 
 We removed the trailing '.' from the warning and error messages.
 
+Starting with libpng-1.4.17, attempting to set an over-length PLTE chunk
+is an error. Previously this requirement of the PNG specification was not
+enforced, and the palette was always limited to 256 entries. An over-length
+PLTE chunk found in an input PNG is silently truncated.
+
 .SH X. Detecting libpng
 
 The png_get_io_ptr() function has been present since libpng-0.88, has never

pngrutil.c

@@ -551,7 +551,7 @@ void /* PRIVATE */
 png_handle_PLTE(png_structp png_ptr, png_infop info_ptr, png_uint_32 length)
 {
    png_color palette[PNG_MAX_PALETTE_LENGTH];
-   int num, i;
+   int max_palette_length, num, i;
 #ifdef PNG_POINTER_INDEXING_SUPPORTED
    png_colorp pal_ptr;
 #endif
@@ -603,8 +603,19 @@ png_handle_PLTE(png_structp png_ptr, png_infop info_ptr, png_uint_32 length)
       }
    }
 
+   max_palette_length = (png_ptr->color_type == PNG_COLOR_TYPE_PALETTE) ?
+      (1 << png_ptr->bit_depth) : PNG_MAX_PALETTE_LENGTH;
+
+   /* The cast is safe because 'length' is less than 3*PNG_MAX_PALETTE_LENGTH */
    num = (int)length / 3;
 
+   /* If the palette has 256 or fewer entries but is too large for the bit depth,
+    * we don't issue an error, to preserve the behavior of previous libpng versions.
+    * We silently truncate the unused extra palette entries here.
+    */
+   if (num > max_palette_length)
+     num = max_palette_length;
+
 #ifdef PNG_POINTER_INDEXING_SUPPORTED
    for (i = 0, pal_ptr = palette; i < num; i++, pal_ptr++)
    {

pngset.c

@@ -1,7 +1,7 @@
 
 /* pngset.c - storage of image information into info struct
  *
- * Last changed in libpng 1.4.17 [October 28, 2015]
+ * Last changed in libpng 1.4.17 [October 31, 2015]
  * Copyright (c) 1998-2015 Glenn Randers-Pehrson
  * (Version 0.96 Copyright (c) 1996, 1997 Andreas Dilger)
  * (Version 0.88 Copyright (c) 1995, 1996 Guy Eric Schalnat, Group 42, Inc.)
@@ -427,12 +427,17 @@ png_set_PLTE(png_structp png_ptr, png_infop info_ptr,
    png_colorp palette, int num_palette)
 {
 
+   png_uint_32 max_palette_length;
+
    png_debug1(1, "in %s storage function", "PLTE");
 
    if (png_ptr == NULL || info_ptr == NULL)
       return;
 
-   if (num_palette < 0 || num_palette > PNG_MAX_PALETTE_LENGTH)
+   max_palette_length = (png_ptr->color_type == PNG_COLOR_TYPE_PALETTE) ?
+      (1 << png_ptr->bit_depth) : PNG_MAX_PALETTE_LENGTH;
+
+   if (num_palette < 0 || num_palette > (int) max_palette_length)
    {
       if (info_ptr->color_type == PNG_COLOR_TYPE_PALETTE)
          png_error(png_ptr, "Invalid palette length");
@@ -450,8 +455,8 @@ png_set_PLTE(png_structp png_ptr, png_infop info_ptr,
    png_free_data(png_ptr, info_ptr, PNG_FREE_PLTE, 0);
 
    /* Changed in libpng-1.2.1 to allocate PNG_MAX_PALETTE_LENGTH instead
-    * of num_palette entries, in case of an invalid PNG file that has
+    * of num_palette entries, in case of an invalid PNG file or incorrect
-    * too-large sample values.
+    * call to png_set_PLTE() with too-large sample values.
     */
    png_ptr->palette = (png_colorp)png_calloc(png_ptr,
       PNG_MAX_PALETTE_LENGTH * png_sizeof(png_color));

pngwutil.c

@@ -601,17 +601,20 @@ void /* PRIVATE */
 png_write_PLTE(png_structp png_ptr, png_colorp palette, png_uint_32 num_pal)
 {
    PNG_PLTE;
-   png_uint_32 i;
+   png_uint_32 max_palette_length, i;
    png_colorp pal_ptr;
    png_byte buf[3];
 
    png_debug(1, "in png_write_PLTE");
 
+   max_palette_length = (png_ptr->color_type == PNG_COLOR_TYPE_PALETTE) ?
+      (1 << png_ptr->bit_depth) : PNG_MAX_PALETTE_LENGTH;
+
    if ((
 #ifdef PNG_MNG_FEATURES_SUPPORTED
         !(png_ptr->mng_features_permitted & PNG_FLAG_MNG_EMPTY_PLTE) &&
 #endif
-        num_pal == 0) || num_pal > 256)
+        num_pal == 0) || num_pal > max_palette_length)
    {
      if (png_ptr->color_type == PNG_COLOR_TYPE_PALETTE)
      {