Fix a potential stack overflow bug with GIF images (Issue #470)

Author: michaelrsweet

CHANGES.md

@@ -7,6 +7,7 @@
 - Fixed a potential stack overflow bug with BMP images (Issue #466)
 - Fixed a potential heap overflow bug with the table-of-contents (Issue #467)
 - Fixed a potential heap overflow bug with headings (Issue #468)
+- Fixed a potential stack overflow bug with GIF images (Issue #470)
 
 
 # Changes in HTMLDOC v1.9.14

htmldoc/image.cxx

@@ -465,7 +465,6 @@ gif_read_lzw(FILE *fp,			/* I - File to read from */
     {
       uchar	buf[260];
 
-
       if (!gif_eof)
         while (gif_get_block(fp, buf) > 0);
 
@@ -482,17 +481,23 @@ gif_read_lzw(FILE *fp,			/* I - File to read from */
 
     while (code >= clear_code)
     {
+      if (sp >= (stack + sizeof(stack)))
+        return (255);
+
       *sp++ = table[1][code];
+
       if (code == table[0][code])
 	return (255);
 
       code = table[0][code];
     }
 
+    if (sp >= (stack + sizeof(stack)))
+      return (255);
+
     *sp++ = firstcode = table[1][code];
-    code  = max_code;
 
-    if (code < 4096)
+    if ((code = max_code) < 4096)
     {
       table[0][code] = oldcode;
       table[1][code] = firstcode;