gif_deanimate(): Tolerate multiple image extensions in a row

[privoxy.git] / deanimate.c

diff --git a/deanimate.c b/deanimate.c
index bba74d4..7975122 100644 (file)
--- a/deanimate.c
+++ b/deanimate.c
@@ -10,7 +10,7 @@
  *                Privoxy team. https://www.privoxy.org/
  *
  *                Based on the GIF file format specification (see
- *                http://tronche.com/computer-graphics/gif/gif89a.html)
+ *                https://tronche.com/computer-graphics/gif/gif89a.html)
  *                and ideas from the Image::DeAnim Perl module by
  *                Ken MacFarlane, <ksm+cpan@universal.dca.net>
  *
@@ -131,6 +131,14 @@ static int buf_extend(struct binbuffer *buf, size_t length)
  *********************************************************************/
 static int buf_copy(struct binbuffer *src, struct binbuffer *dst, size_t length)
 {
+   /*
+    * Sanity check: Make sure the source buffer contains
+    * data and there's work to be done.
+    */
+   if (src->buffer == NULL || src->size == 0 || length == 0)
+   {
+      return 1;
+   }
 
    /*
     * Sanity check: Can't copy more data than we have
@@ -320,11 +328,16 @@ int gif_deanimate(struct binbuffer *src, struct binbuffer *dst, int get_first_im
 {
    unsigned char c;
    struct binbuffer *image;
+   int image_buffered = 0;
 
    if (NULL == src || NULL == dst)
    {
       return 1;
    }
+   if (src->size <= 10)
+   {
+      return 1;
+   }
 
    c = buf_getbyte(src, 10);
 
@@ -375,17 +388,25 @@ int gif_deanimate(struct binbuffer *src, struct binbuffer *dst, int get_first_im
       switch(buf_getbyte(src, 0))
       {
          /*
-          *  End-of-GIF Marker: Append current image and return
+          * End-of-GIF Marker: Append current image if we got
+          * one and return.
           */
       case 0x3b:
+         if (image->size == 0) goto failed;
          goto write;
 
          /*
           * Image block: Extract to current image buffer.
           */
       case 0x2c:
-         image->offset = 0;
+         if (image_buffered == 1)
+         {
+            /* Discard previous image. */
+            image->offset = 0;
+            image_buffered = 0;
+         }
          if (gif_extract_image(src, image)) goto failed;
+         image_buffered = 1;
          if (get_first_image) goto write;
          continue;
 
@@ -396,14 +417,16 @@ int gif_deanimate(struct binbuffer *src, struct binbuffer *dst, int get_first_im
          switch (buf_getbyte(src, 1))
          {
             /*
-             * Image extension: Copy extension  header and image
-             *                  to the current image buffer
+             * Image extension: Copy extension header
+             * and continue looking for new blocks.
              */
          case 0xf9:
-            image->offset = 0;
-            if (buf_copy(src, image, 8) || buf_getbyte(src, 0) != 0x2c) goto failed;
-            if (gif_extract_image(src, image)) goto failed;
-            if (get_first_image) goto write;
+            if (image_buffered == 1)
+            {
+               image->offset = 0;
+               image_buffered = 0;
+            }
+            if (buf_copy(src, image, 8)) goto failed;
             continue;
 
             /*