gif_fix_image_counter.patch

diff --git a/dgif_lib.c b/dgif_lib.c
index 82fc097..214a0e7 100644
--- a/dgif_lib.c
+++ b/dgif_lib.c
@@ -810,7 +810,8 @@ DGifSetupDecompress(GifFileType *GifFile)
 
     /* coverity[check_return] */
     if (InternalRead(GifFile, &CodeSize, 1) < 1) {    /* Read Code size from file. */
-	return GIF_ERROR;    /* Failed to read Code size. */
+        GifFile->Error = D_GIF_ERR_READ_FAILED;
+        return GIF_ERROR;    /* Failed to read Code size. */
     }
     BitsPerPixel = CodeSize;
 
@@ -1118,6 +1119,31 @@ DGifBufferedInput(GifFileType *GifFile, GifByteType *Buf, GifByteType *NextByte)
     return GIF_OK;
 }
 
+/******************************************************************************
+ This routine is called in case of error during parsing image. We need to
+ decrease image counter and reallocate memory for saved images. Not decreasing
+ ImageCount may lead to null pointer dereference, because the last element in
+ SavedImages may point to the spoilt image and null pointer buffers. 
+*******************************************************************************/
+void
+DGifDecreaseImageCounter(GifFileType *GifFile)
+{
+    GifFile->ImageCount--;
+    if (GifFile->SavedImages[GifFile->ImageCount].RasterBits != NULL) {
+        free(GifFile->SavedImages[GifFile->ImageCount].RasterBits);
+    }
+    if (GifFile->SavedImages[GifFile->ImageCount].ImageDesc.ColorMap != NULL) {
+        GifFreeMapObject(GifFile->SavedImages[GifFile->ImageCount].ImageDesc.ColorMap);
+    }
+    
+    // Realloc array according to the new image counter.
+    SavedImage *correct_saved_images = (SavedImage *)reallocarray(
+        GifFile->SavedImages, GifFile->ImageCount, sizeof(SavedImage));
+    if (correct_saved_images != NULL) {
+        GifFile->SavedImages = correct_saved_images;
+    }
+}
+
 /******************************************************************************
  This routine reads an entire GIF into core, hanging all its state info off
  the GifFileType pointer.  Call DGifOpenFileName() or DGifOpenFileHandle()
@@ -1148,17 +1174,20 @@ DGifSlurp(GifFileType *GifFile)
               /* Allocate memory for the image */
               if (sp->ImageDesc.Width <= 0 || sp->ImageDesc.Height <= 0 ||
                       sp->ImageDesc.Width > (INT_MAX / sp->ImageDesc.Height)) {
+                  DGifDecreaseImageCounter(GifFile);
                   return GIF_ERROR;
               }
               ImageSize = sp->ImageDesc.Width * sp->ImageDesc.Height;
 
               if (ImageSize > (SIZE_MAX / sizeof(GifPixelType))) {
+                  DGifDecreaseImageCounter(GifFile);
                   return GIF_ERROR;
               }
               sp->RasterBits = (unsigned char *)reallocarray(NULL, ImageSize,
                       sizeof(GifPixelType));
 
               if (sp->RasterBits == NULL) {
+                  DGifDecreaseImageCounter(GifFile);
                   return GIF_ERROR;
               }
 
@@ -1177,13 +1206,17 @@ DGifSlurp(GifFileType *GifFile)
 			   j += InterlacedJumps[i]) {
 			  if (DGifGetLine(GifFile, 
 					  sp->RasterBits+j*sp->ImageDesc.Width, 
-					  sp->ImageDesc.Width) == GIF_ERROR)
-			      return GIF_ERROR;
+					  sp->ImageDesc.Width) == GIF_ERROR) {
+                              DGifDecreaseImageCounter(GifFile);
+                              return GIF_ERROR;
+                          }
 		      }
 	      }
 	      else {
-		  if (DGifGetLine(GifFile,sp->RasterBits,ImageSize)==GIF_ERROR)
-		      return (GIF_ERROR);
+                  if (DGifGetLine(GifFile,sp->RasterBits,ImageSize)==GIF_ERROR) {
+                      DGifDecreaseImageCounter(GifFile);
+                      return GIF_ERROR;
+                  }
 	      }
 
               if (GifFile->ExtensionBlocks) {