Commit message: Bug 790849 - (CVE-2017-17789) CVE-2017-17789 Heap buffer overflow...

... in PSP importer.
Check if declared block length is valid (i.e. within the actual file)
before going further.
Consider the file as broken otherwise and fail loading it.
CVE: CVE-2017-17789
CWE: CWE-787
Vulnerability description: In GIMP 2.8.22, there is a heap-based buffer overflow in read_channel_data in plug-ins/common/file-psp.c.

Project: GIMP

load_image (const gchar  *filename,
            GError      **error)
{
  FILE *f;
  struct stat st;
  char buf[32];
  PSPimage ia;
  guint32 block_init_len, block_total_len;
  long block_start;
  PSPBlockID id = -1;
  gint block_number;

  gint32 image_ID = -1;

  if (g_stat (filename, &st) == -1)
    return -1;

  f = g_fopen (filename, "rb");
  if (f == NULL)
    {
      g_set_error (error, G_FILE_ERROR, g_file_error_from_errno (errno),
                   _("Could not open '%s' for reading: %s"),
                   gimp_filename_to_utf8 (filename), g_strerror (errno));
      return -1;
    }

  /* Read the PSP File Header and determine file version */
  if (fread (buf, 32, 1, f) < 1
      || fread (&psp_ver_major, 2, 1, f) < 1
      || fread (&psp_ver_minor, 2, 1, f) < 1)
    {
      g_message ("Error reading file header");
      goto error;
    }

  if (memcmp (buf, "Paint Shop Pro Image File\n\032\0\0\0\0\0", 32) != 0)
    {
      g_message ("Incorrect file signature");
      goto error;
    }

  psp_ver_major = GUINT16_FROM_LE (psp_ver_major);
  psp_ver_minor = GUINT16_FROM_LE (psp_ver_minor);

  /* I only have the documentation for file format version 3.0,
   * but PSP 6 writes version 4.0. Let's hope it's backwards compatible.
   * Earlier versions probably don't have all the fields I expect
   * so don't accept those.
   */
  if (psp_ver_major < 3)
    {
      g_message ("Unsupported PSP file format version "
                 "%d.%d, only knows 3.0 (and later?)",
                 psp_ver_major, psp_ver_minor);
      goto error;
    }
  else if ((psp_ver_major == 3)
        || (psp_ver_major == 4)
        || (psp_ver_major == 5)
        || (psp_ver_major == 6))
    ; /* OK */
  else
    {
      g_message ("Unsupported PSP file format version %d.%d",
                 psp_ver_major, psp_ver_minor);
      goto error;
    }

  /* Read all the blocks */
  block_number = 0;

  IFDBG(3) g_message ("size = %d", (int)st.st_size);
  while (ftell (f) != st.st_size
         && (id = read_block_header (f, &block_init_len,
                                     &block_total_len)) != -1)
    {
      block_start = ftell (f);

      if (id == PSP_IMAGE_BLOCK)
        {
          if (block_number != 0)
            {
              g_message ("Duplicate General Image Attributes block");
              goto error;
            }
          if (read_general_image_attribute_block (f, block_init_len,
                                                  block_total_len, &ia) == -1)
            {
              goto error;
            }

          IFDBG(2) g_message ("%d dpi %dx%d %s",
                              (int) ia.resolution,
                              ia.width, ia.height,
                              compression_name (ia.compression));

          image_ID = gimp_image_new (ia.width, ia.height,
                                     ia.grayscale ? GIMP_GRAY : GIMP_RGB);
          if (image_ID == -1)
            {
              goto error;
            }

          gimp_image_set_filename (image_ID, filename);

          gimp_image_set_resolution (image_ID, ia.resolution, ia.resolution);
        }
      else
        {
          if (block_number == 0)
            {
              g_message ("Missing General Image Attributes block");
              goto error;
            }

          switch (id)
            {
            case PSP_CREATOR_BLOCK:
              if (read_creator_block (f, image_ID, block_total_len, &ia) == -1)
                goto error;
              break;

            case PSP_COLOR_BLOCK:
              break;            /* Not yet implemented */

            case PSP_LAYER_START_BLOCK:
              if (read_layer_block (f, image_ID, block_total_len, &ia) == -1)
                goto error;
              break;

            case PSP_SELECTION_BLOCK:
              break;            /* Not yet implemented */

            case PSP_ALPHA_BANK_BLOCK:
              break;            /* Not yet implemented */

            case PSP_THUMBNAIL_BLOCK:
              break;            /* No use for it */

            case PSP_EXTENDED_DATA_BLOCK:
              break;            /* Not yet implemented */

            case PSP_TUBE_BLOCK:
              if (read_tube_block (f, image_ID, block_total_len, &ia) == -1)
                goto error;
              break;

            case PSP_COMPOSITE_IMAGE_BANK_BLOCK:
              break;            /* Not yet implemented */

            case PSP_LAYER_BLOCK:
            case PSP_CHANNEL_BLOCK:
            case PSP_ALPHA_CHANNEL_BLOCK:
            case PSP_ADJUSTMENT_EXTENSION_BLOCK:
            case PSP_VECTOR_EXTENSION_BLOCK:
            case PSP_SHAPE_BLOCK:
            case PSP_PAINTSTYLE_BLOCK:
            case PSP_COMPOSITE_ATTRIBUTES_BLOCK:
            case PSP_JPEG_BLOCK:
              g_message ("Sub-block %s should not occur "
                         "at main level of file",
                         block_name (id));
              break;

            default:
              g_message ("Unrecognized block id %d", id);
              break;
            }
        }

      if (block_start + block_total_len >= st.st_size)
        break;

      if (try_fseek (f, block_start + block_total_len, SEEK_SET) < 0)
        goto error;

      block_number++;
    }

  if (id == -1)
    {
    error:
      fclose (f);
      if (image_ID != -1)
        gimp_image_delete (image_ID);
      return -1;
    }

  fclose (f);

  return image_ID;
}