[gthumb/gthumb-3-4] SEGFAULT when a svg image could not be loaded

[Paolo Bacchilega <paobac src gnome org>]

commit f961196d1bbe01c706368eef581f01eeae273ed7
Author: Paolo Bacchilega <paobac src gnome org>
Date:   Fri Jul 14 08:47:13 2017 +0200

    SEGFAULT when a svg image could not be loaded
    
    [bug 784886]

 extensions/cairo_io/cairo-image-surface-svg.c |   18 +++++++++++++-----
 gthumb/gth-image-viewer.c                     |    5 ++++-
 2 files changed, 17 insertions(+), 6 deletions(-)
---
diff --git a/extensions/cairo_io/cairo-image-surface-svg.c b/extensions/cairo_io/cairo-image-surface-svg.c
index ee07770..75e6f48 100644
--- a/extensions/cairo_io/cairo-image-surface-svg.c
+++ b/extensions/cairo_io/cairo-image-surface-svg.c
@@ -140,22 +140,26 @@ gth_image_svg_new (void)
 }
 
 
-static void
+static gboolean
 gth_image_svg_set_handle (GthImageSvg *self,
                          RsvgHandle  *rsvg)
 {
        RsvgDimensionData dimension_data;
 
        if (self->rsvg == rsvg)
-               return;
+               return TRUE;
 
-       self->rsvg = g_object_ref (rsvg);
+       rsvg_handle_get_dimensions (rsvg, &dimension_data);
+       if ((dimension_data.width == 0) || (dimension_data.height == 0))
+               return FALSE;
 
-       rsvg_handle_get_dimensions (self->rsvg, &dimension_data);
+       self->rsvg = g_object_ref (rsvg);
        self->original_width = dimension_data.width;
        self->original_height = dimension_data.height;
 
        gth_image_svg_set_zoom (GTH_IMAGE (self), 1.0, NULL, NULL);
+
+       return TRUE;
 }
 
 
@@ -183,7 +187,11 @@ _cairo_image_surface_create_from_svg (GInputStream  *istream,
                                                 cancellable,
                                                 error);
        if (rsvg != NULL) {
-               gth_image_svg_set_handle (GTH_IMAGE_SVG (image), rsvg);
+               if (! gth_image_svg_set_handle (GTH_IMAGE_SVG (image), rsvg)) {
+                       g_set_error (error, G_IO_ERROR, G_IO_ERROR_INVALID_DATA, "Error");
+                       g_object_unref (image);
+                       image = NULL;
+               }
                g_object_unref (rsvg);
        }
 
diff --git a/gthumb/gth-image-viewer.c b/gthumb/gth-image-viewer.c
index 587c5f3..0bc45ad 100644
--- a/gthumb/gth-image-viewer.c
+++ b/gthumb/gth-image-viewer.c
@@ -815,7 +815,10 @@ image_has_alpha (GthImageViewer *viewer)
        if (image == NULL)
                return FALSE;
 
-       first_pixel = cairo_image_surface_get_data (image);
+       first_pixel = _cairo_image_surface_flush_and_get_data (image);
+       if (first_pixel == NULL)
+               return FALSE;
+
        return first_pixel[CAIRO_ALPHA] < 255;
 }