[surface] Protect against the user setting a fallback resolution of 0.

Bug 23067 -- using clear drawing operator crashes printing
http://bugs.freedesktop.org/show_bug.cgi?id=23067

Here we were hitting an assert within the paginated surface after creating
a zero sized fallback image, due to the paginated surface being created
with an x fallback resolution of 0 dpi (by
_gtk_printer_create_cairo_surface(), gtk/gtkprinter.c:924).

Avoid the bug by guarding against bad input to
cairo_surface_set_fallback_resolution() which also allows us to identity
the invalid caller.

1 files changed, 8 insertions, 0 deletions

diff --git a/src/cairo-surface.c b/src/cairo-surface.c
index f656ed5f..8c8b8677 100644
--- a/src/cairo-surface.c
+++ b/src/cairo-surface.c
@@ -1218,6 +1218,14 @@ cairo_surface_set_fallback_resolution (cairo_surface_t	*surface,
 	return;
     }
 
+    if (x_pixels_per_inch <= 0 || y_pixels_per_inch <= 0) {
+	/* XXX Could delay raising the error until we fallback, but throwing
+	 * the error here means that we can catch the real culprit.
+	 */
+	status = _cairo_surface_set_error (surface, CAIRO_STATUS_INVALID_MATRIX);
+	return;
+    }
+
     _cairo_surface_begin_modification (surface);
 
     surface->x_fallback_resolution = x_pixels_per_inch;