[Qemu-devel] [PATCH] ui/virtio-gpu: add and use qemu_create_displaysurface_pixman

[Gerd Hoffmann <kraxel@redhat.com>]

Add a the new qemu_create_displaysurface_pixman function, to create
a DisplaySurface backed by an existing pixman image.  In that case
there is no need to create a new pixman image pointing to the same
backing storage.  We can just use the existing image directly.

This does not only simplify things a bit, but most importantly it
gets the reference counting right, so the backing storage for the
pixman image wouldn't be released underneath us.

Use new function in virtio-gpu, where using it actually fixes
use-after-free crashes.

Cc: qemu-stable@nongnu.org
Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
---
 hw/display/virtio-gpu.c |  5 +----
 include/ui/console.h    |  1 +
 trace-events            |  1 +
 ui/console.c            | 11 +++++++++++
 4 files changed, 14 insertions(+), 4 deletions(-)

diff --git a/hw/display/virtio-gpu.c b/hw/display/virtio-gpu.c
index ddf3bfb..095d7ff 100644
--- a/hw/display/virtio-gpu.c
+++ b/hw/display/virtio-gpu.c
@@ -572,10 +572,7 @@ static void virtio_gpu_set_scanout(VirtIOGPU *g,
         scanout->width != ss.r.width ||
         scanout->height != ss.r.height) {
         /* realloc the surface ptr */
-        scanout->ds = qemu_create_displaysurface_from
-            (ss.r.width, ss.r.height, format,
-             pixman_image_get_stride(res->image),
-             (uint8_t *)pixman_image_get_data(res->image) + offset);
+        scanout->ds = qemu_create_displaysurface_pixman(res->image);
         if (!scanout->ds) {
             cmd->error = VIRTIO_GPU_RESP_ERR_UNSPEC;
             return;
diff --git a/include/ui/console.h b/include/ui/console.h
index eb9419d..d5a88d9 100644
--- a/include/ui/console.h
+++ b/include/ui/console.h
@@ -234,6 +234,7 @@ DisplayState *init_displaystate(void);
 DisplaySurface *qemu_create_displaysurface_from(int width, int height,
                                                 pixman_format_code_t format,
                                                 int linesize, uint8_t *data);
+DisplaySurface *qemu_create_displaysurface_pixman(pixman_image_t *image);
 DisplaySurface *qemu_create_displaysurface_guestmem(int width, int height,
                                                     pixman_format_code_t format,
                                                     int linesize,
diff --git a/trace-events b/trace-events
index 996a77f..8350743 100644
--- a/trace-events
+++ b/trace-events
@@ -1161,6 +1161,7 @@ console_select(int nr) "%d"
 console_refresh(int interval) "interval %d ms"
 displaysurface_create(void *display_surface, int w, int h) "surface=%p, %dx%d"
 displaysurface_create_from(void *display_surface, int w, int h, uint32_t format) "surface=%p, %dx%d, format 0x%x"
+displaysurface_create_pixman(void *display_surface) "surface=%p"
 displaysurface_free(void *display_surface) "surface=%p"
 displaychangelistener_register(void *dcl, const char *name) "%p [ %s ]"
 displaychangelistener_unregister(void *dcl, const char *name) "%p [ %s ]"
diff --git a/ui/console.c b/ui/console.c
index 1fd4ea4..bf38579 100644
--- a/ui/console.c
+++ b/ui/console.c
@@ -1292,6 +1292,17 @@ DisplaySurface *qemu_create_displaysurface_from(int width, int height,
     return surface;
 }
 
+DisplaySurface *qemu_create_displaysurface_pixman(pixman_image_t *image)
+{
+    DisplaySurface *surface = g_new0(DisplaySurface, 1);
+
+    trace_displaysurface_create_pixman(surface);
+    surface->format = pixman_image_get_format(image);
+    surface->image = pixman_image_ref(image);
+
+    return surface;
+}
+
 static void qemu_unmap_displaysurface_guestmem(pixman_image_t *image,
                                                void *unused)
 {
-- 
1.8.3.1