On Mon, Jul 13, 2020 at 02:51:05PM +0200, Philippe Mathieu-Daudé wrote:
> On 7/13/20 2:45 PM, Gerd Hoffmann wrote:
> > Calling ramfb_display_update() might replace the DisplaySurface with the
> > boot display, which in turn will free the currently active
> > DisplaySurface.
> >
> > So clear our DisplaySurface pinter (dpy->region.surface pointer) to (a)
> > avoid use-after-free and (b) force replacing the boot display with the
> > real display when switching back.
> >
> > Signed-off-by: Gerd Hoffmann <kra...@redhat.com>
> > ---
> > hw/vfio/display.c | 1 +
> > 1 file changed, 1 insertion(+)
> >
> > diff --git a/hw/vfio/display.c b/hw/vfio/display.c
> > index a57a22674d62..342054193b3c 100644
> > --- a/hw/vfio/display.c
> > +++ b/hw/vfio/display.c
> > @@ -405,6 +405,7 @@ static void vfio_display_region_update(void *opaque)
> > if (!plane.drm_format || !plane.size) {
> > if (dpy->ramfb) {
> > ramfb_display_update(dpy->con, dpy->ramfb);
> > + dpy->region.surface = NULL;
> > }
> > return;
> > }
> >
>
> More generic fix:
>
> -- >8 --
> --- a/ui/console.c
> +++ b/ui/console.c
> @@ -1580,10 +1580,10 @@ void dpy_gfx_replace_surface(QemuConsole *con,
> DisplaySurface *surface)
> {
> DisplayState *s = con->ds;
> - DisplaySurface *old_surface = con->surface;
> + QemuConsole *old_con = con;
> DisplayChangeListener *dcl;
>
> - assert(old_surface != surface || surface == NULL);
> + assert(con->surface != surface || surface == NULL);
>
> con->surface = surface;
> QLIST_FOREACH(dcl, &s->listeners, next) {
> @@ -1594,7 +1594,8 @@ void dpy_gfx_replace_surface(QemuConsole *con,
> dcl->ops->dpy_gfx_switch(dcl, surface);
> }
> }
> - qemu_free_displaysurface(old_surface);
> + qemu_free_displaysurface(old_con->surface);
> + old_con->surface = NULL;
No.
That doesn't clear VFIODisplay->region.surface, but it sets
QemuConsole->surface to NULL no matter what got passed to
dpy_gfx_replace_surface().
Guesswork based just on the patch chunk doesn't always work,
sometimes you have to consult the source code to see what the
patch actually does ;)
take care,
Gerd
