Re: [PATCH] ui/gtk: fix NULL pointer dereference

[Akihiko Odaki]

2021年3月8日(月) 22:38 Peter Maydell <peter.maydell@linaro.org>:
>
> The online defect viewer is a bit better for showing why it thought
> something was an issue. In this case we have at the top of the function:
>
>     trace_gd_switch(vc->label,
>                     surface ? surface_width(surface)  : 0,
>                     surface ? surface_height(surface) : 0);
>
> which tests whether surface is NULL, implying that sometimes it is.
>
> Then later we have:
>     if (vc->gfx.ds && surface &&
>
> also checking surface for NULL-ness.
>
> Finally we have:
>     if (surface->format == PIXMAN_x8r8g8b8) {
>
> which dereferences surface without checking if it's NULL.
>
> So there is definitely a bug here:
> (1) either surface can never be NULL, and all the places where
> the function is testing for NULL-ness are wrong and need to be removed
> (2) or surface can be NULL, and we should check here too
>
> Coverity can't tell us which of the two possibilities is right, of course.
>
> thanks
> -- PMM

c821a58ee7 ("ui/console: Pass placeholder surface to display")
intended to eliminate the possibility that surface is NULL, so (1) is
the case. I am preparing a patch to remove NULL checks.

Thanks,
Akihiko Odaki