linux-kernel - Re: [PATCH] fbdev: potential information leak in do_fb

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Message-ID: <87ftj8k1j9.fsf@x220.int.ebiederm.org>
Date:   Thu, 31 Oct 2019 17:12:10 -0500
From:   ebiederm@...ssion.com (Eric W. Biederman)
To:     Joe Perches <joe@...ches.com>
Cc:     Andrea Righi <andrea.righi@...onical.com>,
        Dan Carpenter <dan.carpenter@...cle.com>,
        Bartlomiej Zolnierkiewicz <b.zolnierkie@...sung.com>,
        Daniel Vetter <daniel.vetter@...ll.ch>,
        Sam Ravnborg <sam@...nborg.org>,
        Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
        Peter Rosin <peda@...ntia.se>,
        Gerd Hoffmann <kraxel@...hat.com>,
        dri-devel@...ts.freedesktop.org, linux-fbdev@...r.kernel.org,
        linux-kernel@...r.kernel.org, kernel-janitors@...r.kernel.org,
        security@...nel.org, Kees Cook <keescook@...omium.org>,
        Julia Lawall <Julia.Lawall@...6.fr>
Subject: Re: [PATCH] fbdev: potential information leak in do_fb_ioctl()

Joe Perches <joe@...ches.com> writes:

> On Wed, 2019-10-30 at 21:12 +0100, Andrea Righi wrote:
>> Then memset() + memcpy() is probably the best option,
>> since copying all those fields one by one looks quite ugly to me...
>
> A memset of an automatic before a memcpy to the same
> automatic is unnecessary.

You still need to guarantee that all of the holes in the
structure you are copying are initialized before you copy it.

Otherwise you are just changing which unitialized memory that
is being copied to userspace.

Which is my concern with your very simple suggestion.

Eric