linux-kernel - Re: [PATCH] x86: simplefb: avoid overflow

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Message-ID: <CANq1E4Tco9K1zeL2d7MhBQ=UjHFOktrrR8GHp8cJm3V6CTqf0g@mail.gmail.com>
Date:	Fri, 6 Sep 2013 11:55:29 +0200
From:	David Herrmann <dh.herrmann@...il.com>
To:	Tom Gundersen <teg@...m.no>
Cc:	x86@...nel.org, linux-kernel <linux-kernel@...r.kernel.org>,
	Ingo Molnar <mingo@...hat.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	"H. Peter Anvin" <hpa@...or.com>
Subject: Re: [PATCH] x86: simplefb: avoid overflow

Hi

On Fri, Sep 6, 2013 at 11:32 AM, Tom Gundersen <teg@...m.no> wrote:
> lfb_size can easily be say 4M, which would make the bitshit overflow and
> the test fail.
>
> Signed-off-by: Tom Gundersen <teg@...m.no>
> Cc: David Herrmann <dh.herrmann@...il.com>
> Cc: H. Peter Anvin <hpa@...or.com>
> ---
>  arch/x86/kernel/sysfb_simplefb.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/arch/x86/kernel/sysfb_simplefb.c b/arch/x86/kernel/sysfb_simplefb.c
> index 22513e9..fff44a5 100644
> --- a/arch/x86/kernel/sysfb_simplefb.c
> +++ b/arch/x86/kernel/sysfb_simplefb.c
> @@ -72,7 +72,7 @@ __init int create_simplefb(const struct screen_info *si,
>          * the part that is occupied by the framebuffer */
>         len = mode->height * mode->stride;
>         len = PAGE_ALIGN(len);
> -       if (len > si->lfb_size << 16) {
> +       if (len > ((unsigned long) si->lfb_size) << 16) {

Nice catch. vesafb uses "lfb_size * 65535" which causes an implicit
cast. I thought <<16 looks nicer but that doesn't do any implicit
cast..

Nothing crucial, as it only causes the simple-fb conversion to fail.
But would still be good to see in -rc2:
Reviewed-by: David Herrmann <dh.herrmann@...il.com>

Thanks
David

>                 printk(KERN_WARNING "sysfb: VRAM smaller than advertised\n");
>                 return -EINVAL;
>         }
> --
> 1.8.4
>
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