linux-kernel - Re: [PATCH 4/7] video: fbdev: vt8623fb: Error out if 'pixclock' equals zero

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Date:   Mon, 4 Apr 2022 13:47:24 +0200
From:   Geert Uytterhoeven <geert@...ux-m68k.org>
To:     Zheyu Ma <zheyuma97@...il.com>
Cc:     Helge Deller <deller@....de>,
        Linux Fbdev development list <linux-fbdev@...r.kernel.org>,
        DRI Development <dri-devel@...ts.freedesktop.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 4/7] video: fbdev: vt8623fb: Error out if 'pixclock'
 equals zero

Hi Zheyu,

On Mon, Apr 4, 2022 at 1:07 PM Zheyu Ma <zheyuma97@...il.com> wrote:
> The userspace program could pass any values to the driver through
> ioctl() interface. If the driver doesn't check the value of 'pixclock',
> it may cause divide error.
>
> Fix this by checking whether 'pixclock' is zero in the function
> vt8623fb_check_var().
>
> The following log reveals it:
>
> [   47.778727] divide error: 0000 [#1] PREEMPT SMP KASAN PTI
> [   47.778803] RIP: 0010:vt8623fb_set_par+0xecd/0x2210
> [   47.778870] Call Trace:
> [   47.778872]  <TASK>
> [   47.778909]  fb_set_var+0x604/0xeb0
> [   47.778995]  do_fb_ioctl+0x234/0x670
> [   47.779041]  fb_ioctl+0xdd/0x130
> [   47.779048]  do_syscall_64+0x3b/0x90
>
> Signed-off-by: Zheyu Ma <zheyuma97@...il.com>

Thanks for your patch!

> --- a/drivers/video/fbdev/vt8623fb.c
> +++ b/drivers/video/fbdev/vt8623fb.c
> @@ -321,6 +321,9 @@ static int vt8623fb_check_var(struct fb_var_screeninfo *var, struct fb_info *inf
>  {
>         int rv, mem, step;
>
> +       if (!var->pixclock)
> +               return -EINVAL;
> +

When passed an invalid value, .check_var() is supposed to
round up the invalid to a valid value, if possible.

>         /* Find appropriate format */
>         rv = svga_match_format (vt8623fb_formats, var, NULL);
>         if (rv < 0)

Gr{oetje,eeting}s,

                        Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@...ux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds