linux-kernel - Re: [PATCH] Fix crash in viafb due to 4k stack overflow

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Date:	Wed, 12 Nov 2008 15:01:04 -0800
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Bruno Prémont <bonbons@...ux-vserver.org>
Cc:	arjan@...radead.org, JosephChan@....com.tw,
	linux-fbdev-devel@...ts.sourceforge.net,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] Fix crash in viafb due to 4k stack overflow

On Mon, 10 Nov 2008 22:00:46 +0100
Bruno Pr__mont <bonbons@...ux-vserver.org> wrote:

> During conversion of viafb_ioctl() I noticed the following:
> 
> Those two cases just copy_from_user and do nothing with copied data,
> incomplete implementation?:
>         case VIAFB_SET_PANEL_POSITION:
>                 if (copy_from_user(&u.panel_pos_size_para, argp,
>                                    sizeof(u.panel_pos_size_para)))
>                         return -EFAULT;
>                 break;
>         case VIAFB_SET_PANEL_SIZE:
>                 if (copy_from_user(&u.panel_pos_size_para, argp,
>                                    sizeof(u.panel_pos_size_para)))
>                         return -EFAULT;
>                 break;
> 
> Handling of GET/SET GAMMA looks buggy:
> In each case 256*4 bytes are allocated but only 4 bytes (size of pointer)
> are copied to/from userspace though viafb_(get|set)_gamma_table() operates
> on the full 256 elements...
>         case VIAFB_SET_GAMMA_LUT:
>                 viafb_gamma_table = kmalloc(256 * sizeof(u32), GFP_KERNEL);
>                 if (!viafb_gamma_table)
>                         return -ENOMEM;
>                 if (copy_from_user(viafb_gamma_table, argp,
>                                 sizeof(viafb_gamma_table))) {
>                         kfree(viafb_gamma_table);
>                         return -EFAULT;
>                 }
>                 viafb_set_gamma_table(viafb_bpp, viafb_gamma_table);
>                 kfree(viafb_gamma_table);
>                 break;
> 
>         case VIAFB_GET_GAMMA_LUT:
>                 viafb_gamma_table = kmalloc(256 * sizeof(u32), GFP_KERNEL);
>                 if (!viafb_gamma_table)
>                         return -ENOMEM;
>                 viafb_get_gamma_table(viafb_gamma_table);
>                 if (copy_to_user(argp, viafb_gamma_table,
>                         sizeof(viafb_gamma_table))) {
>                         kfree(viafb_gamma_table);
>                         return -EFAULT;
>                 }
>                 kfree(viafb_gamma_table);
>                 break;
> 
> I don't know if there is a userspace app that uses these VIA IOCTLs...
> so the ioctl part is just compile-tested.
> After checking, fbset just uses some generic framebuffer IOCTLs outside
> of viafb's scope, thus not passing through viafb_ioctl().
> 
> 
> 
> ---
> --- linux-2.6.28-rc3/drivers/video/via/viafbdev.c.orig	2008-11-09 19:36:47.000000000 +0100
> +++ linux-2.6.28-rc3/drivers/video/via/viafbdev.c	2008-11-10 20:50:32.000000000 +0100

hm, OK, I dropped the old patch and merged this one.

It'd be nice to have it runtime tested and reviewed by Joseph, but we
haven't heard from him yet.  viafb might be 8k-stacks-only in 2.6.27,
which would be bad.

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