linux-kernel - Re: [patch 2/2] fbcmap: integer overflow bug

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Message-ID: <AANLkTin0T5FN6WhUj0csypR=j0UPRbeHN+HC3N9xnk7E@mail.gmail.com>
Date:	Mon, 15 Nov 2010 07:56:05 +0100
From:	Geert Uytterhoeven <geert@...ux-m68k.org>
To:	Paul Mundt <lethal@...ux-sh.org>
Cc:	Dan Carpenter <error27@...il.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux-fbdev@...r.kernel.org, linux-kernel@...r.kernel.org,
	kernel-janitors@...r.kernel.org
Subject: Re: [patch 2/2] fbcmap: integer overflow bug

On Mon, Nov 15, 2010 at 05:48, Paul Mundt <lethal@...ux-sh.org> wrote:
> On Sat, Nov 13, 2010 at 01:07:18PM +0300, Dan Carpenter wrote:
>> @@ -256,8 +264,12 @@ int fb_set_user_cmap(struct fb_cmap_user *cmap, struct fb_info *info)
>>       int rc, size = cmap->len * sizeof(u16);
>>       struct fb_cmap umap;
>>
>> +     if (cmap->len * 2 > INT_MAX)

Isn't that another integer overflow? I.e. should be "if (cmap->len >
INT_MAX / sizeof(u16))" instead?

>> +             return -EINVAL;
>> +
>>       memset(&umap, 0, sizeof(struct fb_cmap));
>> -     rc = fb_alloc_cmap(&umap, cmap->len, cmap->transp != NULL);
>> +     rc = fb_alloc_cmap_gfp(&umap, cmap->len, cmap->transp != NULL,
>> +                             GFP_KERNEL);
>>       if (rc)
>>               return rc;
>>       if (copy_from_user(umap.red, cmap->red, size) ||
>
> This looks reasonable, but it probably makes more sense to use -E2BIG
> for the overflow case (as other cases are doing already), and also just
> to check size directly rather than open-coding the * 2.

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
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