linux-kernel - Re: [PATCH] m68k: fix find

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Date:	Wed, 30 Mar 2011 20:02:50 +0200
From:	Geert Uytterhoeven <geert@...ux-m68k.org>
To:	Akinobu Mita <akinobu.mita@...il.com>,
	Andreas Schwab <schwab@...ux-m68k.org>
Cc:	linux-kernel@...r.kernel.org, akpm@...ux-foundation.org,
	Roman Zippel <zippel@...ux-m68k.org>,
	linux-m68k@...r.kernel.org,
	Michael Schmitz <schmitzmic@...glemail.com>
Subject: Re: [PATCH] m68k: fix find_next bitops

On Fri, Mar 25, 2011 at 12:00, Akinobu Mita <akinobu.mita@...il.com> wrote:
> find_next bitops on m68k (find_next_zero_bit, find_next_bit, and
> find_next_bit_le) may cause out of bounds memory access
> when the bitmap size in bits % 32 != 0 and offset (the bitnumber
> to start searching at) is very close to the bitmap size.
>
> For example,
>
>       unsigned long bitmap[2] = { 0, 0 };
>       find_next_bit(bitmap, 63, 62);
>
> 1. find_next_bit() tries to find any set bits in bitmap[1],
>   but no bits set.
>
> 2. Then find_first_bit(bimap + 2, -1)
>
> 3. Unfortunately find_fist_bit() takes unsigned int as the size argument.
>
> 4. find_first_bit will access bitmap[2~] until it find any set bits.
>
> This switches find_next bitops to use generic implementation of
> find bitops to fix the problem.

Andreas, do you think it's worth keeping (and fixing) the m68k "optimized"
versions?

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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