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Subject: Re: [PATCH] Fix nasty 32-bit overflow bug in buffer i/o code.
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From: Anton Altaparmakov <aia21@cam.ac.uk>
In-Reply-To: <CA+55aFyYpe=oyF9yVqF3E6t4ZCpHAdnLj1g36FWUDZydW9mdgQ@mail.gmail.com>
Date: Mon, 22 Sep 2014 16:29:56 +0100
Cc: Andrew Morton <akpm@linux-foundation.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        linux-fsdevel <linux-fsdevel@vger.kernel.org>,
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To: Linus Torvalds <torvalds@linux-foundation.org>
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Hi Linus,

On 22 Sep 2014, at 16:18, Linus Torvalds <torvalds@linux-foundation.org> wrote:
> On Sun, Sep 21, 2014 at 5:53 PM, Anton Altaparmakov <aia21@cam.ac.uk> wrote:
>> 
>> This patch fixes this issue by type casting "index" to sector_t before
>> doing the left shift.
> 
> Ugh. Does the simpler patch to just pass in "block" work as well?

That doesn't work because nothing rounds down "block" to the first block in the page and init_page_buffers() requires "block" to be the first block in the page.

The shift right followed by shift left achieves the "rounding down" required.

You could do "block & ~(sector_t)(size - 1)" instead of "(sector_t)index << sizebits" if you prefer but not sure that is an improvement!

Best regards,

	Anton

>                    Linus
> <patch.diff>


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Anton Altaparmakov <aia21 at cam.ac.uk> (replace at with @)
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