Re: [PATCH] Fix nasty 32-bit overflow bug in buffer i/o code.

From: Anton Altaparmakov
Date: Mon Sep 22 2014 - 11:30:07 EST

Hi Linus,

On 22 Sep 2014, at 16:18, Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx> wrote:
> On Sun, Sep 21, 2014 at 5:53 PM, Anton Altaparmakov <aia21@xxxxxxxxx> 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,


> Linus
> <patch.diff>

Anton Altaparmakov <aia21 at> (replace at with @)
University of Cambridge Information Services, Roger Needham Building
7 JJ Thomson Avenue, Cambridge, CB3 0RB, UK

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