Re: [BUG] SLOB's krealloc() seems bust

From: Pekka Enberg
Date: Tue Oct 07 2008 - 12:57:44 EST


Hi Matt,

On Tue, Oct 7, 2008 at 7:37 PM, Matt Mackall <mpm@xxxxxxxxxxx> wrote:
> SLOB: fix bogus ksize calculation
>
> SLOB's ksize calculation was braindamaged and generally harmlessly
> underreported the allocation size. But for very small buffers, it could
> in fact overreport them, leading code depending on krealloc to overrun
> the allocation and trample other data.
>
> Signed-off-by: Matt Mackall <mpm@xxxxxxxxxxx>
> Tested-by: Peter Zijlstra <a.p.zijlstra@xxxxxxxxx>
>
> diff -r 5e32b09a1b2b mm/slob.c
> --- a/mm/slob.c Fri Oct 03 14:04:43 2008 -0500
> +++ b/mm/slob.c Tue Oct 07 11:27:47 2008 -0500
> @@ -515,7 +515,7 @@
>
> sp = (struct slob_page *)virt_to_page(block);
> if (slob_page(sp))
> - return ((slob_t *)block - 1)->units + SLOB_UNIT;
> + return (((slob_t *)block - 1)->units - 1) * SLOB_UNIT;

Hmm. I don't understand why we do the "minus one" thing here. Aren't
we underestimating the size now? Side note, why aren't we using
slob_units() here?

> else
> return sp->page.private;
> }
>
>
>
>
>
> --
> Mathematics is the supreme nostalgia of our time.
>
> --
> To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
> the body of a message to majordomo@xxxxxxxxxxxxxxx
> More majordomo info at http://vger.kernel.org/majordomo-info.html
> Please read the FAQ at http://www.tux.org/lkml/
>
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/