linux-kernel - Re: [PATCH] overflow check calculation in mm/mmap.c is incorrect linux-3.12.38

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Message-Id: <20150507165356.6efa045e5e1179ef4f46fdb9@linux-foundation.org>
Date:	Thu, 7 May 2015 16:53:56 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	"Reese Faucette" <reesefaucette@...il.com>
Cc:	<linux-kernel@...r.kernel.org>, <alan@...rguk.ukuu.org.uk>
Subject: Re: [PATCH] overflow check calculation in mm/mmap.c is incorrect
 linux-3.12.38

On Wed, 29 Apr 2015 22:14:19 -0700 "Reese Faucette" <reesefaucette@...il.com> wrote:

> When checking for overflow, the code in mm/mmap.c compares the first byte
> *after* the end of mapped region to the start of the region instead of the
> last byte of the mapped region.  This prevents mapping a region which abuts
> the end of physical space, as mmap() incorrectly rejects the region with
> -EOVERFLOW, because pgoff + (len >> PAGE_SHIFT) will be 0, which is < pgoff.
> -reese
> 
> Reese Faucette
> Cisco Systems, Inc.
> 
> ====================================================
> --- mm/mmap.c
> +++ mm/mmap.c
> @@ -1241,7 +1241,7 @@
>                 return -ENOMEM;
> 
>         /* offset overflow? */
> -       if ((pgoff + (len >> PAGE_SHIFT)) < pgoff)
> +       if ((pgoff + (len >> PAGE_SHIFT) - 1) < pgoff)
>                 return -EOVERFLOW;
> 
>         /* Too many mappings? */

Looks right.

Please send a Signed-off-by: for this patch, as per
Documentation/SubmittingPatches, section 11.  Please also let me know
whether the authorship should be you@...il.com or some Cisco address,
as people often prefer.
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