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

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Message-ID: <007301d08304$85881420$90983c60$@gmail.com>
Date:	Wed, 29 Apr 2015 22:14:19 -0700
From:	"Reese Faucette" <reesefaucette@...il.com>
To:	<linux-kernel@...r.kernel.org>
Cc:	<alan@...rguk.ukuu.org.uk>
Subject: [PATCH] overflow check calculation in mm/mmap.c is incorrect linux-3.12.38

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? */

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