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

["Reese Faucette" <reesefaucette@gmail.com>]

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? */