[PATCH] Fix bound checking in do_mmap_pgoff()

[Benjamin Herrenschmidt <benh@kernel.crashing.org>]

Hi !

A small issue has been forever in do_mmap_pgoff() in the boundary checking
in the sense that it won't let you mmap with offset+len enclosing the last
page of the "address space". For example, an mmap of /dev/mem won't let you
map the last page of the physical address space (which I need for a ROM dump
tool on pmac). This fixes it:

Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>

===== mm/mmap.c 1.144 vs edited =====
--- 1.144/mm/mmap.c	2004-09-03 19:08:17 +10:00
+++ edited/mm/mmap.c	2004-09-19 18:04:34 +10:00
@@ -801,7 +801,7 @@
 		return -EINVAL;
 
 	/* offset overflow? */
-	if ((pgoff + (len >> PAGE_SHIFT)) < pgoff)
+	if ((pgoff + (len >> PAGE_SHIFT) - 1) < pgoff)
 		return -EINVAL;
 
 	/* Too many mappings? */