From a64f41f9bf410e24fe687116ba251b5c5d243830 Mon Sep 17 00:00:00 2001
From: Julius Werner <jwerner@chromium.org>
Date: Fri, 12 May 2017 14:42:58 -0700
Subject: [PATCH] drivers: char: mem: Check for address space wraparound with
 mmap()

commit b299cde245b0b76c977f4291162cf668e087b408 upstream.

/dev/mem currently allows mmap() mappings that wrap around the end of
the physical address space, which should probably be illegal. It
circumvents the existing STRICT_DEVMEM permission check because the loop
immediately terminates (as the start address is already higher than the
end address). On the x86_64 architecture it will then cause a panic
(from the BUG(start >= end) in arch/x86/mm/pat.c:reserve_memtype()).

This patch adds an explicit check to make sure offset + size will not
wrap around in the physical address type.

Signed-off-by: Julius Werner <jwerner@chromium.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
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