linux-kernel - [PATCH 3.2 056/106] drivers: char: mem: Fix wraparound check to allow mappings up to the end

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Date:   Sat, 09 Sep 2017 22:47:39 +0100
From:   Ben Hutchings <ben@...adent.org.uk>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
CC:     akpm@...ux-foundation.org,
        "Greg Kroah-Hartman" <gregkh@...uxfoundation.org>,
        "Nico Huber" <nico.h@....de>,
        "Julius Werner" <jwerner@...omium.org>
Subject: [PATCH 3.2 056/106] drivers: char: mem: Fix wraparound check to
 allow mappings up to the end

3.2.93-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Julius Werner <jwerner@...omium.org>

commit 32829da54d9368103a2f03269a5120aa9ee4d5da upstream.

A recent fix to /dev/mem prevents mappings from wrapping around the end
of physical address space. However, the check was written in a way that
also prevents a mapping reaching just up to the end of physical address
space, which may be a valid use case (especially on 32-bit systems).
This patch fixes it by checking the last mapped address (instead of the
first address behind that) for overflow.

Fixes: b299cde245 ("drivers: char: mem: Check for address space wraparound with mmap()")
Reported-by: Nico Huber <nico.h@....de>
Signed-off-by: Julius Werner <jwerner@...omium.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Signed-off-by: Ben Hutchings <ben@...adent.org.uk>
---
 drivers/char/mem.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/drivers/char/mem.c
+++ b/drivers/char/mem.c
@@ -325,7 +325,7 @@ static int mmap_mem(struct file *file, s
 	phys_addr_t offset = (phys_addr_t)vma->vm_pgoff << PAGE_SHIFT;
 
 	/* It's illegal to wrap around the end of the physical address space. */
-	if (offset + (phys_addr_t)size < offset)
+	if (offset + (phys_addr_t)size - 1 < offset)
 		return -EINVAL;
 
 	if (!valid_mmap_phys_addr_range(vma->vm_pgoff, size))