linux-kernel - [PATCH v2 5/5] mremap: simplify the "overlap" check in mremap

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Date:	Thu, 2 Jul 2015 01:03:14 +0200
From:	Oleg Nesterov <oleg@...hat.com>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	Benjamin LaHaise <bcrl@...ck.org>,
	David Rientjes <rientjes@...gle.com>,
	Hugh Dickins <hughd@...gle.com>,
	Jeff Moyer <jmoyer@...hat.com>,
	Kirill Shutemov <kirill.shutemov@...ux.intel.com>,
	Pavel Emelyanov <xemul@...allels.com>,
	linux-kernel@...r.kernel.org
Subject: [PATCH v2 5/5] mremap: simplify the "overlap" check in mremap_to()

Minor, but this check is overcomplicated. Two half-intervals do NOT
overlap if END1 <= START2 || END2 <= START1, mremap_to() just needs
to negate this check.

Signed-off-by: Oleg Nesterov <oleg@...hat.com>
Acked-by: David Rientjes <rientjes@...gle.com>
---
 mm/mremap.c |    9 ++-------
 1 files changed, 2 insertions(+), 7 deletions(-)

diff --git a/mm/mremap.c b/mm/mremap.c
index d3f42be..5a71cce 100644
--- a/mm/mremap.c
+++ b/mm/mremap.c
@@ -407,13 +407,8 @@ static unsigned long mremap_to(unsigned long addr, unsigned long old_len,
 	if (new_len > TASK_SIZE || new_addr > TASK_SIZE - new_len)
 		goto out;
 
-	/* Check if the location we're moving into overlaps the
-	 * old location at all, and fail if it does.
-	 */
-	if ((new_addr <= addr) && (new_addr+new_len) > addr)
-		goto out;
-
-	if ((addr <= new_addr) && (addr+old_len) > new_addr)
+	/* Ensure the old/new locations do not overlap */
+	if (addr + old_len > new_addr && new_addr + new_len > addr)
 		goto out;
 
 	ret = do_munmap(mm, new_addr, new_len);
-- 
1.5.5.1

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