linux-kernel - [PATCH] mm/memblock.c: Correctly check whether to trim a block

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Date:	Wed, 28 Mar 2012 19:25:58 -0700
From:	Laura Abbott <lauraa@...eaurora.org>
To:	linux-mm@...ck.org, benh@...nel.crashing.org, yinghai@...nel.org
Cc:	linux-kernel@...r.kernel.org, linux-arm-msm@...r.kernel.org,
	Laura Abbott <lauraa@...eaurora.org>
Subject: [PATCH] mm/memblock.c: Correctly check whether to trim a block

Currently in __memblock_remove, the check to trim the top of
a block off only checks if the requested base is less than the
memblock end. If the end of the requested region is equal to
the start of a memblock, this will incorrectly try to remove
the block, possibly causing an integer underflow:

   ---------------------------------------
   |                    |                |
   |                    |                |
  base              end = rgn->base    rend

An additional check is needed to see if the end of the requested
region is greater than the memblock region:

   ----------------------
   |                     |
   |                     |
  rgn->base    base     rend      end
                |                  |
                |                  |
                --------------------

Signed-off-by: Laura Abbott <lauraa@...eaurora.org>
---
 mm/memblock.c |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)

diff --git a/mm/memblock.c b/mm/memblock.c
index 5338237..e174ee0 100644
--- a/mm/memblock.c
+++ b/mm/memblock.c
@@ -459,7 +459,7 @@ static long __init_memblock __memblock_remove(struct memblock_type *type,
 		}
 
 		/* And check if we need to trim the top of a block */
-		if (base < rend)
+		if (base < rend && end > rend)
 			rgn->size -= rend - base;
 
 	}
-- 
1.7.8.3

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