linux-kernel - [PATCH v2] mtd: blktrans: fix multiplication overflow

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Date:	Fri, 11 Sep 2015 21:41:47 +0800
From:	Peng Fan <van.freenix@...il.com>
To:	linux-mtd@...ts.infradead.org, linux-kernel@...r.kernel.org,
	computersforpeace@...il.com
Cc:	van.freenix@...il.com, David Woodhouse <dwmw2@...radead.org>
Subject: [PATCH v2] mtd: blktrans: fix multiplication overflow

In drivers/mtd/mtd_blkdevs.c:
406	set_capacity(gd, (new->size * tr->blksize) >> 9);
The type of new->size is unsigned long and the type of tr->blksize is int,
the result of 'new->size * tr->blksize' may exceed ULONG_MAX on 32bit
machines.

I use nand chip MT29F32G08CBADBWP which is 4GB and the parameters passed
to kernel is 'mtdparts=gpmi-nand:-(user)', the whole nand chip will be
treated as a 4GB mtd partition. new->size is 0x800000 and tr->blksize is
0x200, 'new->size * tr->blksize' however is 0. This is what we do not want
to see.

Using type cast u64 to fix the multiplication overflow issue.

Signed-off-by: Peng Fan <van.freenix@...il.com>
Cc: David Woodhouse <dwmw2@...radead.org>
Cc: Brian Norris <computersforpeace@...il.com>
---

Changes V2:
 use type cast to avoid build break for platforms which does not support 64 bit multilplication.

 drivers/mtd/mtd_blkdevs.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/mtd/mtd_blkdevs.c b/drivers/mtd/mtd_blkdevs.c
index 44dc965..cb47d79 100644
--- a/drivers/mtd/mtd_blkdevs.c
+++ b/drivers/mtd/mtd_blkdevs.c
@@ -399,7 +399,7 @@ int add_mtd_blktrans_dev(struct mtd_blktrans_dev *new)
 		snprintf(gd->disk_name, sizeof(gd->disk_name),
 			 "%s%d", tr->name, new->devnum);

-	set_capacity(gd, (new->size * tr->blksize) >> 9);
+	set_capacity(gd, ((u64)new->size * tr->blksize) >> 9);

 	/* Create the request queue */
 	spin_lock_init(&new->queue_lock);
-- 
1.8.4

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