linux-kernel - [PATCH] ceph: fix overflow check in build_snap

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Date:	Thu, 16 Feb 2012 11:56:29 -0500
From:	Xi Wang <xi.wang@...il.com>
To:	Sage Weil <sage@...dream.net>
Cc:	ceph-devel@...r.kernel.org, linux-kernel@...r.kernel.org,
	Xi Wang <xi.wang@...il.com>
Subject: [PATCH] ceph: fix overflow check in build_snap_context()

The overflow check for a + n * b should be (n > (ULONG_MAX - a) / b),
rather than (n > ULONG_MAX / b - a).

Signed-off-by: Xi Wang <xi.wang@...il.com>
---
 fs/ceph/snap.c |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)

diff --git a/fs/ceph/snap.c b/fs/ceph/snap.c
index a559c80..f04c096 100644
--- a/fs/ceph/snap.c
+++ b/fs/ceph/snap.c
@@ -331,7 +331,7 @@ static int build_snap_context(struct ceph_snap_realm *realm)
 
 	/* alloc new snap context */
 	err = -ENOMEM;
-	if (num > ULONG_MAX / sizeof(u64) - sizeof(*snapc))
+	if (num > (ULONG_MAX - sizeof(*snapc)) / sizeof(u64))
 		goto fail;
 	snapc = kzalloc(sizeof(*snapc) + num*sizeof(u64), GFP_NOFS);
 	if (!snapc)
-- 
1.7.5.4

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