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.w...@gmail.com>
Signed-off-by: Sage Weil <s...@newdream.net>
---
 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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