[PATCH 3.4.y 1/3] cgroup: fix panic in netprio_cgroup

[Li Zefan <lizefan@huawei.com>]

From: Gao feng <gaofeng@cn.fujitsu.com>

commit b761c9b1f4f69eb53fb6147547a1ab25237a93b3 upstream.

we set max_prioidx to the first zero bit index of prioidx_map in
function get_prioidx.

So when we delete the low index netprio cgroup and adding a new
netprio cgroup again,the max_prioidx will be set to the low index.

when we set the high index cgroup's net_prio.ifpriomap,the function
write_priomap will call update_netdev_tables to alloc memory which
size is sizeof(struct netprio_map) + sizeof(u32) * (max_prioidx + 1),
so the size of array that map->priomap point to is max_prioidx +1,
which is low than what we actually need.

fix this by adding check in get_prioidx,only set max_prioidx when
max_prioidx low than the new prioidx.

Signed-off-by: Gao feng <gaofeng@cn.fujitsu.com>
Acked-by: Neil Horman <nhorman@tuxdriver.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Li Zefan <lizefan@huawei.com>
---
 net/core/netprio_cgroup.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/net/core/netprio_cgroup.c b/net/core/netprio_cgroup.c
index ba6900f..4435296 100644
--- a/net/core/netprio_cgroup.c
+++ b/net/core/netprio_cgroup.c
@@ -62,8 +62,9 @@ static int get_prioidx(u32 *prio)
 		return -ENOSPC;
 	}
 	set_bit(prioidx, prioidx_map);
+	if (atomic_read(&max_prioidx) < prioidx)
+		atomic_set(&max_prioidx, prioidx);
 	spin_unlock_irqrestore(&prioidx_map_lock, flags);
-	atomic_set(&max_prioidx, prioidx);
 	*prio = prioidx;
 	return 0;
 }
-- 
1.8.0.2