net: netprio: fix cgrp create and write priomap race

A race exists where creating cgroups and also updating the priomap
may result in losing a priomap update. This is because priomap
writers are not protected by rtnl_lock.

Move priority writer into rtnl_lock()/rtnl_unlock().

CC: Neil Horman <nhorman@tuxdriver.com>
Reported-by: Al Viro <viro@ZenIV.linux.org.uk>
Signed-off-by: John Fastabend <john.r.fastabend@intel.com>
Acked-by: Neil Horman <nhorman@tuxdriver.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/net/core/netprio_cgroup.c b/net/core/netprio_cgroup.c
index f65dba3..c75e3f9 100644 (file)
--- a/net/core/netprio_cgroup.c
+++ b/net/core/netprio_cgroup.c
@@ -101,12 +101,10 @@ static int write_update_netdev_table(struct net_device *dev)
        u32 max_len;
        struct netprio_map *map;
 
-       rtnl_lock();
        max_len = atomic_read(&max_prioidx) + 1;
        map = rtnl_dereference(dev->priomap);
        if (!map || map->priomap_len < max_len)
                ret = extend_netdev_table(dev, max_len);
-       rtnl_unlock();
 
        return ret;
 }
@@ -256,17 +254,17 @@ static int write_priomap(struct cgroup *cgrp, struct cftype *cft,
        if (!dev)
                goto out_free_devname;
 
+       rtnl_lock();
        ret = write_update_netdev_table(dev);
        if (ret < 0)
                goto out_put_dev;
 
-       rcu_read_lock();
-       map = rcu_dereference(dev->priomap);
+       map = rtnl_dereference(dev->priomap);
        if (map)
                map->priomap[prioidx] = priority;
-       rcu_read_unlock();
 
 out_put_dev:
+       rtnl_unlock();
        dev_put(dev);
 
 out_free_devname: