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>

1 files changed, 3 insertions, 5 deletions

diff --git a/net/core/netprio_cgroup.c b/net/core/netprio_cgroup.c
index f65dba3afd99..c75e3f9d060f 100644
--- 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: