net-sysfs: take the rtnl lock when accessing xps_cpus_map and num_tc

Accesses to dev->xps_cpus_map (when using dev->num_tc) should be
protected by the rtnl lock, like we do for netif_set_xps_queue. I didn't
see an actual bug being triggered, but let's be safe here and take the
rtnl lock while accessing the map in sysfs.

Fixes: 184c449f91fe ("net: Add support for XPS with QoS via traffic classes")
Signed-off-by: Antoine Tenart <atenart@kernel.org>
Reviewed-by: Alexander Duyck <alexanderduyck@fb.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

diff --git a/net/core/net-sysfs.c b/net/core/net-sysfs.c
index 7cc15de..65886bf 100644 (file)
--- a/net/core/net-sysfs.c
+++ b/net/core/net-sysfs.c
@@ -1317,8 +1317,8 @@ static const struct attribute_group dql_group = {
 static ssize_t xps_cpus_show(struct netdev_queue *queue,
                             char *buf)
 {
+       int cpu, len, ret, num_tc = 1, tc = 0;
        struct net_device *dev = queue->dev;
-       int cpu, len, num_tc = 1, tc = 0;
        struct xps_dev_maps *dev_maps;
        cpumask_var_t mask;
        unsigned long index;
@@ -1328,22 +1328,31 @@ static ssize_t xps_cpus_show(struct netdev_queue *queue,
 
        index = get_netdev_queue_index(queue);
 
+       if (!rtnl_trylock())
+               return restart_syscall();
+
        if (dev->num_tc) {
                /* Do not allow XPS on subordinate device directly */
                num_tc = dev->num_tc;
-               if (num_tc < 0)
-                       return -EINVAL;
+               if (num_tc < 0) {
+                       ret = -EINVAL;
+                       goto err_rtnl_unlock;
+               }
 
                /* If queue belongs to subordinate dev use its map */
                dev = netdev_get_tx_queue(dev, index)->sb_dev ? : dev;
 
                tc = netdev_txq_to_tc(dev, index);
-               if (tc < 0)
-                       return -EINVAL;
+               if (tc < 0) {
+                       ret = -EINVAL;
+                       goto err_rtnl_unlock;
+               }
        }
 
-       if (!zalloc_cpumask_var(&mask, GFP_KERNEL))
-               return -ENOMEM;
+       if (!zalloc_cpumask_var(&mask, GFP_KERNEL)) {
+               ret = -ENOMEM;
+               goto err_rtnl_unlock;
+       }
 
        rcu_read_lock();
        dev_maps = rcu_dereference(dev->xps_cpus_map);
@@ -1366,9 +1375,15 @@ static ssize_t xps_cpus_show(struct netdev_queue *queue,
        }
        rcu_read_unlock();
 
+       rtnl_unlock();
+
        len = snprintf(buf, PAGE_SIZE, "%*pb\n", cpumask_pr_args(mask));
        free_cpumask_var(mask);
        return len < PAGE_SIZE ? len : -EINVAL;
+
+err_rtnl_unlock:
+       rtnl_unlock();
+       return ret;
 }
 
 static ssize_t xps_cpus_store(struct netdev_queue *queue,