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net-sysfs: Add rtnl locking for getting Tx queue traffic class
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In order to access the suboordinate dev for a device we should be holding
the rtnl_lock when outside of the transmit path. The existing code was not
doing that for the sysfs dump function and as a result we were open to a
possible race.

To resolve that take the rtnl lock prior to accessing the sb_dev field of
the Tx queue and release it after we have retrieved the tc for the queue.

Signed-off-by: Alexander Duyck <alexanderduyck@fb.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
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Alexander Duyck authored and David S. Miller committed Feb 8, 2021
1 parent 796c901 commit b2f1756
Showing 1 changed file with 10 additions and 3 deletions.
13 changes: 10 additions & 3 deletions net/core/net-sysfs.c
Original file line number Diff line number Diff line change
Expand Up @@ -1136,18 +1136,25 @@ static ssize_t traffic_class_show(struct netdev_queue *queue,
char *buf)
{
struct net_device *dev = queue->dev;
int num_tc, tc;
int index;
int tc;

if (!netif_is_multiqueue(dev))
return -ENOENT;

if (!rtnl_trylock())
return restart_syscall();

index = get_netdev_queue_index(queue);

/* If queue belongs to subordinate dev use its TC mapping */
dev = netdev_get_tx_queue(dev, index)->sb_dev ? : dev;

num_tc = dev->num_tc;
tc = netdev_txq_to_tc(dev, index);

rtnl_unlock();

if (tc < 0)
return -EINVAL;

Expand All @@ -1158,8 +1165,8 @@ static ssize_t traffic_class_show(struct netdev_queue *queue,
* belongs to the root device it will be reported with just the
* traffic class, so just "0" for TC 0 for example.
*/
return dev->num_tc < 0 ? sprintf(buf, "%d%d\n", tc, dev->num_tc) :
sprintf(buf, "%d\n", tc);
return num_tc < 0 ? sprintf(buf, "%d%d\n", tc, num_tc) :
sprintf(buf, "%d\n", tc);
}

#ifdef CONFIG_XPS
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