net: Prevent infinite while loop in skb_tx_hash()

Drivers call netdev_set_num_tc() and then netdev_set_tc_queue()
to set the queue count and offset for each TC.  So the queue count
and offset for the TCs may be zero for a short period after dev->num_tc
has been set.  If a TX packet is being transmitted at this time in the
code path netdev_pick_tx() -> skb_tx_hash(), skb_tx_hash() may see
nonzero dev->num_tc but zero qcount for the TC.  The while loop that
keeps looping while hash >= qcount will not end.

Fix it by checking the TC's qcount to be nonzero before using it.

Fixes: eadec877ce9c ("net: Add support for subordinate traffic classes to netdev_pick_tx")
Reviewed-by: Andy Gospodarek <gospo@broadcom.com>
Signed-off-by: Michael Chan <michael.chan@broadcom.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/net/core/dev.c b/net/core/dev.c
index 7ee9fecd3affc4cb99eef4dca95a7e8757602545..ea2366497697bb2c80bf3aa1ed9dc143df70c56a 100644 (file)
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -3163,6 +3163,12 @@ static u16 skb_tx_hash(const struct net_device *dev,
 
                qoffset = sb_dev->tc_to_txq[tc].offset;
                qcount = sb_dev->tc_to_txq[tc].count;
+               if (unlikely(!qcount)) {
+                       net_warn_ratelimited("%s: invalid qcount, qoffset %u for tc %u\n",
+                                            sb_dev->name, qoffset, tc);
+                       qoffset = 0;
+                       qcount = dev->real_num_tx_queues;
+               }
        }
 
        if (skb_rx_queue_recorded(skb)) {