[PATCH 5.10 52/77] net: Prevent infinite while loop in skb_tx_hash()

Greg Kroah-Hartman
2021-11-01T09:36:20Z

From: Michael Chan <michael.chan@broadcom.com>

commit 0c57eeecc559ca6bc18b8c4e2808bc78dbe769b0 upstream.

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>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
net/core/dev.c | 6 ++++++
1 file changed, 6 insertions(+)

--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -3171,6 +3171,12 @@ static u16 skb_tx_hash(const struct net_

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)) {