sfc: Fix maximum number of TSO segments and minimum TX queue size

Currently an skb requiring TSO may not fit within a minimum-size TX
queue.  The TX queue selected for the skb may stall and trigger the TX
watchdog repeatedly (since the problem skb will be retried after the
TX reset).  This issue is designated as CVE-2012-3412.

Set the maximum number of TSO segments for our devices to 100.  This
should make no difference to behaviour unless the actual MSS is less
than about 700.  Increase the minimum TX queue size accordingly to
allow for 2 worst-case skbs, so that there will definitely be space
to add an skb after we wake a queue.

To avoid invalidating existing configurations, change
efx_ethtool_set_ringparam() to fix up values that are too small rather
than returning -EINVAL.

Signed-off-by: Ben Hutchings <bhutchings@solarflare.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 11 insertions, 5 deletions

diff --git a/drivers/net/ethernet/sfc/ethtool.c b/drivers/net/ethernet/sfc/ethtool.c
index 10536f93b561..8cba2df82b18 100644
--- a/drivers/net/ethernet/sfc/ethtool.c
+++ b/drivers/net/ethernet/sfc/ethtool.c
@@ -680,21 +680,27 @@ static int efx_ethtool_set_ringparam(struct net_device *net_dev,
 				     struct ethtool_ringparam *ring)
 {
 	struct efx_nic *efx = netdev_priv(net_dev);
+	u32 txq_entries;
 
 	if (ring->rx_mini_pending || ring->rx_jumbo_pending ||
 	    ring->rx_pending > EFX_MAX_DMAQ_SIZE ||
 	    ring->tx_pending > EFX_MAX_DMAQ_SIZE)
 		return -EINVAL;
 
-	if (ring->rx_pending < EFX_MIN_RING_SIZE ||
-	    ring->tx_pending < EFX_MIN_RING_SIZE) {
+	if (ring->rx_pending < EFX_RXQ_MIN_ENT) {
 		netif_err(efx, drv, efx->net_dev,
-			  "TX and RX queues cannot be smaller than %ld\n",
-			  EFX_MIN_RING_SIZE);
+			  "RX queues cannot be smaller than %u\n",
+			  EFX_RXQ_MIN_ENT);
 		return -EINVAL;
 	}
 
-	return efx_realloc_channels(efx, ring->rx_pending, ring->tx_pending);
+	txq_entries = max(ring->tx_pending, EFX_TXQ_MIN_ENT(efx));
+	if (txq_entries != ring->tx_pending)
+		netif_warn(efx, drv, efx->net_dev,
+			   "increasing TX queue size to minimum of %u\n",
+			   txq_entries);
+
+	return efx_realloc_channels(efx, ring->rx_pending, txq_entries);
 }
 
 static int efx_ethtool_set_pauseparam(struct net_device *net_dev,