Commit 104ba78c authored Oct 26, 2016 by Willem de Bruijn Committed by David S. Miller Oct 29, 2016

packet: on direct_xmit, limit tso and csum to supported devices



When transmitting on a packet socket with PACKET_VNET_HDR and
PACKET_QDISC_BYPASS, validate device support for features requested
in vnet_hdr.

Drop TSO packets sent to devices that do not support TSO or have the
feature disabled. Note that the latter currently do process those
packets correctly, regardless of not advertising the feature.

Because of SKB_GSO_DODGY, it is not sufficient to test device features
with netif_needs_gso. Full validate_xmit_skb is needed.

Switch to software checksum for non-TSO packets that request checksum
offload if that device feature is unsupported or disabled. Note that
similar to the TSO case, device drivers may perform checksum offload
correctly even when not advertising it.

When switching to software checksum, packets hit skb_checksum_help,
which has two BUG_ON checksum not in linear segment. Packet sockets
always allocate at least up to csum_start + csum_off + 2 as linear.

Tested by running github.com/wdebruij/kerneltools/psock_txring_vnet.c

  ethtool -K eth0 tso off tx on
  psock_txring_vnet -d $dst -s $src -i eth0 -l 2000 -n 1 -q -v
  psock_txring_vnet -d $dst -s $src -i eth0 -l 2000 -n 1 -q -v -N

  ethtool -K eth0 tx off
  psock_txring_vnet -d $dst -s $src -i eth0 -l 1000 -n 1 -q -v -G
  psock_txring_vnet -d $dst -s $src -i eth0 -l 1000 -n 1 -q -v -G -N

v2:
  - add EXPORT_SYMBOL_GPL(validate_xmit_skb_list)

Fixes: d346a3fa ("packet: introduce PACKET_QDISC_BYPASS socket option")
Signed-off-by: Willem de Bruijn <willemb@google.com>
Acked-by: Eric Dumazet <edumazet@google.com>
Acked-by: Daniel Borkmann <daniel@iogearbox.net>
Signed-off-by: David S. Miller <davem@davemloft.net>

parent 4700e9ce

net/core/dev.c

+1 −0

Original line number	Diff line number	Diff line
		@@ -3035,6 +3035,7 @@ struct sk_buff validate_xmit_skb_list(struct sk_buff skb, struct net_device *d
		}
		return head;
		}
		EXPORT_SYMBOL_GPL(validate_xmit_skb_list);

		static void qdisc_pkt_len_init(struct sk_buff *skb)
		{

net/packet/af_packet.c

+4 −5

Original line number	Diff line number	Diff line
		@@ -250,7 +250,7 @@ static void __fanout_link(struct sock sk, struct packet_sock po);
		static int packet_direct_xmit(struct sk_buff *skb)
		{
		struct net_device *dev = skb->dev;
		netdev_features_t features;
		struct sk_buff *orig_skb = skb;
		struct netdev_queue *txq;
		int ret = NETDEV_TX_BUSY;

		@@ -258,9 +258,8 @@ static int packet_direct_xmit(struct sk_buff *skb)
		!netif_carrier_ok(dev)))
		goto drop;

		features = netif_skb_features(skb);
		if (skb_needs_linearize(skb, features) &&
		__skb_linearize(skb))
		skb = validate_xmit_skb_list(skb, dev);
		if (skb != orig_skb)
		goto drop;

		txq = skb_get_tx_queue(dev, skb);
		@@ -280,7 +279,7 @@ static int packet_direct_xmit(struct sk_buff *skb)
		return ret;
		drop:
		atomic_long_inc(&dev->tx_dropped);
		kfree_skb(skb);
		kfree_skb_list(skb);
		return NET_XMIT_DROP;
		}

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