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Subject[PATCH 3.18 045/145] [PATCH 097/760] packet: on direct_xmit, limit tso and csum to supported devices
3.18-stable review patch.  If anyone has any objections, please let me know.


From: Willem de Bruijn <>

[ Upstream commit 104ba78c98808ae837d1f63aae58c183db5505df ]

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

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

- add EXPORT_SYMBOL_GPL(validate_xmit_skb_list)

Fixes: d346a3fae3ff ("packet: introduce PACKET_QDISC_BYPASS socket option")
Signed-off-by: Willem de Bruijn <>
Acked-by: Eric Dumazet <>
Acked-by: Daniel Borkmann <>
Signed-off-by: David S. Miller <>
Signed-off-by: Greg Kroah-Hartman <>
Signed-off-by: Greg Kroah-Hartman <>
net/core/dev.c | 1 +
net/packet/af_packet.c | 9 ++++-----
2 files changed, 5 insertions(+), 5 deletions(-)

--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -2741,6 +2741,7 @@ struct sk_buff *validate_xmit_skb_list(s
return head;

static void qdisc_pkt_len_init(struct sk_buff *skb)
--- a/net/packet/af_packet.c
+++ b/net/packet/af_packet.c
@@ -240,7 +240,7 @@ static void __fanout_link(struct sock *s
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;

@@ -248,9 +248,8 @@ static int packet_direct_xmit(struct sk_
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);
@@ -270,7 +269,7 @@ static int packet_direct_xmit(struct sk_
return ret;
- kfree_skb(skb);
+ kfree_skb_list(skb);

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