net: more accurate network taps in transmit path

dev_queue_xmit_nit() should be called right before ndo_start_xmit()
calls or we might give wrong packet contents to taps users :

Packet checksum can be changed, or packet can be linearized or
segmented, and segments partially sent for the later case.

Also a memory allocation can fail and packet never really hit the
driver entry point.

Reported-by: Jamie Gloudon <jamie.gloudon@gmail.com>
Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 6 insertions, 3 deletions

diff --git a/net/core/dev.c b/net/core/dev.c
index dcc673d0674c..52cd1d7f004a 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -2213,9 +2213,6 @@ int dev_hard_start_xmit(struct sk_buff *skb, struct net_device *dev,
                 if (dev->priv_flags & IFF_XMIT_DST_RELEASE)
                         skb_dst_drop(skb);
 
-                if (!list_empty(&ptype_all))
-                        dev_queue_xmit_nit(skb, dev);
-
                 features = netif_skb_features(skb);
 
                 if (vlan_tx_tag_present(skb) &&
@@ -2250,6 +2247,9 @@ int dev_hard_start_xmit(struct sk_buff *skb, struct net_device *dev,
                         }
                 }
 
+                if (!list_empty(&ptype_all))
+                        dev_queue_xmit_nit(skb, dev);
+
                 skb_len = skb->len;
                 rc = ops->ndo_start_xmit(skb, dev);
                 trace_net_dev_xmit(skb, rc, dev, skb_len);
@@ -2272,6 +2272,9 @@ gso:
                 if (dev->priv_flags & IFF_XMIT_DST_RELEASE)
                         skb_dst_drop(nskb);
 
+                if (!list_empty(&ptype_all))
+                        dev_queue_xmit_nit(nskb, dev);
+
                 skb_len = nskb->len;
                 rc = ops->ndo_start_xmit(nskb, dev);
                 trace_net_dev_xmit(nskb, rc, dev, skb_len);