network: Allow af_packet to transmit +4 bytes for VLAN packets.

This allows user-space to send a '1500' MTU VLAN packet on a
1500 MTU ethernet frame.  The extra 4 bytes of a VLAN header is
not usually charged against the MTU when other parts of the
network stack is transmitting vlans...

Signed-off-by: Ben Greear <greearb@candelatech.com>
Reviewed-by: Eric Dumazet <eric.dumazet@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 29 insertions, 2 deletions

diff --git a/net/packet/af_packet.c b/net/packet/af_packet.c
index c60649ec1193..5efef5b5879e 100644
--- a/net/packet/af_packet.c
+++ b/net/packet/af_packet.c
@@ -465,7 +465,7 @@ retry:
          */
 
         err = -EMSGSIZE;
-        if (len > dev->mtu + dev->hard_header_len)
+        if (len > dev->mtu + dev->hard_header_len + VLAN_HLEN)
                 goto out_unlock;
 
         if (!skb) {
@@ -496,6 +496,19 @@ retry:
                 goto retry;
         }
 
+        if (len > (dev->mtu + dev->hard_header_len)) {
+                /* Earlier code assumed this would be a VLAN pkt,
+                 * double-check this now that we have the actual
+                 * packet in hand.
+                 */
+                struct ethhdr *ehdr;
+                skb_reset_mac_header(skb);
+                ehdr = eth_hdr(skb);
+                if (ehdr->h_proto != htons(ETH_P_8021Q)) {
+                        err = -EMSGSIZE;
+                        goto out_unlock;
+                }
+        }
 
         skb->protocol = proto;
         skb->dev = dev;
@@ -1199,7 +1212,7 @@ static int packet_snd(struct socket *sock,
         }
 
         err = -EMSGSIZE;
-        if (!gso_type && (len > dev->mtu+reserve))
+        if (!gso_type && (len > dev->mtu + reserve + VLAN_HLEN))
                 goto out_unlock;
 
         err = -ENOBUFS;
@@ -1224,6 +1237,20 @@ static int packet_snd(struct socket *sock,
         if (err < 0)
                 goto out_free;
 
+        if (!gso_type && (len > dev->mtu + reserve)) {
+                /* Earlier code assumed this would be a VLAN pkt,
+                 * double-check this now that we have the actual
+                 * packet in hand.
+                 */
+                struct ethhdr *ehdr;
+                skb_reset_mac_header(skb);
+                ehdr = eth_hdr(skb);
+                if (ehdr->h_proto != htons(ETH_P_8021Q)) {
+                        err = -EMSGSIZE;
+                        goto out_free;
+                }
+        }
+
         skb->protocol = proto;
         skb->dev = dev;
         skb->priority = sk->sk_priority;