datapath: Don't drop MTU-sized VLAN packets from userspace

Before transimitting a packet, the datapath checks that the packet
length is not greater than the MTU.  It determines the length based on
the 'protocol' field in the skb.  If 'protocol' is ETH_P_8021Q, it reduces
the packet length as stored in the 'len' field by four bytes, which
is the size of a VLAN tag header.  Unfortunately, packets that arrived
from userspace were not having the 'protocol' field set, which would
cause MTU-sized packets to be dropped.  This commit sets the 'protocol'
field appropriately.

Thanks to Ben Pfaff for the help diagnosing this issue.

NIC-17 and NIC-26

diff --git a/datapath/datapath.c b/datapath/datapath.c
index 1460215..b0dbe7f 100644 (file)
--- a/datapath/datapath.c
+++ b/datapath/datapath.c
@@ -1127,6 +1127,7 @@ static int do_execute(struct datapath *dp, const struct odp_execute *executep)
        struct odp_flow_key key;
        struct sk_buff *skb;
        struct sw_flow_actions *actions;
+       struct ethhdr *eth;
        int err;
 
        err = -EFAULT;
@@ -1166,6 +1167,17 @@ static int do_execute(struct datapath *dp, const struct odp_execute *executep)
                           execute.length))
                goto error_free_skb;
 
+       skb_reset_mac_header(skb);
+       eth = eth_hdr(skb);
+
+    /* Normally, setting the skb 'protocol' field would be handled by a
+     * call to eth_type_trans(), but it assumes there's a sending
+     * device, which we may not have. */
+       if (ntohs(eth->h_proto) >= 1536)
+               skb->protocol = eth->h_proto;
+       else
+               skb->protocol = htons(ETH_P_802_2);
+
        flow_extract(skb, execute.in_port, &key);
        err = execute_actions(dp, skb, &key, actions->actions,
                              actions->n_actions, GFP_KERNEL);