net: reset mac header in dev_start_xmit()

On 64 bit arches :

There is a off-by-one error in qdisc_pkt_len_init() because
mac_header is not set in xmit path.

skb_mac_header() returns an out of bound value that was
harmless because hdr_len is an 'unsigned int'

On 32bit arches, the error is abysmal.

This patch is also a prereq for "macvlan: add multicast filter"

Signed-off-by: Eric Dumazet <edumazet@google.com>
Cc: Ben Greear <greearb@candelatech.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/net/core/dev.c b/net/core/dev.c
index 65da698..2f31bf9 100644 (file)
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -2835,6 +2835,8 @@ int dev_queue_xmit(struct sk_buff *skb)
        struct Qdisc *q;
        int rc = -ENOMEM;
 
+       skb_reset_mac_header(skb);
+
        /* Disable soft irqs for various locks below. Also
         * stops preemption for RCU.
         */