On Tue, 2003-10-07 at 11:06, Christian Darnell wrote:
> Hi Ben and all others,
>
> Just to clarify for other who hasn't been a part of this discussion before.
>
> ---- 8< ----
> When trying to grab a packet with pcap when using VLAN the beginning of the
> packet is corrupt an the VLAN TCI bits are missing. This is only a problem
> when sniffing on incoming traffic not outgoing.
>
> 00 60 08 50 00 60 08 50 26 2a 00 60 08 6a b4 53 xx xx xx xx 08 00 45 00
> ^^^^^^^^^^^ ^^^^^^^^^^^^
> Where does these bytes come from? Bytes missing (VLAN header)?
>
> The correct MAC addresses here are:
> 00 60 08 50 26 2a and 00 60 08 6a b4 53
> ---- 8< ----
This is because the VLAN code is mangling shared data.
You need to do something like this:
--- linux-2.4/net/8021q/vlan_dev.c.org 2003-02-25 15:23:09.000000000
+0100
+++ linux-2.4/net/8021q/vlan_dev.c 2003-10-07 16:01:29.000000000 +0200
@@ -75,7 +75,12 @@
static inline struct sk_buff *vlan_check_reorder_header(struct sk_buff
*skb)
{
if (VLAN_DEV_INFO(skb->dev)->flags & 1) {
- skb = skb_share_check(skb, GFP_ATOMIC);
+ if (skb_shared(skb) || skb_cloned(skb)) {
+ struct sk_buff *nskb;
+ nskb = skb_copy(skb, GFP_ATOMIC);
+ kfree_skb(skb);
+ skb = nskb;
+ }
if (skb) {
/* Lifted from Gleb's VLAN code... */
memmove(skb->data - ETH_HLEN,
Christian, could you try this out?
Regarding sharing, the following should be applied as well.
The VLAN code is handed shared sk_buff's, but doesn't handle them
as such.
--- linux-2.4/net/8021q/vlan.c.org 2003-02-25 15:23:09.000000000 +0100
+++ linux-2.4/net/8021q/vlan.c 2003-10-07 16:02:52.000000000 +0200
@@ -67,7 +67,7 @@
type: __constant_htons(ETH_P_8021Q),
dev: NULL,
func: vlan_skb_recv, /* VLAN receive method */
- data: (void *)(-1), /* Set here '(void *)1' when this code can SHARE
SKBs */
+ data: NULL, /* Set here '(void *)1' when this code can SHARE
SKBs */
next: NULL
};
I guess this is a special case of "off-by-one" ;-)
-Tommy
