RE: [Bridge] RE: Re: [PATCH/RFC] Let {ip, arp}tables "see" bridged VLAN tagged{I,AR}P packets

-----Original Message-----
From: Christian Darnell [mailto:Christian.Darnell@se.flextronics.com]
Sent: Wednesday, October 08, 2003 10:18 AM
To: 'Tommy Christensen'
Cc: netdev@oss.sgi.com; 'Linux 802.1Q VLAN'; bridge
Subject: RE: [Bridge] RE: [VLAN] Re: [PATCH/RFC] Let {ip, arp}tables
"see" bridged VLAN tagged{I,AR}P packets



-----Original Message-----

quoted

From: Tommy Christensen [mailto:tommy.christensen@tpack.net]
Sent: Wednesday, October 08, 2003 10:09 AM
To: Christian Darnell
Cc: 'Linux 802.1Q VLAN'; Bart De Schuymer; netdev@oss.sgi.com; bridge
Subject: Re: [Bridge] RE: [VLAN] Re: [PATCH/RFC] Let {ip, arp}tables
"see" bridged VLAN tagged{I,AR}P packets



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

quoted

+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?

Thanks Tommy! I tried this (on kernel 2.4.22) and it works great!

Hi again, when the problem with VLAN and pcap was solved I found a bug in
pcap. The problem is that pcap_setfilter doesn't work correctly when using
vlan x. The problem is that pcap don't mask VID. This results in that for
packets with priority (802.1q) set to 0 the vlan x filter works fine, but
when the packet has a priority != 0 the vlan x fails. 

An example:
If one have a vlan with VID = 2 and sniffing using the filter "vlan 2"
packets with priority = 0 will be shown. Changing to priority = 1 the
packets wont appear, if one changes the filter to "vlan 8194" the packets
will appear.

Fixing so pcap will mask the TCI field with "& 0xfff " to get the VID should
probably fix this problem. I have try to locate where this check is
performed in the pcap code but with no success. I think
gencode.c::gen_vlan(vlan_num) has something to do with...

Is there someone who knows the pcap code and know where this check is done?
I have tried with tcpdump-workers@tcpdump.org before without any response,
is there anyone who knows how to contact the maintainers of the libpcap?


Best regards,

Christian Darnell

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