tcpdump mailing list archives
Re: PROBLEM: Software injected vlan tagged packets are unable to be identified using recent BPF modifications
From: Bill Fenner <fenner () gmail com>
Date: Thu, 10 Jan 2013 15:37:46 -0500
On Mon, Jan 7, 2013 at 10:04 PM, Paul Pearce <pearce () cs berkeley edu> wrote:
However, raw vlan tagged packets that are *injected* into the interface using libpcap's pcap_inject() (which is just a fancy wrapper for the send() syscall) are not identified by filters using the recent BPF modifications. The bug manifests itself if you attempt to use the new BPF modifications to filter vlan tagged packets on a live interface. All packets from the medium show up, but all injected packets are dropped.
Given that the vlan tag metadata is supplied to userland with PACKET_AUXDATA, does the symmetrical sendmsg() with PACKET_AUXDATA work to put the vlan info in the metadata? I.e., this would require modifying pcap_inject() to parse the packet and extract the VLAN tag info into a struct tpacket_auxdata, but obviously you could write a little test program to test the underlying PF_PACKET socket behavior. Even if it doesn't currently work, I think this may be a more acceptable change ("provide a way to set PACKET_AUXDATA using sendmsg") than having the packet send code munge/parse the vlan tag on output. Bill _______________________________________________ tcpdump-workers mailing list tcpdump-workers () lists tcpdump org https://lists.sandelman.ca/mailman/listinfo/tcpdump-workers
Current thread:
- Re: PROBLEM: Software injected vlan tagged packets are unable to be identified using recent BPF modifications Ani Sinha (Jan 07)
- Re: PROBLEM: Software injected vlan tagged packets are unable to be identified using recent BPF modifications Paul Pearce (Jan 07)
- Re: PROBLEM: Software injected vlan tagged packets are unable to be identified using recent BPF modifications Bill Fenner (Jan 10)
- Re: PROBLEM: Software injected vlan tagged packets are unable to be identified using recent BPF modifications Paul Pearce (Jan 07)