Subject: Re: [tcpdump-workers] vlan tagged packets and libpcap breakage

From: [email-masked] (Eric W. Biederman)
Date: Thu, 06 Dec 2012 17:03:44 -0800

Ani Sinha <[email-masked]> writes:

> On Thu, Dec 6, 2012 at 2:19 PM, Eric W. Biederman <[email-masked]> wrote:
>> Ani Sinha <[email-masked]> writes:
>>>>
>>>
>>> May be this?
>>
>> Two things.
>>
>> - TP_STATUS_VLAN_VALID lives in the tp_status field not the tp_vlan_tci field.
>> - To work on older kernels with binaries compiled with newer headers you
>>   first want to test for tp_vlan_tci == 0 and then look at the status field for
>>   TP_STATUS_VALID.
>
>
> trying again :

The patch is whitespace damaged.  And one of your test is using ||
instead of &&

Eric

>  pcap-linux.c |   50 +++++++++++++++++++++++++++++++-------------------
>  1 files changed, 31 insertions(+), 19 deletions(-)
>
> diff --git a/pcap-linux.c b/pcap-linux.c
> index a42c3ac..8e355d3 100644
> --- a/pcap-linux.c
> +++ b/pcap-linux.c
> @@ -133,6 +133,7 @@ static const char rcsid[] _U_ =
>  #include <sys/utsname.h>
>  #include <sys/mman.h>
>  #include <linux/if.h>
> +#include <linux/if_packet.h>
>  #include <netinet/in.h>
>  #include <linux/if_ether.h>
>  #include <net/if_arp.h>
> @@ -1543,7 +1544,13 @@ pcap_read_packet(pcap_t *handle, pcap_handler
> callback, u_char *userdata)
>   continue;
>
>   aux = (struct tpacket_auxdata *)CMSG_DATA(cmsg);
> - if (aux->tp_vlan_tci == 0)
> +#if defined(TP_STATUS_VLAN_VALID)
> +                        if ((aux->tp_vlan_tci == 0) ||
> !(aux->tp_status & TP_STATUS_VLAN_VALID))

The test should be && not ||.

> +#else
> + if (aux->tp_vlan_tci == 0) /* this is ambigious but without the
> +
> TP_STATUS_VLAN_VALID flag, there is
> +                                                      nothing that we can do */
> +#endif
>   continue;
>
>   len = packet_len > iov.iov_len ? iov.iov_len : packet_len;
> @@ -3936,7 +3926,12 @@ pcap_read_linux_mmap(pcap_t *handle, int
> max_packets, pcap_handler callback,
>   }
>
>  #ifdef HAVE_TPACKET2
> - if (handle->md.tp_version == TPACKET_V2 && h.h2->tp_vlan_tci &&
> +                if ((handle->md.tp_version == TPACKET_V2) &&
> +#if defined(TP_STATUS_VLAN_VALID)
> +                    (h.h2->tp_vlan_tci || (h.h2->tp_status &
> TP_STATUS_VLAN_VALID)) &&
> +#else
> +                    h.h2->tp_vlan_tci &&
> +#endif
>      handle->md.vlan_offset != -1 &&
>      tp_snaplen >= (unsigned int) handle->md.vlan_offset) {
>   struct vlan_tag *tag;