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

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Date:	Thu, 6 Dec 2012 16:55:00 -0800
From:	Ani Sinha <ani@...stanetworks.com>
To:	"Eric W. Biederman" <ebiederm@...ssion.com>
Cc:	Michael Richardson <mcr@...delman.ca>,
	tcpdump-workers@...ts.tcpdump.org, netdev@...r.kernel.org,
	Francesco Ruggeri <fruggeri@...stanetworks.com>
Subject: Re: [tcpdump-workers] vlan tagged packets and libpcap breakage

On Thu, Dec 6, 2012 at 2:19 PM, Eric W. Biederman <ebiederm@...ssion.com> wrote:
> Ani Sinha <ani@...stanetworks.com> 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 :

 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))
+#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;
--
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