Re: vlan tagged packets and libpcap breakage

[Ani Sinha <ani () aristanetworks com>]

On Thu, 6 Dec 2012, Michael Richardson wrote:

> Date: Thu, 6 Dec 2012 17:59:13
> From: Michael Richardson <mcr () sandelman ca>
> To: Eric W. Biederman <ebiederm () xmission com>
> Cc: ani () aristanetworks com, tcpdump-workers () lists tcpdump org,
>     netdev () vger kernel org, Francesco Ruggeri <fruggeri () aristanetworks com>
> Subject: Re: [tcpdump-workers] vlan tagged packets and libpcap breakage
>
>
> > > > > > "Eric" == Eric W Biederman <ebiederm () xmission com> writes:
>     Eric> It is a bit odd that you are indenting with spaces instead of tabs
>     Eric> in a file that is indented with tab.  Again libpcap isn't my code so I
>     Eric> don't care but someone else might.

Here's an updated patch. I have converted spaces to tabs consistent with
rest of the file. I have also set up github and sent a pull request

 :

commit b977ebd9d9608bb8a8e4927e7a6286bdfd6b94a8
Author: Ani Sinha <ani () aristanetworks com>
Date:   Mon Dec 10 14:58:15 2012 -0800

    Linux kernel 3.0 uses TP_STATUS_VLAN_VALID flag in packet
    auxilliary data aux->tp_status to indicate a packet tagged
    with a valid vlan ID 0 with another packet that is not
    vlan tagged. Use this flag to check for the presence of
    a vlan tagged packet. Also be careful not to cause any
    breakage when libpcap is compiled against a newer kernel
    (>=3.0) and used on top of an older kernel that does not
    use this flag.

    Signed-off-by: Ani Sinha <ani () aristanetworks com>

diff --git a/pcap-linux.c b/pcap-linux.c
index a42c3ac..ffcabdf 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 +3943,12 @@ 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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