[PATCH 04/04]: pcap-linux: reconstruct VLAN headers from tpacket2_hdr

[Patrick McHardy <kaber () trash net>]

pcap-linux: reconstruct VLAN headers from tpacket2_hdr

From: Patrick McHardy <kaber () trash net>

Similar to PACKET_AUXDATA for non-mmaped sockets, the VLAN TCI is
present in a new member of struct tpacket2_hdr. Use it to reconstruct
the VLAN header when necessary.
---

 pcap-linux.c |   28 ++++++++++++++++++++++++++++
 1 files changed, 28 insertions(+), 0 deletions(-)


diff --git a/pcap-linux.c b/pcap-linux.c
index 50d4389..1ffa2e4 100644
--- a/pcap-linux.c
+++ b/pcap-linux.c
@@ -1965,6 +1965,17 @@ prepare_tpacket_socket(pcap_t *handle)
                return 0;
        }
        handle->md.tp_version = TPACKET_V2;
+
+       /* Reserve space for VLAN tag reconstruction */
+       val = VLAN_TAG_LEN;
+       if (setsockopt(handle->fd, SOL_PACKET, PACKET_RESERVE, &val,
+                      sizeof(val)) < 0) {
+               snprintf(handle->errbuf, PCAP_ERRBUF_SIZE,
+                        "can't set up reserve on socket %d: %d-%s",
+                        handle->fd, errno, pcap_strerror(errno));
+               return 0;
+       }
+
 #endif /* HAVE_TPACKET2 */
        return 1;
 }
@@ -2281,6 +2292,23 @@ pcap_read_linux_mmap(pcap_t *handle, int max_packets, pcap_handler callback,
                        pcaphdr.len += SLL_HDR_LEN;
                }
 
+#ifdef HAVE_TPACKET2
+               if (handle->md.tp_version == TPACKET_V2 && h.h2->tp_vlan_tci &&
+                   tp_snaplen >= 2 * ETH_ALEN) {
+                       struct vlan_tag *tag;
+
+                       bp -= VLAN_TAG_LEN;
+                       memmove(bp, bp + VLAN_TAG_LEN, 2 * ETH_ALEN);
+
+                       tag = (struct vlan_tag *)(bp + 2 * ETH_ALEN);
+                       tag->vlan_tpid = htons(ETH_P_8021Q);
+                       tag->vlan_tci = htons(h.h2->tp_vlan_tci);
+
+                       pcaphdr.caplen += VLAN_TAG_LEN;
+                       pcaphdr.len += VLAN_TAG_LEN;
+               }
+#endif
+
                /* pass the packet to the user */
                pkts++;
                callback(user, &pcaphdr, bp);

-
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