diff --git a/server/process_packet.c b/server/process_packet.c index 79098241..72fca720 100644 --- a/server/process_packet.c +++ b/server/process_packet.c @@ -38,6 +38,7 @@ #include "process_packet.h" #include "incoming_spa.h" #include "utils.h" +#include "log_msg.h" void process_packet(unsigned char *args, const struct pcap_pkthdr *packet_header, @@ -134,6 +135,28 @@ process_packet(unsigned char *args, const struct pcap_pkthdr *packet_header, if (ip_hdr_words < MIN_IPV4_WORDS) return; + + /* Support for the cases where libpcap returns the Ethernet Frame Check + * Sequence (4 bytes at the end of the Ethernet frame) as part of the + * capture. libpcap returning the FCS is fairly rare. Default settings on + * the following system included an Ethernet FCS in the libpcap capture: + * BeagleBone Black rev C running 3.8.13-bone50 #1 SMP Tue May 13 + * 13:24:52 UTC 2014 armv7l GNU/Linux + * + * Calculate the new pkt_end from the length in the ip header. + */ + unsigned char *pcap_with_fcs_workaround_pkt_end = + ((unsigned char*)iph_p) + ntohs(iph_p->tot_len); + + /* Only accept the new end if it is shorter than the original pkt_end + * provided by libpcap. + */ + if(pcap_with_fcs_workaround_pkt_end < pkt_end) { + log_msg(LOG_DEBUG, "Adjusting packet end from %u to %u (likely due to Ethernet FCS being included in the capture)", pkt_end, pcap_with_fcs_workaround_pkt_end); + pkt_end = pcap_with_fcs_workaround_pkt_end; + } + + /* Now, find the packet data payload (depending on IPPROTO). */ src_ip = iph_p->saddr;