DeforaNetworks/fwknop
DeforaNetworks/fwknop
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[server] Calculate payload length from IP header

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Github user Scotte noticed that in his setup a 'VSS-Monitoring ethernet trailer'
was being added to incoming Ethernet frames that contained SPA packets. This
caused base64 decoding to break because the packet data length was calculated
from what libpcap returned for the frame (so these bytes became included in the
SPA payload itself). This issue was reported as #163 on github.

This commit has fwknopd calculate the SPA payload length using the length field
in the IP header so that any trailing bytes in the Ethernet frame are not
included. This solution also applies to the Ethernet Frame Check Sequence issue
(#126).
This commit is contained in:
Michael Rash 2015-07-17 00:05:10 -07:00
parent 042bf2d438
commit e7b48af47c
2 changed files with 12 additions and 16 deletions
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24
server/process_packet.c
View File

@ -58,6 +58,7 @@ process_packet(unsigned char *args, const struct pcap_pkthdr *packet_header,
unsigned char *pkt_data;
unsigned short pkt_data_len;
unsigned char *pkt_end;
unsigned char *fr_end;
unsigned int ip_hdr_words;
@ -85,7 +86,7 @@ process_packet(unsigned char *args, const struct pcap_pkthdr *packet_header,
/* Determine packet end.
*/
pkt_end = (unsigned char *) packet + packet_header->caplen;
fr_end = (unsigned char *) packet + packet_header->caplen;
/* The ethernet header.
*/
@ -128,7 +129,7 @@ process_packet(unsigned char *args, const struct pcap_pkthdr *packet_header,
/* If IP header is past calculated packet end, bail.
*/
if ((unsigned char*)(iph_p + 1) > pkt_end)
if ((unsigned char*)(iph_p + 1) > fr_end)
return;
/* ip_hdr_words is the number of 32 bit words in the IP header. After
@ -140,19 +141,14 @@ 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.
/* Make sure to calculate the packet end based on the length in the
* IP header. This allows additional bytes that may be added to the
* frame (such as a 4-byte Ethernet Frame Check Sequence) to not
* interfere with SPA operations.
*/
if(((unsigned char*)iph_p)+ntohs(iph_p->tot_len) == pkt_end-FCS_HEADER_LEN) {
log_msg(LOG_DEBUG, "Adjusting packet end to account for FCS header on Ethernet frame");
pkt_end -= FCS_HEADER_LEN;
}
pkt_end = ((unsigned char*)iph_p)+ntohs(iph_p->tot_len);
if(pkt_end > fr_end)
return;
/* Now, find the packet data payload (depending on IPPROTO).
*/

4
server/process_packet.h
View File

@ -33,7 +33,6 @@
#define IPV4_VER_MASK 0x15
#define MIN_IPV4_WORDS 0x05
#define FCS_HEADER_LEN 0x04
/* For items not defined by this system
*/
@ -47,7 +46,8 @@
/* Prototypes
*/
#if USE_LIBPCAP
void process_packet(unsigned char *args, const struct pcap_pkthdr *packet_header, const unsigned char *packet);
void process_packet(unsigned char *args,
const struct pcap_pkthdr *packet_header, const unsigned char *packet);
#endif
#endif /* PROCESS_PACKET_H */