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This is Gerrit Renker code which: 

* makes checksum computation dependent
         upon the header CsCov field (cf. RFC 4340, 5.1)
       * removes the case where checksums are zero
         (unlike UDP/packet-udp, from which the code stems,
          zero checksums are illegal in DCCP (as in TCP))
       * fixes a minor typo - missing bitshift of the
         CCVal field

svn path=/trunk/; revision=19885
This commit is contained in:
Anders Broman 2006-11-14 05:45:28 +00:00
parent 06d1297a6b
commit e53bccdfca
1 changed files with 30 additions and 12 deletions
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42
epan/dissectors/packet-dcp.c
View File

@ -30,10 +30,21 @@
*/
/* Note: PROTOABBREV name collision problem, 'dccp' is used by Distributed Checksum
Clearinghouse Protocol.
This dissector should be named packet-dccp.c IMHO.
*/
/* NOTES:
*
* PROTOABBREV name collision problem, 'dccp' is used by
* Distributed Checksum Clearinghouse Protocol.
* This dissector should be named packet-dccp.c IMHO.
*
* Nov 13, 2006: makes checksum computation dependent
* upon the header CsCov field (cf. RFC 4340, 5.1)
* (Gerrit Renker)
*
* Nov 13, 2006: removes the case where checksums are zero
* (unlike UDP/packet-udp, from which the code stems,
* zero checksums are illegal in DCCP (as in TCP))
* (Gerrit Renker)
*/
#ifdef HAVE_CONFIG_H
# include "config.h"
@ -541,6 +552,16 @@ static void dissect_options(tvbuff_t *tvb, packet_info *pinfo _U_, proto_tree *d
} /* end while() */
}
/* compute DCCP checksum coverage according to RFC 4340, section 9 */
static inline guint dccp_csum_coverage(const e_dcphdr *dcph, guint len)
{
guint cov;
if (dcph->cscov == 0)
return len;
cov = (dcph->data_offset + dcph->cscov - 1) * sizeof(guint32);
return (cov > len)? len : cov;
}
static void dissect_dcp(tvbuff_t *tvb, packet_info *pinfo, proto_tree *tree)
{
@ -595,7 +616,8 @@ static void dissect_dcp(tvbuff_t *tvb, packet_info *pinfo, proto_tree *tree)
/* DBG("dcph->data_offset: %d\n", dcph->data_offset); */
dcph->cscov=tvb_get_guint8(tvb, offset+5)&0x0F;
/* DBG("dcph->cscov: %d\n", dcph->cscov); */
dcph->ccval=tvb_get_guint8(tvb, offset+5)&0xF0;
dcph->ccval=tvb_get_guint8(tvb, offset+5) &0xF0;
dcph->ccval >>= 4;
/* DBG("dcph->ccval: %d\n", dcph->ccval); */
dcph->checksum=tvb_get_ntohs(tvb, offset+6);
/* DBG("dcph->checksum: %d\n", dcph->checksum); */
@ -662,15 +684,11 @@ static void dissect_dcp(tvbuff_t *tvb, packet_info *pinfo, proto_tree *tree)
proto_tree_add_uint(dcp_tree, hf_dcp_ccval, tvb, offset + 5, 1, dcph->ccval);
proto_tree_add_uint(dcp_tree, hf_dcp_cscov, tvb, offset + 5, 1, dcph->cscov);
/* checksum analisys taken from packet-udp */
/* checksum analysis taken from packet-udp (difference: mandatory checksums in DCCP) */
reported_len = tvb_reported_length(tvb);
len = tvb_length(tvb);
if (dcph->checksum == 0) {
/* No checksum supplied in the packet */
proto_tree_add_uint_format_value(dcp_tree, hf_dcp_checksum, tvb,
offset + 6, 2, dcph->checksum, "0x%04x (none)", dcph->checksum);
} else if (!pinfo->fragmented && len >= reported_len) {
if (!pinfo->fragmented && len >= reported_len) {
/* The packet isn't part of a fragmented datagram and isn't
truncated, so we can checksum it.
@ -703,7 +721,7 @@ static void dissect_dcp(tvbuff_t *tvb, packet_info *pinfo, proto_tree *tree)
break;
}
cksum_vec[3].ptr = tvb_get_ptr(tvb, offset, len);
cksum_vec[3].len = reported_len;
cksum_vec[3].len = dccp_csum_coverage(dcph, reported_len);
computed_cksum = in_cksum(&cksum_vec[0], 4);
if (computed_cksum == 0) {
proto_tree_add_uint_format_value(dcp_tree, hf_dcp_checksum, tvb,