1 /*
2 * Copyright (c) 1990, 1991, 1993, 1994, 1995, 1996, 1997
3 * The Regents of the University of California. All rights reserved.
4 *
5 * Redistribution and use in source and binary forms, with or without
6 * modification, are permitted provided that: (1) source code distributions
7 * retain the above copyright notice and this paragraph in its entirety, (2)
8 * distributions including binary code include the above copyright notice and
9 * this paragraph in its entirety in the documentation or other materials
10 * provided with the distribution, and (3) all advertising materials mentioning
11 * features or use of this software display the following acknowledgement:
12 * ``This product includes software developed by the University of California,
13 * Lawrence Berkeley Laboratory and its contributors.'' Neither the name of
14 * the University nor the names of its contributors may be used to endorse
15 * or promote products derived from this software without specific prior
16 * written permission.
17 * THIS SOFTWARE IS PROVIDED ``AS IS'' AND WITHOUT ANY EXPRESS OR IMPLIED
18 * WARRANTIES, INCLUDING, WITHOUT LIMITATION, THE IMPLIED WARRANTIES OF
19 * MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE.
20 */
21
22 #include <sys/cdefs.h>
23 #ifndef lint
24 __RCSID("$NetBSD: print-vjc.c,v 1.6 2017/02/05 04:05:05 spz Exp $");
25 #endif
26
27 /* \summary: PPP Van Jacobson compression printer */
28
29 /* specification: RFC 1144 */
30
31 #ifdef HAVE_CONFIG_H
32 #include "config.h"
33 #endif
34
35 #include <netdissect-stdinc.h>
36
37 #include "netdissect.h"
38 #include "slcompress.h"
39 #include "ppp.h"
40
41 /*
42 * XXX - for BSD/OS PPP, what packets get supplied with a PPP header type
43 * of PPP_VJC and what packets get supplied with a PPP header type of
44 * PPP_VJNC? PPP_VJNC is for "UNCOMPRESSED_TCP" packets, and PPP_VJC
45 * is for COMPRESSED_TCP packets (PPP_IP is used for TYPE_IP packets).
46 *
47 * RFC 1144 implies that, on the wire, the packet type is *not* needed
48 * for PPP, as different PPP protocol types can be used; it only needs
49 * to be put on the wire for SLIP.
50 *
51 * It also indicates that, for compressed SLIP:
52 *
53 * If the COMPRESSED_TCP bit is set in the first byte, it's
54 * a COMPRESSED_TCP packet; that byte is the change byte, and
55 * the COMPRESSED_TCP bit, 0x80, isn't used in the change byte.
56 *
57 * If the upper 4 bits of the first byte are 7, it's an
58 * UNCOMPRESSED_TCP packet; that byte is the first byte of
59 * the UNCOMPRESSED_TCP modified IP header, with a connection
60 * number in the protocol field, and with the version field
61 * being 7, not 4.
62 *
63 * Otherwise, the packet is an IPv4 packet (where the upper 4 bits
64 * of the packet are 4).
65 *
66 * So this routine looks as if it's sort-of intended to handle
67 * compressed SLIP, although it doesn't handle UNCOMPRESSED_TCP
68 * correctly for that (it doesn't fix the version number and doesn't
69 * do anything to the protocol field), and doesn't check for COMPRESSED_TCP
70 * packets correctly for that (you only check the first bit - see
71 * B.1 in RFC 1144).
72 *
73 * But it's called for BSD/OS PPP, not SLIP - perhaps BSD/OS does weird
74 * things with the headers?
75 *
76 * Without a BSD/OS VJC-compressed PPP trace, or knowledge of what the
77 * BSD/OS VJC code does, we can't say what's the case.
78 *
79 * We therefore leave "proto" - which is the PPP protocol type - in place,
80 * *not* marked as unused, for now, so that GCC warnings about the
81 * unused argument remind us that we should fix this some day.
82 *
83 * XXX - also, it fetches the TCP checksum field in COMPRESSED_TCP
84 * packets directly, rather than with EXTRACT_16BITS(); RFC 1144 says
85 * it's "the unmodified TCP checksum", which would imply that it's
86 * big-endian, but perhaps, on the platform where this was developed,
87 * the packets were munged by the networking stack before being handed
88 * to the packet capture mechanism.
89 */
90 int
vjc_print(netdissect_options * ndo,register const char * bp,u_short proto _U_)91 vjc_print(netdissect_options *ndo, register const char *bp, u_short proto _U_)
92 {
93 int i;
94
95 switch (bp[0] & 0xf0) {
96 case TYPE_IP:
97 if (ndo->ndo_eflag)
98 ND_PRINT((ndo, "(vjc type=IP) "));
99 return PPP_IP;
100 case TYPE_UNCOMPRESSED_TCP:
101 if (ndo->ndo_eflag)
102 ND_PRINT((ndo, "(vjc type=raw TCP) "));
103 return PPP_IP;
104 case TYPE_COMPRESSED_TCP:
105 if (ndo->ndo_eflag)
106 ND_PRINT((ndo, "(vjc type=compressed TCP) "));
107 for (i = 0; i < 8; i++) {
108 if (bp[1] & (0x80 >> i))
109 ND_PRINT((ndo, "%c", "?CI?SAWU"[i]));
110 }
111 if (bp[1])
112 ND_PRINT((ndo, " "));
113 ND_PRINT((ndo, "C=0x%02x ", bp[2]));
114 ND_PRINT((ndo, "sum=0x%04x ", *(const u_short *)&bp[3]));
115 return -1;
116 case TYPE_ERROR:
117 if (ndo->ndo_eflag)
118 ND_PRINT((ndo, "(vjc type=error) "));
119 return -1;
120 default:
121 if (ndo->ndo_eflag)
122 ND_PRINT((ndo, "(vjc type=0x%02x) ", bp[0] & 0xf0));
123 return -1;
124 }
125 }
126