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1 /*
2  * Copyright (c) 2013 The TCPDUMP project
3  * All rights reserved.
4  *
5  * Redistribution and use in source and binary forms, with or without
6  * modification, are permitted provided that the following conditions
7  * are met:
8  * 1. Redistributions of source code must retain the above copyright
9  *    notice, this list of conditions and the following disclaimer.
10  * 2. Redistributions in binary form must reproduce the above copyright
11  *    notice, this list of conditions and the following disclaimer in the
12  *    documentation and/or other materials provided with the distribution.
13  *
14  * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
15  * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
16  * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
17  * FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
18  * COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
19  * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
20  * BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
21  * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
22  * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
23  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN
24  * ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
25  * POSSIBILITY OF SUCH DAMAGE.
26  */
27 
28 /* \summary: ZeroMQ Message Transport Protocol (ZMTP) printer */
29 
30 #ifdef HAVE_CONFIG_H
31 #include <config.h>
32 #endif
33 
34 #include "netdissect-stdinc.h"
35 
36 #include "netdissect.h"
37 #include "extract.h"
38 
39 
40 /* Maximum number of ZMTP/1.0 frame body bytes (without the flags) to dump in
41  * hex and ASCII under a single "-v" flag.
42  */
43 #define VBYTES 128
44 
45 /*
46  * Below is an excerpt from the "13/ZMTP" specification:
47  *
48  * A ZMTP message consists of 1 or more frames.
49  *
50  * A ZMTP frame consists of a length, followed by a flags field and a frame
51  * body of (length - 1) octets. Note: the length includes the flags field, so
52  * an empty frame has a length of 1.
53  *
54  * For frames with a length of 1 to 254 octets, the length SHOULD BE encoded
55  * as a single octet. The minimum valid length of a frame is 1 octet, thus a
56  * length of 0 is invalid and such frames SHOULD be discarded silently.
57  *
58  * For frames with lengths of 255 and greater, the length SHALL BE encoded as
59  * a single octet with the value 255, followed by the length encoded as a
60  * 64-bit unsigned integer in network byte order. For frames with lengths of
61  * 1 to 254 octets this encoding MAY be also used.
62  *
63  * The flags field consists of a single octet containing various control
64  * flags. Bit 0 is the least significant bit.
65  *
66  * - Bit 0 (MORE): More frames to follow. A value of 0 indicates that there
67  *   are no more frames to follow. A value of 1 indicates that more frames
68  *   will follow. On messages consisting of a single frame the MORE flag MUST
69  *   be 0.
70  *
71  * - Bits 1-7: Reserved. Bits 1-7 are reserved for future use and SHOULD be
72  *   zero.
73  */
74 
75 static const u_char *
zmtp1_print_frame(netdissect_options * ndo,const u_char * cp,const u_char * ep)76 zmtp1_print_frame(netdissect_options *ndo, const u_char *cp, const u_char *ep)
77 {
78 	uint64_t body_len_declared, body_len_captured, header_len;
79 	uint8_t flags;
80 
81 	ND_PRINT("\n\t");
82 
83 	if (GET_U_1(cp) != 0xFF) {	/* length/0xFF */
84 		header_len = 1; /* length */
85 		body_len_declared = GET_U_1(cp);
86 		ND_PRINT(" frame flags+body  (8-bit) length %" PRIu64, body_len_declared);
87 	} else {
88 		header_len = 1 + 8; /* 0xFF, length */
89 		ND_PRINT(" frame flags+body (64-bit) length");
90 		ND_TCHECK_LEN(cp, header_len); /* 0xFF, length */
91 		body_len_declared = GET_BE_U_8(cp + 1);
92 		ND_PRINT(" %" PRIu64, body_len_declared);
93 	}
94 	if (body_len_declared == 0)
95 		return cp + header_len; /* skip to the next frame */
96 	ND_TCHECK_LEN(cp, header_len + 1); /* ..., flags */
97 	flags = GET_U_1(cp + header_len);
98 
99 	body_len_captured = ep - cp - header_len;
100 	if (body_len_declared > body_len_captured)
101 		ND_PRINT(" (%" PRIu64 " captured)", body_len_captured);
102 	ND_PRINT(", flags 0x%02x", flags);
103 
104 	if (ndo->ndo_vflag) {
105 		uint64_t body_len_printed = ND_MIN(body_len_captured, body_len_declared);
106 
107 		ND_PRINT(" (%s|%s|%s|%s|%s|%s|%s|%s)",
108 			flags & 0x80 ? "MBZ" : "-",
109 			flags & 0x40 ? "MBZ" : "-",
110 			flags & 0x20 ? "MBZ" : "-",
111 			flags & 0x10 ? "MBZ" : "-",
112 			flags & 0x08 ? "MBZ" : "-",
113 			flags & 0x04 ? "MBZ" : "-",
114 			flags & 0x02 ? "MBZ" : "-",
115 			flags & 0x01 ? "MORE" : "-");
116 
117 		if (ndo->ndo_vflag == 1)
118 			body_len_printed = ND_MIN(VBYTES + 1, body_len_printed);
119 		if (body_len_printed > 1) {
120 			ND_PRINT(", first %" PRIu64 " byte(s) of body:", body_len_printed - 1);
121 			hex_and_ascii_print(ndo, "\n\t ", cp + header_len + 1, body_len_printed - 1);
122 		}
123 	}
124 
125 	/*
126 	 * Do not advance cp by the sum of header_len and body_len_declared
127 	 * before each offset has successfully passed ND_TCHECK_LEN() as the
128 	 * sum can roll over (9 + 0xfffffffffffffff7 = 0) and cause an
129 	 * infinite loop.
130 	 */
131 	cp += header_len;
132 	ND_TCHECK_LEN(cp, body_len_declared); /* Next frame within the buffer ? */
133 	return cp + body_len_declared;
134 
135 trunc:
136 	nd_trunc_longjmp(ndo);
137 }
138 
139 void
zmtp1_print(netdissect_options * ndo,const u_char * cp,u_int len)140 zmtp1_print(netdissect_options *ndo, const u_char *cp, u_int len)
141 {
142 	const u_char *ep = ND_MIN(ndo->ndo_snapend, cp + len);
143 
144 	ndo->ndo_protocol = "zmtp1";
145 	ND_PRINT(": ZMTP/1.0");
146 	while (cp < ep)
147 		cp = zmtp1_print_frame(ndo, cp, ep);
148 }
149 
150 /* The functions below decode a ZeroMQ datagram, supposedly stored in the "Data"
151  * field of an ODATA/RDATA [E]PGM packet. An excerpt from zmq_pgm(7) man page
152  * follows.
153  *
154  * In order for late joining consumers to be able to identify message
155  * boundaries, each PGM datagram payload starts with a 16-bit unsigned integer
156  * in network byte order specifying either the offset of the first message frame
157  * in the datagram or containing the value 0xFFFF if the datagram contains
158  * solely an intermediate part of a larger message.
159  *
160  * Note that offset specifies where the first message begins rather than the
161  * first message part. Thus, if there are trailing message parts at the
162  * beginning of the packet the offset ignores them and points to first initial
163  * message part in the packet.
164  */
165 
166 static const u_char *
zmtp1_print_intermediate_part(netdissect_options * ndo,const u_char * cp,const u_int len)167 zmtp1_print_intermediate_part(netdissect_options *ndo, const u_char *cp, const u_int len)
168 {
169 	u_int frame_offset;
170 	u_int remaining_len;
171 
172 	frame_offset = GET_BE_U_2(cp);
173 	ND_PRINT("\n\t frame offset 0x%04x", frame_offset);
174 	cp += 2;
175 	remaining_len = ND_BYTES_AVAILABLE_AFTER(cp); /* without the frame length */
176 
177 	if (frame_offset == 0xFFFF)
178 		frame_offset = len - 2; /* always within the declared length */
179 	else if (2 + frame_offset > len) {
180 		ND_PRINT(" (exceeds datagram declared length)");
181 		goto trunc;
182 	}
183 
184 	/* offset within declared length of the datagram */
185 	if (frame_offset) {
186 		ND_PRINT("\n\t frame intermediate part, %u bytes", frame_offset);
187 		if (frame_offset > remaining_len)
188 			ND_PRINT(" (%u captured)", remaining_len);
189 		if (ndo->ndo_vflag) {
190 			u_int len_printed = ND_MIN(frame_offset, remaining_len);
191 
192 			if (ndo->ndo_vflag == 1)
193 				len_printed = ND_MIN(VBYTES, len_printed);
194 			if (len_printed > 1) {
195 				ND_PRINT(", first %u byte(s):", len_printed);
196 				hex_and_ascii_print(ndo, "\n\t ", cp, len_printed);
197 			}
198 		}
199 	}
200 	return cp + frame_offset;
201 
202 trunc:
203 	nd_trunc_longjmp(ndo);
204 }
205 
206 void
zmtp1_datagram_print(netdissect_options * ndo,const u_char * cp,const u_int len)207 zmtp1_datagram_print(netdissect_options *ndo, const u_char *cp, const u_int len)
208 {
209 	const u_char *ep = ND_MIN(ndo->ndo_snapend, cp + len);
210 
211 	ndo->ndo_protocol = "zmtp1";
212 	cp = zmtp1_print_intermediate_part(ndo, cp, len);
213 	while (cp < ep)
214 		cp = zmtp1_print_frame(ndo, cp, ep);
215 }
216