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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 static const char tstr[] = " [|zmtp1]";
40 
41 /* Maximum number of ZMTP/1.0 frame body bytes (without the flags) to dump in
42  * hex and ASCII under a single "-v" flag.
43  */
44 #define VBYTES 128
45 
46 /*
47  * Below is an excerpt from the "13/ZMTP" specification:
48  *
49  * A ZMTP message consists of 1 or more frames.
50  *
51  * A ZMTP frame consists of a length, followed by a flags field and a frame
52  * body of (length - 1) octets. Note: the length includes the flags field, so
53  * an empty frame has a length of 1.
54  *
55  * For frames with a length of 1 to 254 octets, the length SHOULD BE encoded
56  * as a single octet. The minimum valid length of a frame is 1 octet, thus a
57  * length of 0 is invalid and such frames SHOULD be discarded silently.
58  *
59  * For frames with lengths of 255 and greater, the length SHALL BE encoded as
60  * a single octet with the value 255, followed by the length encoded as a
61  * 64-bit unsigned integer in network byte order. For frames with lengths of
62  * 1 to 254 octets this encoding MAY be also used.
63  *
64  * The flags field consists of a single octet containing various control
65  * flags. Bit 0 is the least significant bit.
66  *
67  * - Bit 0 (MORE): More frames to follow. A value of 0 indicates that there
68  *   are no more frames to follow. A value of 1 indicates that more frames
69  *   will follow. On messages consisting of a single frame the MORE flag MUST
70  *   be 0.
71  *
72  * - Bits 1-7: Reserved. Bits 1-7 are reserved for future use and SHOULD be
73  *   zero.
74  */
75 
76 static const u_char *
zmtp1_print_frame(netdissect_options * ndo,const u_char * cp,const u_char * ep)77 zmtp1_print_frame(netdissect_options *ndo, const u_char *cp, const u_char *ep)
78 {
79 	uint64_t body_len_declared, body_len_captured, header_len;
80 	uint8_t flags;
81 
82 	ND_PRINT((ndo, "\n\t"));
83 	ND_TCHECK2(*cp, 1); /* length/0xFF */
84 
85 	if (cp[0] != 0xFF) {
86 		header_len = 1; /* length */
87 		body_len_declared = cp[0];
88 		ND_PRINT((ndo, " frame flags+body  (8-bit) length %" PRIu64, body_len_declared));
89 	} else {
90 		header_len = 1 + 8; /* 0xFF, length */
91 		ND_PRINT((ndo, " frame flags+body (64-bit) length"));
92 		ND_TCHECK2(*cp, header_len); /* 0xFF, length */
93 		body_len_declared = EXTRACT_64BITS(cp + 1);
94 		ND_PRINT((ndo, " %" PRIu64, body_len_declared));
95 	}
96 	if (body_len_declared == 0)
97 		return cp + header_len; /* skip to the next frame */
98 	ND_TCHECK2(*cp, header_len + 1); /* ..., flags */
99 	flags = cp[header_len];
100 
101 	body_len_captured = ep - cp - header_len;
102 	if (body_len_declared > body_len_captured)
103 		ND_PRINT((ndo, " (%" PRIu64 " captured)", body_len_captured));
104 	ND_PRINT((ndo, ", flags 0x%02x", flags));
105 
106 	if (ndo->ndo_vflag) {
107 		uint64_t body_len_printed = min(body_len_captured, body_len_declared);
108 
109 		ND_PRINT((ndo, " (%s|%s|%s|%s|%s|%s|%s|%s)",
110 			flags & 0x80 ? "MBZ" : "-",
111 			flags & 0x40 ? "MBZ" : "-",
112 			flags & 0x20 ? "MBZ" : "-",
113 			flags & 0x10 ? "MBZ" : "-",
114 			flags & 0x08 ? "MBZ" : "-",
115 			flags & 0x04 ? "MBZ" : "-",
116 			flags & 0x02 ? "MBZ" : "-",
117 			flags & 0x01 ? "MORE" : "-"));
118 
119 		if (ndo->ndo_vflag == 1)
120 			body_len_printed = min(VBYTES + 1, body_len_printed);
121 		if (body_len_printed > 1) {
122 			ND_PRINT((ndo, ", first %" PRIu64 " byte(s) of body:", body_len_printed - 1));
123 			hex_and_ascii_print(ndo, "\n\t ", cp + header_len + 1, body_len_printed - 1);
124 			ND_PRINT((ndo, "\n"));
125 		}
126 	}
127 
128 	/*
129 	 * Do not advance cp by the sum of header_len and body_len_declared
130 	 * before each offset has successfully passed ND_TCHECK2() as the
131 	 * sum can roll over (9 + 0xfffffffffffffff7 = 0) and cause an
132 	 * infinite loop.
133 	 */
134 	cp += header_len;
135 	ND_TCHECK2(*cp, body_len_declared); /* Next frame within the buffer ? */
136 	return cp + body_len_declared;
137 
138 trunc:
139 	ND_PRINT((ndo, "%s", tstr));
140 	return ep;
141 }
142 
143 void
zmtp1_print(netdissect_options * ndo,const u_char * cp,u_int len)144 zmtp1_print(netdissect_options *ndo, const u_char *cp, u_int len)
145 {
146 	const u_char *ep = min(ndo->ndo_snapend, cp + len);
147 
148 	ND_PRINT((ndo, ": ZMTP/1.0"));
149 	while (cp < ep)
150 		cp = zmtp1_print_frame(ndo, cp, ep);
151 }
152 
153 /* The functions below decode a ZeroMQ datagram, supposedly stored in the "Data"
154  * field of an ODATA/RDATA [E]PGM packet. An excerpt from zmq_pgm(7) man page
155  * follows.
156  *
157  * In order for late joining consumers to be able to identify message
158  * boundaries, each PGM datagram payload starts with a 16-bit unsigned integer
159  * in network byte order specifying either the offset of the first message frame
160  * in the datagram or containing the value 0xFFFF if the datagram contains
161  * solely an intermediate part of a larger message.
162  *
163  * Note that offset specifies where the first message begins rather than the
164  * first message part. Thus, if there are trailing message parts at the
165  * beginning of the packet the offset ignores them and points to first initial
166  * message part in the packet.
167  */
168 
169 static const u_char *
zmtp1_print_intermediate_part(netdissect_options * ndo,const u_char * cp,const u_int len)170 zmtp1_print_intermediate_part(netdissect_options *ndo, const u_char *cp, const u_int len)
171 {
172 	u_int frame_offset;
173 	uint64_t remaining_len;
174 
175 	ND_TCHECK2(*cp, 2);
176 	frame_offset = EXTRACT_16BITS(cp);
177 	ND_PRINT((ndo, "\n\t frame offset 0x%04x", frame_offset));
178 	cp += 2;
179 	remaining_len = ndo->ndo_snapend - cp; /* without the frame length */
180 
181 	if (frame_offset == 0xFFFF)
182 		frame_offset = len - 2; /* always within the declared length */
183 	else if (2 + frame_offset > len) {
184 		ND_PRINT((ndo, " (exceeds datagram declared length)"));
185 		goto trunc;
186 	}
187 
188 	/* offset within declared length of the datagram */
189 	if (frame_offset) {
190 		ND_PRINT((ndo, "\n\t frame intermediate part, %u bytes", frame_offset));
191 		if (frame_offset > remaining_len)
192 			ND_PRINT((ndo, " (%"PRIu64" captured)", remaining_len));
193 		if (ndo->ndo_vflag) {
194 			uint64_t len_printed = min(frame_offset, remaining_len);
195 
196 			if (ndo->ndo_vflag == 1)
197 				len_printed = min(VBYTES, len_printed);
198 			if (len_printed > 1) {
199 				ND_PRINT((ndo, ", first %"PRIu64" byte(s):", len_printed));
200 				hex_and_ascii_print(ndo, "\n\t ", cp, len_printed);
201 				ND_PRINT((ndo, "\n"));
202 			}
203 		}
204 	}
205 	return cp + frame_offset;
206 
207 trunc:
208 	ND_PRINT((ndo, "%s", tstr));
209 	return cp + len;
210 }
211 
212 void
zmtp1_print_datagram(netdissect_options * ndo,const u_char * cp,const u_int len)213 zmtp1_print_datagram(netdissect_options *ndo, const u_char *cp, const u_int len)
214 {
215 	const u_char *ep = min(ndo->ndo_snapend, cp + len);
216 
217 	cp = zmtp1_print_intermediate_part(ndo, cp, len);
218 	while (cp < ep)
219 		cp = zmtp1_print_frame(ndo, cp, ep);
220 }
221