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 #include <sys/cdefs.h>
29 #ifndef lint
30 __RCSID("$NetBSD: print-zeromq.c,v 1.5 2024/09/02 16:15:33 christos Exp $");
31 #endif
32 
33 /* \summary: ZeroMQ Message Transport Protocol (ZMTP) printer */
34 /* specification: https://rfc.zeromq.org/spec/13/ */
35 
36 #include <config.h>
37 
38 #include "netdissect-stdinc.h"
39 
40 #include "netdissect.h"
41 #include "extract.h"
42 
43 
44 /* Maximum number of ZMTP/1.0 frame body bytes (without the flags) to dump in
45  * hex and ASCII under a single "-v" flag.
46  */
47 #define VBYTES 128
48 
49 static const struct tok flags_bm[] = {
50           { 0x01, "MORE"  },
51           { 0x02, "R1" },
52           { 0x04, "R2" },
53           { 0x08, "R3" },
54           { 0x10, "R4" },
55           { 0x20, "R5" },
56           { 0x40, "R6" },
57           { 0x80, "R7" },
58           { 0, NULL }
59 };
60 
61 /*
62  * Below is an excerpt from the "13/ZMTP" specification:
63  *
64  * A ZMTP message consists of 1 or more frames.
65  *
66  * A ZMTP frame consists of a length, followed by a flags field and a frame
67  * body of (length - 1) octets. Note: the length includes the flags field, so
68  * an empty frame has a length of 1.
69  *
70  * For frames with a length of 1 to 254 octets, the length SHOULD BE encoded
71  * as a single octet. The minimum valid length of a frame is 1 octet, thus a
72  * length of 0 is invalid and such frames SHOULD be discarded silently.
73  *
74  * For frames with lengths of 255 and greater, the length SHALL BE encoded as
75  * a single octet with the value 255, followed by the length encoded as a
76  * 64-bit unsigned integer in network byte order. For frames with lengths of
77  * 1 to 254 octets this encoding MAY be also used.
78  *
79  * The flags field consists of a single octet containing various control
80  * flags. Bit 0 is the least significant bit.
81  *
82  * - Bit 0 (MORE): More frames to follow. A value of 0 indicates that there
83  *   are no more frames to follow. A value of 1 indicates that more frames
84  *   will follow. On messages consisting of a single frame the MORE flag MUST
85  *   be 0.
86  *
87  * - Bits 1-7: Reserved. Bits 1-7 are reserved for future use and SHOULD be
88  *   zero.
89  */
90 
91 static const u_char *
zmtp1_print_frame(netdissect_options * ndo,const u_char * cp,const u_char * ep)92 zmtp1_print_frame(netdissect_options *ndo, const u_char *cp, const u_char *ep)
93 {
94           uint64_t body_len_declared, body_len_captured, header_len;
95           uint8_t flags;
96 
97           ND_PRINT("\n\t");
98 
99           if (GET_U_1(cp) != 0xFF) {    /* length/0xFF */
100                     header_len = 1; /* length */
101                     body_len_declared = GET_U_1(cp);
102                     ND_PRINT(" frame flags+body  (8-bit) length %" PRIu64, body_len_declared);
103           } else {
104                     header_len = 1 + 8; /* 0xFF, length */
105                     ND_PRINT(" frame flags+body (64-bit) length");
106                     ND_TCHECK_LEN(cp, header_len); /* 0xFF, length */
107                     body_len_declared = GET_BE_U_8(cp + 1);
108                     ND_PRINT(" %" PRIu64, body_len_declared);
109           }
110           if (body_len_declared == 0)
111                     return cp + header_len; /* skip to the next frame */
112           ND_TCHECK_LEN(cp, header_len + 1); /* ..., flags */
113           flags = GET_U_1(cp + header_len);
114 
115           body_len_captured = ep - cp - header_len;
116           if (body_len_declared > body_len_captured)
117                     ND_PRINT(" (%" PRIu64 " captured)", body_len_captured);
118           ND_PRINT(", flags 0x%02x", flags);
119 
120           if (ndo->ndo_vflag) {
121                     uint64_t body_len_printed = ND_MIN(body_len_captured, body_len_declared);
122 
123                     ND_PRINT(" (%s)", bittok2str(flags_bm, "none", flags));
124                     if (ndo->ndo_vflag == 1)
125                               body_len_printed = ND_MIN(VBYTES + 1, body_len_printed);
126                     if (body_len_printed > 1) {
127                               ND_PRINT(", first %" PRIu64 " byte(s) of body:", body_len_printed - 1);
128                               hex_and_ascii_print(ndo, "\n\t ", cp + header_len + 1, body_len_printed - 1);
129                     }
130           }
131 
132           /*
133            * Do not advance cp by the sum of header_len and body_len_declared
134            * before each offset has successfully passed ND_TCHECK_LEN() as the
135            * sum can roll over (9 + 0xfffffffffffffff7 = 0) and cause an
136            * infinite loop.
137            */
138           cp += header_len;
139           ND_TCHECK_LEN(cp, body_len_declared); /* Next frame within the buffer ? */
140           return cp + body_len_declared;
141 
142 trunc:
143           nd_trunc_longjmp(ndo);
144 }
145 
146 void
zmtp1_print(netdissect_options * ndo,const u_char * cp,u_int len)147 zmtp1_print(netdissect_options *ndo, const u_char *cp, u_int len)
148 {
149           const u_char *ep = ND_MIN(ndo->ndo_snapend, cp + len);
150 
151           ndo->ndo_protocol = "zmtp1";
152           ND_PRINT(": ZMTP/1.0");
153           while (cp < ep)
154                     cp = zmtp1_print_frame(ndo, cp, ep);
155 }
156 
157 /* The functions below decode a ZeroMQ datagram, supposedly stored in the "Data"
158  * field of an ODATA/RDATA [E]PGM packet. An excerpt from zmq_pgm(7) man page
159  * follows.
160  *
161  * In order for late joining consumers to be able to identify message
162  * boundaries, each PGM datagram payload starts with a 16-bit unsigned integer
163  * in network byte order specifying either the offset of the first message frame
164  * in the datagram or containing the value 0xFFFF if the datagram contains
165  * solely an intermediate part of a larger message.
166  *
167  * Note that offset specifies where the first message begins rather than the
168  * first message part. Thus, if there are trailing message parts at the
169  * beginning of the packet the offset ignores them and points to first initial
170  * message part in the packet.
171  */
172 
173 static const u_char *
zmtp1_print_intermediate_part(netdissect_options * ndo,const u_char * cp,const u_int len)174 zmtp1_print_intermediate_part(netdissect_options *ndo, const u_char *cp, const u_int len)
175 {
176           u_int frame_offset;
177           u_int remaining_len;
178 
179           frame_offset = GET_BE_U_2(cp);
180           ND_PRINT("\n\t frame offset 0x%04x", frame_offset);
181           cp += 2;
182           remaining_len = ND_BYTES_AVAILABLE_AFTER(cp); /* without the frame length */
183 
184           if (frame_offset == 0xFFFF)
185                     frame_offset = len - 2; /* always within the declared length */
186           else if (2 + frame_offset > len) {
187                     ND_PRINT(" (exceeds datagram declared length)");
188                     goto trunc;
189           }
190 
191           /* offset within declared length of the datagram */
192           if (frame_offset) {
193                     ND_PRINT("\n\t frame intermediate part, %u bytes", frame_offset);
194                     if (frame_offset > remaining_len)
195                               ND_PRINT(" (%u captured)", remaining_len);
196                     if (ndo->ndo_vflag) {
197                               u_int len_printed = ND_MIN(frame_offset, remaining_len);
198 
199                               if (ndo->ndo_vflag == 1)
200                                         len_printed = ND_MIN(VBYTES, len_printed);
201                               if (len_printed > 1) {
202                                         ND_PRINT(", first %u byte(s):", len_printed);
203                                         hex_and_ascii_print(ndo, "\n\t ", cp, len_printed);
204                               }
205                     }
206           }
207           return cp + frame_offset;
208 
209 trunc:
210           nd_trunc_longjmp(ndo);
211 }
212 
213 void
zmtp1_datagram_print(netdissect_options * ndo,const u_char * cp,const u_int len)214 zmtp1_datagram_print(netdissect_options *ndo, const u_char *cp, const u_int len)
215 {
216           const u_char *ep = ND_MIN(ndo->ndo_snapend, cp + len);
217 
218           ndo->ndo_protocol = "zmtp1";
219           cp = zmtp1_print_intermediate_part(ndo, cp, len);
220           while (cp < ep)
221                     cp = zmtp1_print_frame(ndo, cp, ep);
222 }
223