1: /* dnsmasq is Copyright (c) 2000-2021 Simon Kelley
2:
3: This program is free software; you can redistribute it and/or modify
4: it under the terms of the GNU General Public License as published by
5: the Free Software Foundation; version 2 dated June, 1991, or
6: (at your option) version 3 dated 29 June, 2007.
7:
8: This program is distributed in the hope that it will be useful,
9: but WITHOUT ANY WARRANTY; without even the implied warranty of
10: MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
11: GNU General Public License for more details.
12:
13: You should have received a copy of the GNU General Public License
14: along with this program. If not, see <http://www.gnu.org/licenses/>.
15: */
16:
17: #include "dnsmasq.h"
18:
19: #ifdef HAVE_DUMPFILE
20:
21: static u32 packet_count;
22:
23: /* https://wiki.wireshark.org/Development/LibpcapFileFormat */
24: struct pcap_hdr_s {
25: u32 magic_number; /* magic number */
26: u16 version_major; /* major version number */
27: u16 version_minor; /* minor version number */
28: u32 thiszone; /* GMT to local correction */
29: u32 sigfigs; /* accuracy of timestamps */
30: u32 snaplen; /* max length of captured packets, in octets */
31: u32 network; /* data link type */
32: };
33:
34: struct pcaprec_hdr_s {
35: u32 ts_sec; /* timestamp seconds */
36: u32 ts_usec; /* timestamp microseconds */
37: u32 incl_len; /* number of octets of packet saved in file */
38: u32 orig_len; /* actual length of packet */
39: };
40:
41:
42: void dump_init(void)
43: {
44: struct stat buf;
45: struct pcap_hdr_s header;
46: struct pcaprec_hdr_s pcap_header;
47:
48: packet_count = 0;
49:
50: if (stat(daemon->dump_file, &buf) == -1)
51: {
52: /* doesn't exist, create and add header */
53: header.magic_number = 0xa1b2c3d4;
54: header.version_major = 2;
55: header.version_minor = 4;
56: header.thiszone = 0;
57: header.sigfigs = 0;
58: header.snaplen = daemon->edns_pktsz + 200; /* slop for IP/UDP headers */
59: header.network = 101; /* DLT_RAW http://www.tcpdump.org/linktypes.html */
60:
61: if (errno != ENOENT ||
62: (daemon->dumpfd = creat(daemon->dump_file, S_IRUSR | S_IWUSR)) == -1 ||
63: !read_write(daemon->dumpfd, (void *)&header, sizeof(header), 0))
64: die(_("cannot create %s: %s"), daemon->dump_file, EC_FILE);
65: }
66: else if ((daemon->dumpfd = open(daemon->dump_file, O_APPEND | O_RDWR)) == -1 ||
67: !read_write(daemon->dumpfd, (void *)&header, sizeof(header), 1))
68: die(_("cannot access %s: %s"), daemon->dump_file, EC_FILE);
69: else if (header.magic_number != 0xa1b2c3d4)
70: die(_("bad header in %s"), daemon->dump_file, EC_FILE);
71: else
72: {
73: /* count existing records */
74: while (read_write(daemon->dumpfd, (void *)&pcap_header, sizeof(pcap_header), 1))
75: {
76: lseek(daemon->dumpfd, pcap_header.incl_len, SEEK_CUR);
77: packet_count++;
78: }
79: }
80: }
81:
82: void dump_packet(int mask, void *packet, size_t len, union mysockaddr *src, union mysockaddr *dst)
83: {
84: struct ip ip;
85: struct ip6_hdr ip6;
86: int family;
87: struct udphdr {
88: u16 uh_sport; /* source port */
89: u16 uh_dport; /* destination port */
90: u16 uh_ulen; /* udp length */
91: u16 uh_sum; /* udp checksum */
92: } udp;
93: struct pcaprec_hdr_s pcap_header;
94: struct timeval time;
95: u32 i, sum;
96: void *iphdr;
97: size_t ipsz;
98: int rc;
99:
100: if (daemon->dumpfd == -1 || !(mask & daemon->dump_mask))
101: return;
102:
103: /* So wireshark can Id the packet. */
104: udp.uh_sport = udp.uh_dport = htons(NAMESERVER_PORT);
105:
106: if (src)
107: family = src->sa.sa_family;
108: else
109: family = dst->sa.sa_family;
110:
111: if (family == AF_INET6)
112: {
113: iphdr = &ip6;
114: ipsz = sizeof(ip6);
115: memset(&ip6, 0, sizeof(ip6));
116:
117: ip6.ip6_vfc = 6 << 4;
118: ip6.ip6_plen = htons(sizeof(struct udphdr) + len);
119: ip6.ip6_nxt = IPPROTO_UDP;
120: ip6.ip6_hops = 64;
121:
122: if (src)
123: {
124: memcpy(&ip6.ip6_src, &src->in6.sin6_addr, IN6ADDRSZ);
125: udp.uh_sport = src->in6.sin6_port;
126: }
127:
128: if (dst)
129: {
130: memcpy(&ip6.ip6_dst, &dst->in6.sin6_addr, IN6ADDRSZ);
131: udp.uh_dport = dst->in6.sin6_port;
132: }
133:
134: /* start UDP checksum */
135: for (sum = 0, i = 0; i < IN6ADDRSZ; i+=2)
136: {
137: sum += ip6.ip6_src.s6_addr[i] + (ip6.ip6_src.s6_addr[i+1] << 8) ;
138: sum += ip6.ip6_dst.s6_addr[i] + (ip6.ip6_dst.s6_addr[i+1] << 8) ;
139:
140: }
141: }
142: else
143: {
144: iphdr = &ip;
145: ipsz = sizeof(ip);
146: memset(&ip, 0, sizeof(ip));
147:
148: ip.ip_v = IPVERSION;
149: ip.ip_hl = sizeof(struct ip) / 4;
150: ip.ip_len = htons(sizeof(struct ip) + sizeof(struct udphdr) + len);
151: ip.ip_ttl = IPDEFTTL;
152: ip.ip_p = IPPROTO_UDP;
153:
154: if (src)
155: {
156: ip.ip_src = src->in.sin_addr;
157: udp.uh_sport = src->in.sin_port;
158: }
159:
160: if (dst)
161: {
162: ip.ip_dst = dst->in.sin_addr;
163: udp.uh_dport = dst->in.sin_port;
164: }
165:
166: ip.ip_sum = 0;
167: for (sum = 0, i = 0; i < sizeof(struct ip) / 2; i++)
168: sum += ((u16 *)&ip)[i];
169: while (sum >> 16)
170: sum = (sum & 0xffff) + (sum >> 16);
171: ip.ip_sum = (sum == 0xffff) ? sum : ~sum;
172:
173: /* start UDP checksum */
174: sum = ip.ip_src.s_addr & 0xffff;
175: sum += (ip.ip_src.s_addr >> 16) & 0xffff;
176: sum += ip.ip_dst.s_addr & 0xffff;
177: sum += (ip.ip_dst.s_addr >> 16) & 0xffff;
178: }
179:
180: if (len & 1)
181: ((unsigned char *)packet)[len] = 0; /* for checksum, in case length is odd. */
182:
183: udp.uh_sum = 0;
184: udp.uh_ulen = htons(sizeof(struct udphdr) + len);
185: sum += htons(IPPROTO_UDP);
186: sum += htons(sizeof(struct udphdr) + len);
187: for (i = 0; i < sizeof(struct udphdr)/2; i++)
188: sum += ((u16 *)&udp)[i];
189: for (i = 0; i < (len + 1) / 2; i++)
190: sum += ((u16 *)packet)[i];
191: while (sum >> 16)
192: sum = (sum & 0xffff) + (sum >> 16);
193: udp.uh_sum = (sum == 0xffff) ? sum : ~sum;
194:
195: rc = gettimeofday(&time, NULL);
196: pcap_header.ts_sec = time.tv_sec;
197: pcap_header.ts_usec = time.tv_usec;
198: pcap_header.incl_len = pcap_header.orig_len = ipsz + sizeof(udp) + len;
199:
200: if (rc == -1 ||
201: !read_write(daemon->dumpfd, (void *)&pcap_header, sizeof(pcap_header), 0) ||
202: !read_write(daemon->dumpfd, iphdr, ipsz, 0) ||
203: !read_write(daemon->dumpfd, (void *)&udp, sizeof(udp), 0) ||
204: !read_write(daemon->dumpfd, (void *)packet, len, 0))
205: my_syslog(LOG_ERR, _("failed to write packet dump"));
206: else
207: my_syslog(LOG_INFO, _("dumping UDP packet %u mask 0x%04x"), ++packet_count, mask);
208:
209: }
210:
211: #endif
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