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: unsigned char *find_pseudoheader(struct dns_header *header, size_t plen, size_t *len, unsigned char **p, int *is_sign, int *is_last)
20: {
21: /* See if packet has an RFC2671 pseudoheader, and if so return a pointer to it.
22: also return length of pseudoheader in *len and pointer to the UDP size in *p
23: Finally, check to see if a packet is signed. If it is we cannot change a single bit before
24: forwarding. We look for TSIG in the addition section, and TKEY queries (for GSS-TSIG) */
25:
26: int i, arcount = ntohs(header->arcount);
27: unsigned char *ansp = (unsigned char *)(header+1);
28: unsigned short rdlen, type, class;
29: unsigned char *ret = NULL;
30:
31: if (is_sign)
32: {
33: *is_sign = 0;
34:
35: if (OPCODE(header) == QUERY)
36: {
37: for (i = ntohs(header->qdcount); i != 0; i--)
38: {
39: if (!(ansp = skip_name(ansp, header, plen, 4)))
40: return NULL;
41:
42: GETSHORT(type, ansp);
43: GETSHORT(class, ansp);
44:
45: if (class == C_IN && type == T_TKEY)
46: *is_sign = 1;
47: }
48: }
49: }
50: else
51: {
52: if (!(ansp = skip_questions(header, plen)))
53: return NULL;
54: }
55:
56: if (arcount == 0)
57: return NULL;
58:
59: if (!(ansp = skip_section(ansp, ntohs(header->ancount) + ntohs(header->nscount), header, plen)))
60: return NULL;
61:
62: for (i = 0; i < arcount; i++)
63: {
64: unsigned char *save, *start = ansp;
65: if (!(ansp = skip_name(ansp, header, plen, 10)))
66: return NULL;
67:
68: GETSHORT(type, ansp);
69: save = ansp;
70: GETSHORT(class, ansp);
71: ansp += 4; /* TTL */
72: GETSHORT(rdlen, ansp);
73: if (!ADD_RDLEN(header, ansp, plen, rdlen))
74: return NULL;
75: if (type == T_OPT)
76: {
77: if (len)
78: *len = ansp - start;
79:
80: if (p)
81: *p = save;
82:
83: if (is_last)
84: *is_last = (i == arcount-1);
85:
86: ret = start;
87: }
88: else if (is_sign &&
89: i == arcount - 1 &&
90: class == C_ANY &&
91: type == T_TSIG)
92: *is_sign = 1;
93: }
94:
95: return ret;
96: }
97:
98:
99: /* replace == 2 ->delete existing option only. */
100: size_t add_pseudoheader(struct dns_header *header, size_t plen, unsigned char *limit,
101: unsigned short udp_sz, int optno, unsigned char *opt, size_t optlen, int set_do, int replace)
102: {
103: unsigned char *lenp, *datap, *p, *udp_len, *buff = NULL;
104: int rdlen = 0, is_sign, is_last;
105: unsigned short flags = set_do ? 0x8000 : 0, rcode = 0;
106:
107: p = find_pseudoheader(header, plen, NULL, &udp_len, &is_sign, &is_last);
108:
109: if (is_sign)
110: return plen;
111:
112: if (p)
113: {
114: /* Existing header */
115: int i;
116: unsigned short code, len;
117:
118: p = udp_len;
119: GETSHORT(udp_sz, p);
120: GETSHORT(rcode, p);
121: GETSHORT(flags, p);
122:
123: if (set_do)
124: {
125: p -= 2;
126: flags |= 0x8000;
127: PUTSHORT(flags, p);
128: }
129:
130: lenp = p;
131: GETSHORT(rdlen, p);
132: if (!CHECK_LEN(header, p, plen, rdlen))
133: return plen; /* bad packet */
134: datap = p;
135:
136: /* no option to add */
137: if (optno == 0)
138: return plen;
139:
140: /* check if option already there */
141: for (i = 0; i + 4 < rdlen;)
142: {
143: GETSHORT(code, p);
144: GETSHORT(len, p);
145:
146: /* malformed option, delete the whole OPT RR and start again. */
147: if (i + 4 + len > rdlen)
148: {
149: rdlen = 0;
150: is_last = 0;
151: break;
152: }
153:
154: if (code == optno)
155: {
156: if (replace == 0)
157: return plen;
158:
159: /* delete option if we're to replace it. */
160: p -= 4;
161: rdlen -= len + 4;
162: memmove(p, p+len+4, rdlen - i);
163: PUTSHORT(rdlen, lenp);
164: lenp -= 2;
165: }
166: else
167: {
168: p += len;
169: i += len + 4;
170: }
171: }
172:
173: /* If we're going to extend the RR, it has to be the last RR in the packet */
174: if (!is_last)
175: {
176: /* First, take a copy of the options. */
177: if (rdlen != 0 && (buff = whine_malloc(rdlen)))
178: memcpy(buff, datap, rdlen);
179:
180: /* now, delete OPT RR */
181: plen = rrfilter(header, plen, 0);
182:
183: /* Now, force addition of a new one */
184: p = NULL;
185: }
186: }
187:
188: if (!p)
189: {
190: /* We are (re)adding the pseudoheader */
191: if (!(p = skip_questions(header, plen)) ||
192: !(p = skip_section(p,
193: ntohs(header->ancount) + ntohs(header->nscount) + ntohs(header->arcount),
194: header, plen)))
195: {
196: free(buff);
197: return plen;
198: }
199: if (p + 11 > limit)
200: {
201: free(buff);
202: return plen; /* Too big */
203: }
204: *p++ = 0; /* empty name */
205: PUTSHORT(T_OPT, p);
206: PUTSHORT(udp_sz, p); /* max packet length, 512 if not given in EDNS0 header */
207: PUTSHORT(rcode, p); /* extended RCODE and version */
208: PUTSHORT(flags, p); /* DO flag */
209: lenp = p;
210: PUTSHORT(rdlen, p); /* RDLEN */
211: datap = p;
212: /* Copy back any options */
213: if (buff)
214: {
215: if (p + rdlen > limit)
216: {
217: free(buff);
218: return plen; /* Too big */
219: }
220: memcpy(p, buff, rdlen);
221: free(buff);
222: p += rdlen;
223: }
224:
225: /* Only bump arcount if RR is going to fit */
226: if (((ssize_t)optlen) <= (limit - (p + 4)))
227: header->arcount = htons(ntohs(header->arcount) + 1);
228: }
229:
230: if (((ssize_t)optlen) > (limit - (p + 4)))
231: return plen; /* Too big */
232:
233: /* Add new option */
234: if (optno != 0 && replace != 2)
235: {
236: if (p + 4 > limit)
237: return plen; /* Too big */
238: PUTSHORT(optno, p);
239: PUTSHORT(optlen, p);
240: if (p + optlen > limit)
241: return plen; /* Too big */
242: memcpy(p, opt, optlen);
243: p += optlen;
244: PUTSHORT(p - datap, lenp);
245: }
246: return p - (unsigned char *)header;
247: }
248:
249: size_t add_do_bit(struct dns_header *header, size_t plen, unsigned char *limit)
250: {
251: return add_pseudoheader(header, plen, (unsigned char *)limit, PACKETSZ, 0, NULL, 0, 1, 0);
252: }
253:
254: static unsigned char char64(unsigned char c)
255: {
256: return "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/"[c & 0x3f];
257: }
258:
259: static void encoder(unsigned char *in, char *out)
260: {
261: out[0] = char64(in[0]>>2);
262: out[1] = char64((in[0]<<4) | (in[1]>>4));
263: out[2] = char64((in[1]<<2) | (in[2]>>6));
264: out[3] = char64(in[2]);
265: }
266:
267: static size_t add_dns_client(struct dns_header *header, size_t plen, unsigned char *limit,
268: union mysockaddr *l3, time_t now, int *cacheablep)
269: {
270: int maclen, replace = 2; /* can't get mac address, just delete any incoming. */
271: unsigned char mac[DHCP_CHADDR_MAX];
272: char encode[18]; /* handle 6 byte MACs */
273:
274: if ((maclen = find_mac(l3, mac, 1, now)) == 6)
275: {
276: replace = 1;
277: *cacheablep = 0;
278:
279: if (option_bool(OPT_MAC_HEX))
280: print_mac(encode, mac, maclen);
281: else
282: {
283: encoder(mac, encode);
284: encoder(mac+3, encode+4);
285: encode[8] = 0;
286: }
287: }
288:
289: return add_pseudoheader(header, plen, limit, PACKETSZ, EDNS0_OPTION_NOMDEVICEID, (unsigned char *)encode, strlen(encode), 0, replace);
290: }
291:
292:
293: static size_t add_mac(struct dns_header *header, size_t plen, unsigned char *limit,
294: union mysockaddr *l3, time_t now, int *cacheablep)
295: {
296: int maclen;
297: unsigned char mac[DHCP_CHADDR_MAX];
298:
299: if ((maclen = find_mac(l3, mac, 1, now)) != 0)
300: {
301: *cacheablep = 0;
302: plen = add_pseudoheader(header, plen, limit, PACKETSZ, EDNS0_OPTION_MAC, mac, maclen, 0, 0);
303: }
304:
305: return plen;
306: }
307:
308: struct subnet_opt {
309: u16 family;
310: u8 source_netmask, scope_netmask;
311: u8 addr[IN6ADDRSZ];
312: };
313:
314: static void *get_addrp(union mysockaddr *addr, const short family)
315: {
316: if (family == AF_INET6)
317: return &addr->in6.sin6_addr;
318:
319: return &addr->in.sin_addr;
320: }
321:
322: static size_t calc_subnet_opt(struct subnet_opt *opt, union mysockaddr *source, int *cacheablep)
323: {
324: /* http://tools.ietf.org/html/draft-vandergaast-edns-client-subnet-02 */
325:
326: int len;
327: void *addrp = NULL;
328: int sa_family = source->sa.sa_family;
329: int cacheable = 0;
330:
331: opt->source_netmask = 0;
332: opt->scope_netmask = 0;
333:
334: if (source->sa.sa_family == AF_INET6 && daemon->add_subnet6)
335: {
336: opt->source_netmask = daemon->add_subnet6->mask;
337: if (daemon->add_subnet6->addr_used)
338: {
339: sa_family = daemon->add_subnet6->addr.sa.sa_family;
340: addrp = get_addrp(&daemon->add_subnet6->addr, sa_family);
341: cacheable = 1;
342: }
343: else
344: addrp = &source->in6.sin6_addr;
345: }
346:
347: if (source->sa.sa_family == AF_INET && daemon->add_subnet4)
348: {
349: opt->source_netmask = daemon->add_subnet4->mask;
350: if (daemon->add_subnet4->addr_used)
351: {
352: sa_family = daemon->add_subnet4->addr.sa.sa_family;
353: addrp = get_addrp(&daemon->add_subnet4->addr, sa_family);
354: cacheable = 1; /* Address is constant */
355: }
356: else
357: addrp = &source->in.sin_addr;
358: }
359:
360: opt->family = htons(sa_family == AF_INET6 ? 2 : 1);
361:
362: if (addrp && opt->source_netmask != 0)
363: {
364: len = ((opt->source_netmask - 1) >> 3) + 1;
365: memcpy(opt->addr, addrp, len);
366: if (opt->source_netmask & 7)
367: opt->addr[len-1] &= 0xff << (8 - (opt->source_netmask & 7));
368: }
369: else
370: {
371: cacheable = 1; /* No address ever supplied. */
372: len = 0;
373: }
374:
375: if (cacheablep)
376: *cacheablep = cacheable;
377:
378: return len + 4;
379: }
380:
381: static size_t add_source_addr(struct dns_header *header, size_t plen, unsigned char *limit, union mysockaddr *source, int *cacheable)
382: {
383: /* http://tools.ietf.org/html/draft-vandergaast-edns-client-subnet-02 */
384:
385: int len;
386: struct subnet_opt opt;
387:
388: len = calc_subnet_opt(&opt, source, cacheable);
389: return add_pseudoheader(header, plen, (unsigned char *)limit, PACKETSZ, EDNS0_OPTION_CLIENT_SUBNET, (unsigned char *)&opt, len, 0, 0);
390: }
391:
392: int check_source(struct dns_header *header, size_t plen, unsigned char *pseudoheader, union mysockaddr *peer)
393: {
394: /* Section 9.2, Check that subnet option in reply matches. */
395:
396: int len, calc_len;
397: struct subnet_opt opt;
398: unsigned char *p;
399: int code, i, rdlen;
400:
401: calc_len = calc_subnet_opt(&opt, peer, NULL);
402:
403: if (!(p = skip_name(pseudoheader, header, plen, 10)))
404: return 1;
405:
406: p += 8; /* skip UDP length and RCODE */
407:
408: GETSHORT(rdlen, p);
409: if (!CHECK_LEN(header, p, plen, rdlen))
410: return 1; /* bad packet */
411:
412: /* check if option there */
413: for (i = 0; i + 4 < rdlen; i += len + 4)
414: {
415: GETSHORT(code, p);
416: GETSHORT(len, p);
417: if (code == EDNS0_OPTION_CLIENT_SUBNET)
418: {
419: /* make sure this doesn't mismatch. */
420: opt.scope_netmask = p[3];
421: if (len != calc_len || memcmp(p, &opt, len) != 0)
422: return 0;
423: }
424: p += len;
425: }
426:
427: return 1;
428: }
429:
430: /* Set *check_subnet if we add a client subnet option, which needs to checked
431: in the reply. Set *cacheable to zero if we add an option which the answer
432: may depend on. */
433: size_t add_edns0_config(struct dns_header *header, size_t plen, unsigned char *limit,
434: union mysockaddr *source, time_t now, int *check_subnet, int *cacheable)
435: {
436: *check_subnet = 0;
437: *cacheable = 1;
438:
439: if (option_bool(OPT_ADD_MAC))
440: plen = add_mac(header, plen, limit, source, now, cacheable);
441:
442: if (option_bool(OPT_MAC_B64) || option_bool(OPT_MAC_HEX))
443: plen = add_dns_client(header, plen, limit, source, now, cacheable);
444:
445: if (daemon->dns_client_id)
446: plen = add_pseudoheader(header, plen, limit, PACKETSZ, EDNS0_OPTION_NOMCPEID,
447: (unsigned char *)daemon->dns_client_id, strlen(daemon->dns_client_id), 0, 1);
448:
449: if (option_bool(OPT_CLIENT_SUBNET))
450: {
451: plen = add_source_addr(header, plen, limit, source, cacheable);
452: *check_subnet = 1;
453: }
454:
455: return plen;
456: }
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