1 From 25e63f1e56f5acdcf91893a1b92ad1e0f2f552d8 Mon Sep 17 00:00:00 2001
2 From: Simon Kelley <simon@thekelleys.org.uk>
3 Date: Wed, 25 Nov 2020 21:17:52 +0000
4 Subject: Handle caching with EDNS options better.
6 If we add the EDNS client subnet option, or the client's
7 MAC address, then the reply we get back may very depending on
8 that. Since the cache is ignorant of such things, it's not safe to
9 cache such replies. This patch determines when a dangerous EDNS
10 option is being added and disables caching.
12 Note that for much the same reason, we can't combine multiple
13 queries for the same question when dangerous EDNS options are
14 being added, and the code now handles that in the same way. This
15 query combining is required for security against cache poisoning,
16 so disabling the cache has a security function as well as a
21 src/edns0.c | 75 ++++++++++++++++++++++++++++++++-------------------
22 src/forward.c | 41 ++++++++++++++++++----------
23 4 files changed, 78 insertions(+), 45 deletions(-)
27 @@ -690,8 +690,8 @@ still marks the request so that no upstr
28 address information either. The default is zero for both IPv4 and
29 IPv6. Note that upstream nameservers may be configured to return
30 different results based on this information, but the dnsmasq cache
31 -does not take account. If a dnsmasq instance is configured such that
32 -different results may be encountered, caching should be disabled.
33 +does not take account. Caching is therefore disabled for such replies,
34 +unless the subnet address being added is constant.
40 @@ -644,6 +644,7 @@ struct hostsfile {
41 #define FREC_TEST_PKTSZ 256
42 #define FREC_HAS_EXTRADATA 512
43 #define FREC_HAS_PHEADER 1024
44 +#define FREC_NO_CACHE 2048
46 #define HASH_SIZE 32 /* SHA-256 digest size */
48 @@ -1628,7 +1629,7 @@ size_t add_pseudoheader(struct dns_heade
49 unsigned short udp_sz, int optno, unsigned char *opt, size_t optlen, int set_do, int replace);
50 size_t add_do_bit(struct dns_header *header, size_t plen, unsigned char *limit);
51 size_t add_edns0_config(struct dns_header *header, size_t plen, unsigned char *limit,
52 - union mysockaddr *source, time_t now, int *check_subnet);
53 + union mysockaddr *source, time_t now, int *check_subnet, int *cacheable);
54 int check_source(struct dns_header *header, size_t plen, unsigned char *pseudoheader, union mysockaddr *peer);
59 @@ -264,7 +264,8 @@ static void encoder(unsigned char *in, c
60 out[3] = char64(in[2]);
63 -static size_t add_dns_client(struct dns_header *header, size_t plen, unsigned char *limit, union mysockaddr *l3, time_t now)
64 +static size_t add_dns_client(struct dns_header *header, size_t plen, unsigned char *limit,
65 + union mysockaddr *l3, time_t now, int *cacheablep)
67 int maclen, replace = 2; /* can't get mac address, just delete any incoming. */
68 unsigned char mac[DHCP_CHADDR_MAX];
69 @@ -273,6 +274,7 @@ static size_t add_dns_client(struct dns_
70 if ((maclen = find_mac(l3, mac, 1, now)) == 6)
75 if (option_bool(OPT_MAC_HEX))
76 print_mac(encode, mac, maclen);
77 @@ -288,14 +290,18 @@ static size_t add_dns_client(struct dns_
81 -static size_t add_mac(struct dns_header *header, size_t plen, unsigned char *limit, union mysockaddr *l3, time_t now)
82 +static size_t add_mac(struct dns_header *header, size_t plen, unsigned char *limit,
83 + union mysockaddr *l3, time_t now, int *cacheablep)
86 unsigned char mac[DHCP_CHADDR_MAX];
88 if ((maclen = find_mac(l3, mac, 1, now)) != 0)
89 - plen = add_pseudoheader(header, plen, limit, PACKETSZ, EDNS0_OPTION_MAC, mac, maclen, 0, 0);
93 + plen = add_pseudoheader(header, plen, limit, PACKETSZ, EDNS0_OPTION_MAC, mac, maclen, 0, 0);
99 @@ -313,17 +319,18 @@ static void *get_addrp(union mysockaddr
100 return &addr->in.sin_addr;
103 -static size_t calc_subnet_opt(struct subnet_opt *opt, union mysockaddr *source)
104 +static size_t calc_subnet_opt(struct subnet_opt *opt, union mysockaddr *source, int *cacheablep)
106 /* http://tools.ietf.org/html/draft-vandergaast-edns-client-subnet-02 */
110 int sa_family = source->sa.sa_family;
114 opt->source_netmask = 0;
115 opt->scope_netmask = 0;
118 if (source->sa.sa_family == AF_INET6 && daemon->add_subnet6)
120 opt->source_netmask = daemon->add_subnet6->mask;
121 @@ -331,6 +338,7 @@ static size_t calc_subnet_opt(struct sub
123 sa_family = daemon->add_subnet6->addr.sa.sa_family;
124 addrp = get_addrp(&daemon->add_subnet6->addr, sa_family);
128 addrp = &source->in6.sin6_addr;
129 @@ -343,6 +351,7 @@ static size_t calc_subnet_opt(struct sub
131 sa_family = daemon->add_subnet4->addr.sa.sa_family;
132 addrp = get_addrp(&daemon->add_subnet4->addr, sa_family);
133 + cacheable = 1; /* Address is constant */
136 addrp = &source->in.sin_addr;
137 @@ -350,8 +359,6 @@ static size_t calc_subnet_opt(struct sub
139 opt->family = htons(sa_family == AF_INET6 ? 2 : 1);
143 if (addrp && opt->source_netmask != 0)
145 len = ((opt->source_netmask - 1) >> 3) + 1;
146 @@ -359,18 +366,26 @@ static size_t calc_subnet_opt(struct sub
147 if (opt->source_netmask & 7)
148 opt->addr[len-1] &= 0xff << (8 - (opt->source_netmask & 7));
152 + cacheable = 1; /* No address ever supplied. */
157 + *cacheablep = cacheable;
162 -static size_t add_source_addr(struct dns_header *header, size_t plen, unsigned char *limit, union mysockaddr *source)
163 +static size_t add_source_addr(struct dns_header *header, size_t plen, unsigned char *limit, union mysockaddr *source, int *cacheable)
165 /* http://tools.ietf.org/html/draft-vandergaast-edns-client-subnet-02 */
168 struct subnet_opt opt;
170 - len = calc_subnet_opt(&opt, source);
171 + len = calc_subnet_opt(&opt, source, cacheable);
172 return add_pseudoheader(header, plen, (unsigned char *)limit, PACKETSZ, EDNS0_OPTION_CLIENT_SUBNET, (unsigned char *)&opt, len, 0, 0);
175 @@ -383,18 +398,18 @@ int check_source(struct dns_header *head
179 - calc_len = calc_subnet_opt(&opt, peer);
181 - if (!(p = skip_name(pseudoheader, header, plen, 10)))
184 - p += 8; /* skip UDP length and RCODE */
185 + calc_len = calc_subnet_opt(&opt, peer, NULL);
187 - GETSHORT(rdlen, p);
188 - if (!CHECK_LEN(header, p, plen, rdlen))
189 - return 1; /* bad packet */
191 - /* check if option there */
192 + if (!(p = skip_name(pseudoheader, header, plen, 10)))
195 + p += 8; /* skip UDP length and RCODE */
197 + GETSHORT(rdlen, p);
198 + if (!CHECK_LEN(header, p, plen, rdlen))
199 + return 1; /* bad packet */
201 + /* check if option there */
202 for (i = 0; i + 4 < rdlen; i += len + 4)
205 @@ -412,24 +427,28 @@ int check_source(struct dns_header *head
209 +/* Set *check_subnet if we add a client subnet option, which needs to checked
210 + in the reply. Set *cacheable to zero if we add an option which the answer
212 size_t add_edns0_config(struct dns_header *header, size_t plen, unsigned char *limit,
213 - union mysockaddr *source, time_t now, int *check_subnet)
214 + union mysockaddr *source, time_t now, int *check_subnet, int *cacheable)
220 if (option_bool(OPT_ADD_MAC))
221 - plen = add_mac(header, plen, limit, source, now);
222 + plen = add_mac(header, plen, limit, source, now, cacheable);
224 if (option_bool(OPT_MAC_B64) || option_bool(OPT_MAC_HEX))
225 - plen = add_dns_client(header, plen, limit, source, now);
227 + plen = add_dns_client(header, plen, limit, source, now, cacheable);
229 if (daemon->dns_client_id)
230 plen = add_pseudoheader(header, plen, limit, PACKETSZ, EDNS0_OPTION_NOMCPEID,
231 (unsigned char *)daemon->dns_client_id, strlen(daemon->dns_client_id), 0, 1);
233 if (option_bool(OPT_CLIENT_SUBNET))
235 - plen = add_source_addr(header, plen, limit, source);
236 + plen = add_source_addr(header, plen, limit, source, cacheable);
242 @@ -344,13 +344,10 @@ static int forward_query(int udpfd, unio
244 /* Query from new source, but the same query may be in progress
245 from another source. If so, just add this client to the
246 - list that will get the reply.
247 + list that will get the reply.*/
249 - Note that is the EDNS client subnet option is in use, we can't do this,
250 - as the clients (and therefore query EDNS options) will be different
251 - for each query. The EDNS subnet code has checks to avoid
252 - attacks in this case. */
253 - if (!option_bool(OPT_CLIENT_SUBNET) && (forward = lookup_frec_by_query(hash, fwd_flags)))
254 + if (!option_bool(OPT_ADD_MAC) && !option_bool(OPT_MAC_B64) &&
255 + (forward = lookup_frec_by_query(hash, fwd_flags)))
257 /* Note whine_malloc() zeros memory. */
258 if (!daemon->free_frec_src &&
259 @@ -447,18 +444,21 @@ static int forward_query(int udpfd, unio
260 if (!flags && forward)
262 struct server *firstsentto = start;
263 - int subnet, forwarded = 0;
264 + int subnet, cacheable, forwarded = 0;
266 unsigned char *pheader;
268 /* If a query is retried, use the log_id for the retry when logging the answer. */
269 forward->frec_src.log_id = daemon->log_id;
271 - plen = add_edns0_config(header, plen, ((unsigned char *)header) + PACKETSZ, &forward->frec_src.source, now, &subnet);
272 + plen = add_edns0_config(header, plen, ((unsigned char *)header) + PACKETSZ, &forward->frec_src.source, now, &subnet, &cacheable);
275 forward->flags |= FREC_HAS_SUBNET;
279 + forward->flags |= FREC_NO_CACHE;
282 if (option_bool(OPT_DNSSEC_VALID) && do_dnssec)
284 @@ -642,7 +642,7 @@ static size_t process_reply(struct dns_h
290 if ((pheader = find_pseudoheader(header, n, &plen, &sizep, &is_sign, NULL)))
292 /* Get extended RCODE. */
293 @@ -1244,6 +1244,11 @@ void reply_query(int fd, int family, tim
294 header->hb4 |= HB4_CD;
296 header->hb4 &= ~HB4_CD;
298 + /* Never cache answers which are contingent on the source or MAC address EDSN0 option,
299 + since the cache is ignorant of such things. */
300 + if (forward->flags & FREC_NO_CACHE)
301 + no_cache_dnssec = 1;
303 if ((nn = process_reply(header, now, forward->sentto, (size_t)n, check_rebind, no_cache_dnssec, cache_secure, bogusanswer,
304 forward->flags & FREC_AD_QUESTION, forward->flags & FREC_DO_QUESTION,
305 @@ -1788,7 +1793,7 @@ unsigned char *tcp_request(int confd, ti
308 int checking_disabled, do_bit, added_pheader = 0, have_pseudoheader = 0;
309 - int check_subnet, no_cache_dnssec = 0, cache_secure = 0, bogusanswer = 0;
310 + int check_subnet, cacheable, no_cache_dnssec = 0, cache_secure = 0, bogusanswer = 0;
312 unsigned short qtype;
313 unsigned int gotname;
314 @@ -1959,7 +1964,7 @@ unsigned char *tcp_request(int confd, ti
316 unsigned char *oph = find_pseudoheader(header, size, NULL, NULL, NULL, NULL);
318 - size = add_edns0_config(header, size, ((unsigned char *) header) + 65536, &peer_addr, now, &check_subnet);
319 + size = add_edns0_config(header, size, ((unsigned char *) header) + 65536, &peer_addr, now, &check_subnet, &cacheable);
322 flags = search_servers(now, &addrp, gotname, daemon->namebuff, &type, &domain, &norebind);
323 @@ -2122,6 +2127,11 @@ unsigned char *tcp_request(int confd, ti
327 + /* Never cache answers which are contingent on the source or MAC address EDSN0 option,
328 + since the cache is ignorant of such things. */
330 + no_cache_dnssec = 1;
332 m = process_reply(header, now, last_server, (unsigned int)m,
333 option_bool(OPT_NO_REBIND) && !norebind, no_cache_dnssec, cache_secure, bogusanswer,
334 ad_reqd, do_bit, added_pheader, check_subnet, &peer_addr);
335 @@ -2385,10 +2395,13 @@ static struct frec *lookup_frec_by_query
338 /* FREC_DNSKEY and FREC_DS_QUERY are never set in flags, so the test below
339 - ensures that no frec created for internal DNSSEC query can be returned here. */
340 + ensures that no frec created for internal DNSSEC query can be returned here.
342 + Similarly FREC_NO_CACHE is never set in flags, so a query which is
343 + contigent on a particular source address EDNS0 option will never be matched. */
345 #define FLAGMASK (FREC_CHECKING_DISABLED | FREC_AD_QUESTION | FREC_DO_QUESTION \
346 - | FREC_HAS_PHEADER | FREC_DNSKEY_QUERY | FREC_DS_QUERY)
347 + | FREC_HAS_PHEADER | FREC_DNSKEY_QUERY | FREC_DS_QUERY | FREC_NO_CACHE)
349 for(f = daemon->frec_list; f; f = f->next)