diff options
Diffstat (limited to 'src/resolve/resolved-dns-cache.c')
| -rw-r--r-- | src/resolve/resolved-dns-cache.c | 1371 |
1 files changed, 1371 insertions, 0 deletions
diff --git a/src/resolve/resolved-dns-cache.c b/src/resolve/resolved-dns-cache.c new file mode 100644 index 0000000..d9e1053 --- /dev/null +++ b/src/resolve/resolved-dns-cache.c @@ -0,0 +1,1371 @@ +/* SPDX-License-Identifier: LGPL-2.1-or-later */ + +#include <net/if.h> + +#include "af-list.h" +#include "alloc-util.h" +#include "dns-domain.h" +#include "format-util.h" +#include "resolved-dns-answer.h" +#include "resolved-dns-cache.h" +#include "resolved-dns-packet.h" +#include "string-util.h" + +/* Never cache more than 4K entries. RFC 1536, Section 5 suggests to + * leave DNS caches unbounded, but that's crazy. */ +#define CACHE_MAX 4096 + +/* We never keep any item longer than 2h in our cache */ +#define CACHE_TTL_MAX_USEC (2 * USEC_PER_HOUR) + +/* How long to cache strange rcodes, i.e. rcodes != SUCCESS and != NXDOMAIN (specifically: that's only SERVFAIL for + * now) */ +#define CACHE_TTL_STRANGE_RCODE_USEC (10 * USEC_PER_SEC) + +#define CACHEABLE_QUERY_FLAGS (SD_RESOLVED_AUTHENTICATED|SD_RESOLVED_CONFIDENTIAL) + +typedef enum DnsCacheItemType DnsCacheItemType; +typedef struct DnsCacheItem DnsCacheItem; + +enum DnsCacheItemType { + DNS_CACHE_POSITIVE, + DNS_CACHE_NODATA, + DNS_CACHE_NXDOMAIN, + DNS_CACHE_RCODE, /* "strange" RCODE (effective only SERVFAIL for now) */ +}; + +struct DnsCacheItem { + DnsCacheItemType type; + int rcode; + DnsResourceKey *key; /* The key for this item, i.e. the lookup key */ + DnsResourceRecord *rr; /* The RR for this item, i.e. the lookup value for positive queries */ + DnsAnswer *answer; /* The full validated answer, if this is an RRset acquired via a "primary" lookup */ + DnsPacket *full_packet; /* The full packet this information was acquired with */ + + usec_t until; + uint64_t query_flags; /* SD_RESOLVED_AUTHENTICATED and/or SD_RESOLVED_CONFIDENTIAL */ + DnssecResult dnssec_result; + + int ifindex; + int owner_family; + union in_addr_union owner_address; + + unsigned prioq_idx; + LIST_FIELDS(DnsCacheItem, by_key); + + bool shared_owner; +}; + +/* Returns true if this is a cache item created as result of an explicit lookup, or created as "side-effect" + * of another request. "Primary" entries will carry the full answer data (with NSEC, …) that can aso prove + * wildcard expansion, non-existence and such, while entries that were created as "side-effect" just contain + * immediate RR data for the specified RR key, but nothing else. */ +#define DNS_CACHE_ITEM_IS_PRIMARY(item) (!!(item)->answer) + +static const char *dns_cache_item_type_to_string(DnsCacheItem *item) { + assert(item); + + switch (item->type) { + + case DNS_CACHE_POSITIVE: + return "POSITIVE"; + + case DNS_CACHE_NODATA: + return "NODATA"; + + case DNS_CACHE_NXDOMAIN: + return "NXDOMAIN"; + + case DNS_CACHE_RCODE: + return dns_rcode_to_string(item->rcode); + } + + return NULL; +} + +static DnsCacheItem* dns_cache_item_free(DnsCacheItem *i) { + if (!i) + return NULL; + + dns_resource_record_unref(i->rr); + dns_resource_key_unref(i->key); + dns_answer_unref(i->answer); + dns_packet_unref(i->full_packet); + return mfree(i); +} +DEFINE_TRIVIAL_CLEANUP_FUNC(DnsCacheItem*, dns_cache_item_free); + +static void dns_cache_item_unlink_and_free(DnsCache *c, DnsCacheItem *i) { + DnsCacheItem *first; + + assert(c); + + if (!i) + return; + + first = hashmap_get(c->by_key, i->key); + LIST_REMOVE(by_key, first, i); + + if (first) + assert_se(hashmap_replace(c->by_key, first->key, first) >= 0); + else + hashmap_remove(c->by_key, i->key); + + prioq_remove(c->by_expiry, i, &i->prioq_idx); + + dns_cache_item_free(i); +} + +static bool dns_cache_remove_by_rr(DnsCache *c, DnsResourceRecord *rr) { + DnsCacheItem *first; + int r; + + first = hashmap_get(c->by_key, rr->key); + LIST_FOREACH(by_key, i, first) { + r = dns_resource_record_equal(i->rr, rr); + if (r < 0) + return r; + if (r > 0) { + dns_cache_item_unlink_and_free(c, i); + return true; + } + } + + return false; +} + +static bool dns_cache_remove_by_key(DnsCache *c, DnsResourceKey *key) { + DnsCacheItem *first; + + assert(c); + assert(key); + + first = hashmap_remove(c->by_key, key); + if (!first) + return false; + + LIST_FOREACH(by_key, i, first) { + prioq_remove(c->by_expiry, i, &i->prioq_idx); + dns_cache_item_free(i); + } + + return true; +} + +void dns_cache_flush(DnsCache *c) { + DnsResourceKey *key; + + assert(c); + + while ((key = hashmap_first_key(c->by_key))) + dns_cache_remove_by_key(c, key); + + assert(hashmap_size(c->by_key) == 0); + assert(prioq_size(c->by_expiry) == 0); + + c->by_key = hashmap_free(c->by_key); + c->by_expiry = prioq_free(c->by_expiry); +} + +static void dns_cache_make_space(DnsCache *c, unsigned add) { + assert(c); + + if (add <= 0) + return; + + /* Makes space for n new entries. Note that we actually allow + * the cache to grow beyond CACHE_MAX, but only when we shall + * add more RRs to the cache than CACHE_MAX at once. In that + * case the cache will be emptied completely otherwise. */ + + for (;;) { + _cleanup_(dns_resource_key_unrefp) DnsResourceKey *key = NULL; + DnsCacheItem *i; + + if (prioq_size(c->by_expiry) <= 0) + break; + + if (prioq_size(c->by_expiry) + add < CACHE_MAX) + break; + + i = prioq_peek(c->by_expiry); + assert(i); + + /* Take an extra reference to the key so that it + * doesn't go away in the middle of the remove call */ + key = dns_resource_key_ref(i->key); + dns_cache_remove_by_key(c, key); + } +} + +void dns_cache_prune(DnsCache *c) { + usec_t t = 0; + + assert(c); + + /* Remove all entries that are past their TTL */ + + for (;;) { + DnsCacheItem *i; + char key_str[DNS_RESOURCE_KEY_STRING_MAX]; + + i = prioq_peek(c->by_expiry); + if (!i) + break; + + if (t <= 0) + t = now(CLOCK_BOOTTIME); + + if (i->until > t) + break; + + /* Depending whether this is an mDNS shared entry + * either remove only this one RR or the whole RRset */ + log_debug("Removing %scache entry for %s (expired "USEC_FMT"s ago)", + i->shared_owner ? "shared " : "", + dns_resource_key_to_string(i->key, key_str, sizeof key_str), + (t - i->until) / USEC_PER_SEC); + + if (i->shared_owner) + dns_cache_item_unlink_and_free(c, i); + else { + _cleanup_(dns_resource_key_unrefp) DnsResourceKey *key = NULL; + + /* Take an extra reference to the key so that it + * doesn't go away in the middle of the remove call */ + key = dns_resource_key_ref(i->key); + dns_cache_remove_by_key(c, key); + } + } +} + +static int dns_cache_item_prioq_compare_func(const void *a, const void *b) { + const DnsCacheItem *x = a, *y = b; + + return CMP(x->until, y->until); +} + +static int dns_cache_init(DnsCache *c) { + int r; + + assert(c); + + r = prioq_ensure_allocated(&c->by_expiry, dns_cache_item_prioq_compare_func); + if (r < 0) + return r; + + r = hashmap_ensure_allocated(&c->by_key, &dns_resource_key_hash_ops); + if (r < 0) + return r; + + return r; +} + +static int dns_cache_link_item(DnsCache *c, DnsCacheItem *i) { + DnsCacheItem *first; + int r; + + assert(c); + assert(i); + + r = prioq_put(c->by_expiry, i, &i->prioq_idx); + if (r < 0) + return r; + + first = hashmap_get(c->by_key, i->key); + if (first) { + _unused_ _cleanup_(dns_resource_key_unrefp) DnsResourceKey *k = NULL; + + /* Keep a reference to the original key, while we manipulate the list. */ + k = dns_resource_key_ref(first->key); + + /* Now, try to reduce the number of keys we keep */ + dns_resource_key_reduce(&first->key, &i->key); + + if (first->rr) + dns_resource_key_reduce(&first->rr->key, &i->key); + if (i->rr) + dns_resource_key_reduce(&i->rr->key, &i->key); + + LIST_PREPEND(by_key, first, i); + assert_se(hashmap_replace(c->by_key, first->key, first) >= 0); + } else { + r = hashmap_put(c->by_key, i->key, i); + if (r < 0) { + prioq_remove(c->by_expiry, i, &i->prioq_idx); + return r; + } + } + + return 0; +} + +static DnsCacheItem* dns_cache_get(DnsCache *c, DnsResourceRecord *rr) { + assert(c); + assert(rr); + + LIST_FOREACH(by_key, i, (DnsCacheItem*) hashmap_get(c->by_key, rr->key)) + if (i->rr && dns_resource_record_equal(i->rr, rr) > 0) + return i; + + return NULL; +} + +static usec_t calculate_until( + DnsResourceRecord *rr, + uint32_t min_ttl, + uint32_t nsec_ttl, + usec_t timestamp, + bool use_soa_minimum) { + + uint32_t ttl; + usec_t u; + + assert(rr); + + ttl = MIN(min_ttl, nsec_ttl); + if (rr->key->type == DNS_TYPE_SOA && use_soa_minimum) { + /* If this is a SOA RR, and it is requested, clamp to the SOA's minimum field. This is used + * when we do negative caching, to determine the TTL for the negative caching entry. See RFC + * 2308, Section 5. */ + + if (ttl > rr->soa.minimum) + ttl = rr->soa.minimum; + } + + u = ttl * USEC_PER_SEC; + if (u > CACHE_TTL_MAX_USEC) + u = CACHE_TTL_MAX_USEC; + + if (rr->expiry != USEC_INFINITY) { + usec_t left; + + /* Make use of the DNSSEC RRSIG expiry info, if we have it */ + + left = LESS_BY(rr->expiry, now(CLOCK_REALTIME)); + if (u > left) + u = left; + } + + return timestamp + u; +} + +static void dns_cache_item_update_positive( + DnsCache *c, + DnsCacheItem *i, + DnsResourceRecord *rr, + DnsAnswer *answer, + DnsPacket *full_packet, + uint32_t min_ttl, + uint64_t query_flags, + bool shared_owner, + DnssecResult dnssec_result, + usec_t timestamp, + int ifindex, + int owner_family, + const union in_addr_union *owner_address) { + + assert(c); + assert(i); + assert(rr); + assert(owner_address); + + i->type = DNS_CACHE_POSITIVE; + + if (!i->by_key_prev) + /* We are the first item in the list, we need to + * update the key used in the hashmap */ + + assert_se(hashmap_replace(c->by_key, rr->key, i) >= 0); + + DNS_RR_REPLACE(i->rr, dns_resource_record_ref(rr)); + + DNS_RESOURCE_KEY_REPLACE(i->key, dns_resource_key_ref(rr->key)); + + DNS_ANSWER_REPLACE(i->answer, dns_answer_ref(answer)); + + DNS_PACKET_REPLACE(i->full_packet, dns_packet_ref(full_packet)); + + i->until = calculate_until(rr, min_ttl, UINT32_MAX, timestamp, false); + i->query_flags = query_flags & CACHEABLE_QUERY_FLAGS; + i->shared_owner = shared_owner; + i->dnssec_result = dnssec_result; + + i->ifindex = ifindex; + + i->owner_family = owner_family; + i->owner_address = *owner_address; + + prioq_reshuffle(c->by_expiry, i, &i->prioq_idx); +} + +static int dns_cache_put_positive( + DnsCache *c, + DnsProtocol protocol, + DnsResourceRecord *rr, + DnsAnswer *answer, + DnsPacket *full_packet, + uint64_t query_flags, + bool shared_owner, + DnssecResult dnssec_result, + usec_t timestamp, + int ifindex, + int owner_family, + const union in_addr_union *owner_address) { + + char key_str[DNS_RESOURCE_KEY_STRING_MAX]; + DnsCacheItem *existing; + uint32_t min_ttl; + int r; + + assert(c); + assert(rr); + assert(owner_address); + + /* Never cache pseudo RRs */ + if (dns_class_is_pseudo(rr->key->class)) + return 0; + if (dns_type_is_pseudo(rr->key->type)) + return 0; + + /* Determine the minimal TTL of all RRs in the answer plus the one by the main RR we are supposed to + * cache. Since we cache whole answers to questions we should never return answers where only some + * RRs are still valid, hence find the lowest here */ + min_ttl = MIN(dns_answer_min_ttl(answer), rr->ttl); + + /* New TTL is 0? Delete this specific entry... */ + if (min_ttl <= 0) { + r = dns_cache_remove_by_rr(c, rr); + log_debug("%s: %s", + r > 0 ? "Removed zero TTL entry from cache" : "Not caching zero TTL cache entry", + dns_resource_key_to_string(rr->key, key_str, sizeof key_str)); + return 0; + } + + /* Entry exists already? Update TTL, timestamp and owner */ + existing = dns_cache_get(c, rr); + if (existing) { + dns_cache_item_update_positive( + c, + existing, + rr, + answer, + full_packet, + min_ttl, + query_flags, + shared_owner, + dnssec_result, + timestamp, + ifindex, + owner_family, + owner_address); + return 0; + } + + /* Do not cache mDNS goodbye packet. */ + if (protocol == DNS_PROTOCOL_MDNS && rr->ttl <= 1) + return 0; + + /* Otherwise, add the new RR */ + r = dns_cache_init(c); + if (r < 0) + return r; + + dns_cache_make_space(c, 1); + + _cleanup_(dns_cache_item_freep) DnsCacheItem *i = new(DnsCacheItem, 1); + if (!i) + return -ENOMEM; + + *i = (DnsCacheItem) { + .type = DNS_CACHE_POSITIVE, + .key = dns_resource_key_ref(rr->key), + .rr = dns_resource_record_ref(rr), + .answer = dns_answer_ref(answer), + .full_packet = dns_packet_ref(full_packet), + .until = calculate_until(rr, min_ttl, UINT32_MAX, timestamp, false), + .query_flags = query_flags & CACHEABLE_QUERY_FLAGS, + .shared_owner = shared_owner, + .dnssec_result = dnssec_result, + .ifindex = ifindex, + .owner_family = owner_family, + .owner_address = *owner_address, + .prioq_idx = PRIOQ_IDX_NULL, + }; + + r = dns_cache_link_item(c, i); + if (r < 0) + return r; + + log_debug("Added positive %s %s%s cache entry for %s "USEC_FMT"s on %s/%s/%s", + FLAGS_SET(i->query_flags, SD_RESOLVED_AUTHENTICATED) ? "authenticated" : "unauthenticated", + FLAGS_SET(i->query_flags, SD_RESOLVED_CONFIDENTIAL) ? "confidential" : "non-confidential", + i->shared_owner ? " shared" : "", + dns_resource_key_to_string(i->key, key_str, sizeof key_str), + (i->until - timestamp) / USEC_PER_SEC, + i->ifindex == 0 ? "*" : FORMAT_IFNAME(i->ifindex), + af_to_name_short(i->owner_family), + IN_ADDR_TO_STRING(i->owner_family, &i->owner_address)); + + TAKE_PTR(i); + return 0; +} + +static int dns_cache_put_negative( + DnsCache *c, + DnsResourceKey *key, + int rcode, + DnsAnswer *answer, + DnsPacket *full_packet, + uint64_t query_flags, + DnssecResult dnssec_result, + uint32_t nsec_ttl, + usec_t timestamp, + DnsResourceRecord *soa, + int owner_family, + const union in_addr_union *owner_address) { + + _cleanup_(dns_cache_item_freep) DnsCacheItem *i = NULL; + char key_str[DNS_RESOURCE_KEY_STRING_MAX]; + int r; + + assert(c); + assert(key); + assert(owner_address); + + /* Never cache pseudo RR keys. DNS_TYPE_ANY is particularly + * important to filter out as we use this as a pseudo-type for + * NXDOMAIN entries */ + if (dns_class_is_pseudo(key->class)) + return 0; + if (dns_type_is_pseudo(key->type)) + return 0; + + if (IN_SET(rcode, DNS_RCODE_SUCCESS, DNS_RCODE_NXDOMAIN)) { + if (!soa) + return 0; + + /* For negative replies, check if we have a TTL of a SOA */ + if (nsec_ttl <= 0 || soa->soa.minimum <= 0 || soa->ttl <= 0) { + log_debug("Not caching negative entry with zero SOA/NSEC/NSEC3 TTL: %s", + dns_resource_key_to_string(key, key_str, sizeof key_str)); + return 0; + } + } else if (rcode != DNS_RCODE_SERVFAIL) + return 0; + + r = dns_cache_init(c); + if (r < 0) + return r; + + dns_cache_make_space(c, 1); + + i = new(DnsCacheItem, 1); + if (!i) + return -ENOMEM; + + *i = (DnsCacheItem) { + .type = + rcode == DNS_RCODE_SUCCESS ? DNS_CACHE_NODATA : + rcode == DNS_RCODE_NXDOMAIN ? DNS_CACHE_NXDOMAIN : DNS_CACHE_RCODE, + .query_flags = query_flags & CACHEABLE_QUERY_FLAGS, + .dnssec_result = dnssec_result, + .owner_family = owner_family, + .owner_address = *owner_address, + .prioq_idx = PRIOQ_IDX_NULL, + .rcode = rcode, + .answer = dns_answer_ref(answer), + .full_packet = dns_packet_ref(full_packet), + }; + + /* Determine how long to cache this entry. In case we have some RRs in the answer use the lowest TTL + * of any of them. Typically that's the SOA's TTL, which is OK, but could possibly be lower because + * of some other RR. Let's better take the lowest option here than a needlessly high one */ + i->until = + i->type == DNS_CACHE_RCODE ? timestamp + CACHE_TTL_STRANGE_RCODE_USEC : + calculate_until(soa, dns_answer_min_ttl(answer), nsec_ttl, timestamp, true); + + if (i->type == DNS_CACHE_NXDOMAIN) { + /* NXDOMAIN entries should apply equally to all types, so we use ANY as + * a pseudo type for this purpose here. */ + i->key = dns_resource_key_new(key->class, DNS_TYPE_ANY, dns_resource_key_name(key)); + if (!i->key) + return -ENOMEM; + + /* Make sure to remove any previous entry for this + * specific ANY key. (For non-ANY keys the cache data + * is already cleared by the caller.) Note that we + * don't bother removing positive or NODATA cache + * items in this case, because it would either be slow + * or require explicit indexing by name */ + dns_cache_remove_by_key(c, key); + } else + i->key = dns_resource_key_ref(key); + + r = dns_cache_link_item(c, i); + if (r < 0) + return r; + + log_debug("Added %s cache entry for %s "USEC_FMT"s", + dns_cache_item_type_to_string(i), + dns_resource_key_to_string(i->key, key_str, sizeof key_str), + (i->until - timestamp) / USEC_PER_SEC); + + i = NULL; + return 0; +} + +static void dns_cache_remove_previous( + DnsCache *c, + DnsResourceKey *key, + DnsAnswer *answer) { + + DnsResourceRecord *rr; + DnsAnswerFlags flags; + + assert(c); + + /* First, if we were passed a key (i.e. on LLMNR/DNS, but + * not on mDNS), delete all matching old RRs, so that we only + * keep complete by_key in place. */ + if (key) + dns_cache_remove_by_key(c, key); + + /* Second, flush all entries matching the answer, unless this + * is an RR that is explicitly marked to be "shared" between + * peers (i.e. mDNS RRs without the flush-cache bit set). */ + DNS_ANSWER_FOREACH_FLAGS(rr, flags, answer) { + if ((flags & DNS_ANSWER_CACHEABLE) == 0) + continue; + + if (flags & DNS_ANSWER_SHARED_OWNER) + continue; + + dns_cache_remove_by_key(c, rr->key); + } +} + +static bool rr_eligible(DnsResourceRecord *rr) { + assert(rr); + + /* When we see an NSEC/NSEC3 RR, we'll only cache it if it is from the lower zone, not the upper zone, since + * that's where the interesting bits are (with exception of DS RRs). Of course, this way we cannot derive DS + * existence from any cached NSEC/NSEC3, but that should be fine. */ + + switch (rr->key->type) { + + case DNS_TYPE_NSEC: + return !bitmap_isset(rr->nsec.types, DNS_TYPE_NS) || + bitmap_isset(rr->nsec.types, DNS_TYPE_SOA); + + case DNS_TYPE_NSEC3: + return !bitmap_isset(rr->nsec3.types, DNS_TYPE_NS) || + bitmap_isset(rr->nsec3.types, DNS_TYPE_SOA); + + default: + return true; + } +} + +int dns_cache_put( + DnsCache *c, + DnsCacheMode cache_mode, + DnsProtocol protocol, + DnsResourceKey *key, + int rcode, + DnsAnswer *answer, + DnsPacket *full_packet, + uint64_t query_flags, + DnssecResult dnssec_result, + uint32_t nsec_ttl, + int owner_family, + const union in_addr_union *owner_address) { + + DnsResourceRecord *soa = NULL; + bool weird_rcode = false; + DnsAnswerItem *item; + DnsAnswerFlags flags; + unsigned cache_keys; + usec_t timestamp; + int r; + + assert(c); + assert(owner_address); + + dns_cache_remove_previous(c, key, answer); + + /* We only care for positive replies and NXDOMAINs, on all other replies we will simply flush the respective + * entries, and that's it. (Well, with one further exception: since some DNS zones (akamai!) return SERVFAIL + * consistently for some lookups, and forwarders tend to propagate that we'll cache that too, but only for a + * short time.) */ + + if (IN_SET(rcode, DNS_RCODE_SUCCESS, DNS_RCODE_NXDOMAIN)) { + if (dns_answer_isempty(answer)) { + if (key) { + char key_str[DNS_RESOURCE_KEY_STRING_MAX]; + + log_debug("Not caching negative entry without a SOA record: %s", + dns_resource_key_to_string(key, key_str, sizeof key_str)); + } + + return 0; + } + + } else { + /* Only cache SERVFAIL as "weird" rcode for now. We can add more later, should that turn out to be + * beneficial. */ + if (rcode != DNS_RCODE_SERVFAIL) + return 0; + + weird_rcode = true; + } + + cache_keys = dns_answer_size(answer); + if (key) + cache_keys++; + + /* Make some space for our new entries */ + dns_cache_make_space(c, cache_keys); + + timestamp = now(CLOCK_BOOTTIME); + + /* Second, add in positive entries for all contained RRs */ + DNS_ANSWER_FOREACH_ITEM(item, answer) { + int primary = false; + + if (!FLAGS_SET(item->flags, DNS_ANSWER_CACHEABLE) || + !rr_eligible(item->rr)) + continue; + + if (key) { + /* We store the auxiliary RRs and packet data in the cache only if they were in + * direct response to the original query. If we cache an RR we also received, and + * that is just auxiliary information we can't use the data, hence don't. */ + + primary = dns_resource_key_match_rr(key, item->rr, NULL); + if (primary < 0) + return primary; + if (primary == 0) { + primary = dns_resource_key_match_cname_or_dname(key, item->rr->key, NULL); + if (primary < 0) + return primary; + } + } + + if (!primary) { + DnsCacheItem *first; + + /* Do not replace existing cache items for primary lookups with non-primary + * data. After all the primary lookup data is a lot more useful. */ + first = hashmap_get(c->by_key, item->rr->key); + if (first && DNS_CACHE_ITEM_IS_PRIMARY(first)) + return 0; + } + + r = dns_cache_put_positive( + c, + protocol, + item->rr, + primary ? answer : NULL, + primary ? full_packet : NULL, + ((item->flags & DNS_ANSWER_AUTHENTICATED) ? SD_RESOLVED_AUTHENTICATED : 0) | + (query_flags & SD_RESOLVED_CONFIDENTIAL), + item->flags & DNS_ANSWER_SHARED_OWNER, + dnssec_result, + timestamp, + item->ifindex, + owner_family, + owner_address); + if (r < 0) + goto fail; + } + + if (!key) /* mDNS doesn't know negative caching, really */ + return 0; + + /* Third, add in negative entries if the key has no RR */ + r = dns_answer_match_key(answer, key, NULL); + if (r < 0) + goto fail; + if (r > 0) + return 0; + + /* But not if it has a matching CNAME/DNAME (the negative caching will be done on the canonical name, + * not on the alias) */ + r = dns_answer_find_cname_or_dname(answer, key, NULL, NULL); + if (r < 0) + goto fail; + if (r > 0) + return 0; + + /* See https://tools.ietf.org/html/rfc2308, which say that a matching SOA record in the packet is used to + * enable negative caching. We apply one exception though: if we are about to cache a weird rcode we do so + * regardless of a SOA. */ + r = dns_answer_find_soa(answer, key, &soa, &flags); + if (r < 0) + goto fail; + if (r == 0 && !weird_rcode) + return 0; + if (r > 0) { + /* Refuse using the SOA data if it is unsigned, but the key is signed */ + if (FLAGS_SET(query_flags, SD_RESOLVED_AUTHENTICATED) && + (flags & DNS_ANSWER_AUTHENTICATED) == 0) + return 0; + } + + if (cache_mode == DNS_CACHE_MODE_NO_NEGATIVE) { + char key_str[DNS_RESOURCE_KEY_STRING_MAX]; + log_debug("Not caching negative entry for: %s, cache mode set to no-negative", + dns_resource_key_to_string(key, key_str, sizeof key_str)); + return 0; + } + + r = dns_cache_put_negative( + c, + key, + rcode, + answer, + full_packet, + query_flags, + dnssec_result, + nsec_ttl, + timestamp, + soa, + owner_family, owner_address); + if (r < 0) + goto fail; + + return 0; + +fail: + /* Adding all RRs failed. Let's clean up what we already + * added, just in case */ + + if (key) + dns_cache_remove_by_key(c, key); + + DNS_ANSWER_FOREACH_ITEM(item, answer) { + if ((item->flags & DNS_ANSWER_CACHEABLE) == 0) + continue; + + dns_cache_remove_by_key(c, item->rr->key); + } + + return r; +} + +static DnsCacheItem *dns_cache_get_by_key_follow_cname_dname_nsec(DnsCache *c, DnsResourceKey *k) { + DnsCacheItem *i; + const char *n; + int r; + + assert(c); + assert(k); + + /* If we hit some OOM error, or suchlike, we don't care too + * much, after all this is just a cache */ + + i = hashmap_get(c->by_key, k); + if (i) + return i; + + n = dns_resource_key_name(k); + + /* Check if we have an NXDOMAIN cache item for the name, notice that we use + * the pseudo-type ANY for NXDOMAIN cache items. */ + i = hashmap_get(c->by_key, &DNS_RESOURCE_KEY_CONST(k->class, DNS_TYPE_ANY, n)); + if (i && i->type == DNS_CACHE_NXDOMAIN) + return i; + + if (dns_type_may_redirect(k->type)) { + /* Check if we have a CNAME record instead */ + i = hashmap_get(c->by_key, &DNS_RESOURCE_KEY_CONST(k->class, DNS_TYPE_CNAME, n)); + if (i && i->type != DNS_CACHE_NODATA) + return i; + + /* OK, let's look for cached DNAME records. */ + for (;;) { + if (isempty(n)) + return NULL; + + i = hashmap_get(c->by_key, &DNS_RESOURCE_KEY_CONST(k->class, DNS_TYPE_DNAME, n)); + if (i && i->type != DNS_CACHE_NODATA) + return i; + + /* Jump one label ahead */ + r = dns_name_parent(&n); + if (r <= 0) + return NULL; + } + } + + if (k->type != DNS_TYPE_NSEC) { + /* Check if we have an NSEC record instead for the name. */ + i = hashmap_get(c->by_key, &DNS_RESOURCE_KEY_CONST(k->class, DNS_TYPE_NSEC, n)); + if (i) + return i; + } + + return NULL; +} + +static int answer_add_clamp_ttl( + DnsAnswer **answer, + DnsResourceRecord *rr, + int ifindex, + DnsAnswerFlags answer_flags, + DnsResourceRecord *rrsig, + uint64_t query_flags, + usec_t until, + usec_t current) { + + _cleanup_(dns_resource_record_unrefp) DnsResourceRecord *patched = NULL, *patched_rrsig = NULL; + int r; + + assert(answer); + assert(rr); + + if (FLAGS_SET(query_flags, SD_RESOLVED_CLAMP_TTL)) { + uint32_t left_ttl; + + assert(current > 0); + + /* Let's determine how much time is left for this cache entry. Note that we round down, but + * clamp this to be 1s at minimum, since we usually want records to remain cached better too + * short a time than too long a time, but otoh don't want to return 0 ever, since that has + * special semantics in various contexts — in particular in mDNS */ + + left_ttl = MAX(1U, LESS_BY(until, current) / USEC_PER_SEC); + + patched = dns_resource_record_ref(rr); + + r = dns_resource_record_clamp_ttl(&patched, left_ttl); + if (r < 0) + return r; + + rr = patched; + + if (rrsig) { + patched_rrsig = dns_resource_record_ref(rrsig); + r = dns_resource_record_clamp_ttl(&patched_rrsig, left_ttl); + if (r < 0) + return r; + + rrsig = patched_rrsig; + } + } + + r = dns_answer_add_extend(answer, rr, ifindex, answer_flags, rrsig); + if (r < 0) + return r; + + return 0; +} + +int dns_cache_lookup( + DnsCache *c, + DnsResourceKey *key, + uint64_t query_flags, + int *ret_rcode, + DnsAnswer **ret_answer, + DnsPacket **ret_full_packet, + uint64_t *ret_query_flags, + DnssecResult *ret_dnssec_result) { + + _cleanup_(dns_packet_unrefp) DnsPacket *full_packet = NULL; + _cleanup_(dns_answer_unrefp) DnsAnswer *answer = NULL; + char key_str[DNS_RESOURCE_KEY_STRING_MAX]; + unsigned n = 0; + int r; + bool nxdomain = false; + DnsCacheItem *first, *nsec = NULL; + bool have_authenticated = false, have_non_authenticated = false, have_confidential = false, have_non_confidential = false; + usec_t current = 0; + int found_rcode = -1; + DnssecResult dnssec_result = -1; + int have_dnssec_result = -1; + + assert(c); + assert(key); + + if (key->type == DNS_TYPE_ANY || key->class == DNS_CLASS_ANY) { + /* If we have ANY lookups we don't use the cache, so that the caller refreshes via the + * network. */ + + log_debug("Ignoring cache for ANY lookup: %s", + dns_resource_key_to_string(key, key_str, sizeof key_str)); + goto miss; + } + + first = dns_cache_get_by_key_follow_cname_dname_nsec(c, key); + if (!first) { + /* If one question cannot be answered we need to refresh */ + + log_debug("Cache miss for %s", + dns_resource_key_to_string(key, key_str, sizeof key_str)); + goto miss; + } + + if (FLAGS_SET(query_flags, SD_RESOLVED_CLAMP_TTL)) { + /* 'current' is always passed to answer_add_clamp_ttl(), but is only used conditionally. + * We'll do the same assert there to make sure that it was initialized properly. */ + current = now(CLOCK_BOOTTIME); + assert(current > 0); + } + + LIST_FOREACH(by_key, j, first) { + /* If the caller doesn't allow us to answer questions from cache data learned from + * "side-effect", skip this entry. */ + if (FLAGS_SET(query_flags, SD_RESOLVED_REQUIRE_PRIMARY) && + !DNS_CACHE_ITEM_IS_PRIMARY(j)) { + log_debug("Primary answer was requested for cache lookup for %s, which we don't have.", + dns_resource_key_to_string(key, key_str, sizeof key_str)); + + goto miss; + } + + if (j->type == DNS_CACHE_NXDOMAIN) + nxdomain = true; + else if (j->type == DNS_CACHE_RCODE) + found_rcode = j->rcode; + else if (j->rr) { + if (j->rr->key->type == DNS_TYPE_NSEC) + nsec = j; + + n++; + } + + if (FLAGS_SET(j->query_flags, SD_RESOLVED_AUTHENTICATED)) + have_authenticated = true; + else + have_non_authenticated = true; + + if (FLAGS_SET(j->query_flags, SD_RESOLVED_CONFIDENTIAL)) + have_confidential = true; + else + have_non_confidential = true; + + if (j->dnssec_result < 0) { + have_dnssec_result = false; /* an entry without dnssec result? then invalidate things for good */ + dnssec_result = _DNSSEC_RESULT_INVALID; + } else if (have_dnssec_result < 0) { + have_dnssec_result = true; /* So far no result seen, let's pick this one up */ + dnssec_result = j->dnssec_result; + } else if (have_dnssec_result > 0 && j->dnssec_result != dnssec_result) { + have_dnssec_result = false; /* conflicting result seen? then invalidate for good */ + dnssec_result = _DNSSEC_RESULT_INVALID; + } + + /* Append the answer RRs to our answer. Ideally we have the answer object, which we + * preferably use. But if the cached entry was generated as "side-effect" of a reply, + * i.e. from validated auxiliary records rather than from the main reply, then we use the + * individual RRs only instead. */ + if (j->answer) { + + /* Minor optimization, if the full answer object of this and the previous RR is the + * same, don't bother adding it again. Typically we store a full RRset here, hence + * that should be the case. */ + if (!j->by_key_prev || j->answer != j->by_key_prev->answer) { + DnsAnswerItem *item; + + DNS_ANSWER_FOREACH_ITEM(item, j->answer) { + r = answer_add_clamp_ttl( + &answer, + item->rr, + item->ifindex, + item->flags, + item->rrsig, + query_flags, + j->until, + current); + if (r < 0) + return r; + } + } + + } else if (j->rr) { + r = answer_add_clamp_ttl( + &answer, + j->rr, + j->ifindex, + FLAGS_SET(j->query_flags, SD_RESOLVED_AUTHENTICATED) ? DNS_ANSWER_AUTHENTICATED : 0, + NULL, + query_flags, + j->until, + current); + if (r < 0) + return r; + } + + /* We'll return any packet we have for this. Typically all cache entries for the same key + * should come from the same packet anyway, hence it doesn't really matter which packet we + * return here, they should all resolve to the same anyway. */ + if (!full_packet && j->full_packet) + full_packet = dns_packet_ref(j->full_packet); + } + + if (found_rcode >= 0) { + log_debug("RCODE %s cache hit for %s", + FORMAT_DNS_RCODE(found_rcode), + dns_resource_key_to_string(key, key_str, sizeof(key_str))); + + if (ret_rcode) + *ret_rcode = found_rcode; + if (ret_answer) + *ret_answer = TAKE_PTR(answer); + if (ret_full_packet) + *ret_full_packet = TAKE_PTR(full_packet); + if (ret_query_flags) + *ret_query_flags = 0; + if (ret_dnssec_result) + *ret_dnssec_result = dnssec_result; + + c->n_hit++; + return 1; + } + + if (nsec && !IN_SET(key->type, DNS_TYPE_NSEC, DNS_TYPE_DS)) { + /* Note that we won't derive information for DS RRs from an NSEC, because we only cache NSEC + * RRs from the lower-zone of a zone cut, but the DS RRs are on the upper zone. */ + + log_debug("NSEC NODATA cache hit for %s", + dns_resource_key_to_string(key, key_str, sizeof key_str)); + + /* We only found an NSEC record that matches our name. If it says the type doesn't exist + * report NODATA. Otherwise report a cache miss. */ + + if (ret_rcode) + *ret_rcode = DNS_RCODE_SUCCESS; + if (ret_answer) + *ret_answer = TAKE_PTR(answer); + if (ret_full_packet) + *ret_full_packet = TAKE_PTR(full_packet); + if (ret_query_flags) + *ret_query_flags = nsec->query_flags; + if (ret_dnssec_result) + *ret_dnssec_result = nsec->dnssec_result; + + if (!bitmap_isset(nsec->rr->nsec.types, key->type) && + !bitmap_isset(nsec->rr->nsec.types, DNS_TYPE_CNAME) && + !bitmap_isset(nsec->rr->nsec.types, DNS_TYPE_DNAME)) { + c->n_hit++; + return 1; + } + + c->n_miss++; + return 0; + } + + log_debug("%s cache hit for %s", + n > 0 ? "Positive" : + nxdomain ? "NXDOMAIN" : "NODATA", + dns_resource_key_to_string(key, key_str, sizeof key_str)); + + if (n <= 0) { + c->n_hit++; + + if (ret_rcode) + *ret_rcode = nxdomain ? DNS_RCODE_NXDOMAIN : DNS_RCODE_SUCCESS; + if (ret_answer) + *ret_answer = TAKE_PTR(answer); + if (ret_full_packet) + *ret_full_packet = TAKE_PTR(full_packet); + if (ret_query_flags) + *ret_query_flags = + ((have_authenticated && !have_non_authenticated) ? SD_RESOLVED_AUTHENTICATED : 0) | + ((have_confidential && !have_non_confidential) ? SD_RESOLVED_CONFIDENTIAL : 0); + if (ret_dnssec_result) + *ret_dnssec_result = dnssec_result; + + return 1; + } + + c->n_hit++; + + if (ret_rcode) + *ret_rcode = DNS_RCODE_SUCCESS; + if (ret_answer) + *ret_answer = TAKE_PTR(answer); + if (ret_full_packet) + *ret_full_packet = TAKE_PTR(full_packet); + if (ret_query_flags) + *ret_query_flags = + ((have_authenticated && !have_non_authenticated) ? SD_RESOLVED_AUTHENTICATED : 0) | + ((have_confidential && !have_non_confidential) ? SD_RESOLVED_CONFIDENTIAL : 0); + if (ret_dnssec_result) + *ret_dnssec_result = dnssec_result; + + return n; + +miss: + if (ret_rcode) + *ret_rcode = DNS_RCODE_SUCCESS; + if (ret_answer) + *ret_answer = NULL; + if (ret_full_packet) + *ret_full_packet = NULL; + if (ret_query_flags) + *ret_query_flags = 0; + if (ret_dnssec_result) + *ret_dnssec_result = _DNSSEC_RESULT_INVALID; + + c->n_miss++; + return 0; +} + +int dns_cache_check_conflicts(DnsCache *cache, DnsResourceRecord *rr, int owner_family, const union in_addr_union *owner_address) { + DnsCacheItem *first; + bool same_owner = true; + + assert(cache); + assert(rr); + + dns_cache_prune(cache); + + /* See if there's a cache entry for the same key. If there + * isn't there's no conflict */ + first = hashmap_get(cache->by_key, rr->key); + if (!first) + return 0; + + /* See if the RR key is owned by the same owner, if so, there + * isn't a conflict either */ + LIST_FOREACH(by_key, i, first) { + if (i->owner_family != owner_family || + !in_addr_equal(owner_family, &i->owner_address, owner_address)) { + same_owner = false; + break; + } + } + if (same_owner) + return 0; + + /* See if there's the exact same RR in the cache. If yes, then + * there's no conflict. */ + if (dns_cache_get(cache, rr)) + return 0; + + /* There's a conflict */ + return 1; +} + +int dns_cache_export_shared_to_packet(DnsCache *cache, DnsPacket *p, usec_t ts, unsigned max_rr) { + unsigned ancount = 0; + DnsCacheItem *i; + int r; + + assert(cache); + assert(p); + assert(p->protocol == DNS_PROTOCOL_MDNS); + + HASHMAP_FOREACH(i, cache->by_key) + LIST_FOREACH(by_key, j, i) { + if (!j->rr) + continue; + + if (!j->shared_owner) + continue; + + /* Ignore cached goodby packet. See on_mdns_packet() and RFC 6762 section 10.1. */ + if (j->rr->ttl <= 1) + continue; + + /* RFC6762 7.1: Don't append records with less than half the TTL remaining + * as known answers. */ + if (usec_sub_unsigned(j->until, ts) < j->rr->ttl * USEC_PER_SEC / 2) + continue; + + if (max_rr > 0 && ancount >= max_rr) { + DNS_PACKET_HEADER(p)->ancount = htobe16(ancount); + ancount = 0; + + r = dns_packet_new_query(&p->more, p->protocol, 0, true); + if (r < 0) + return r; + + p = p->more; + + max_rr = UINT_MAX; + } + + r = dns_packet_append_rr(p, j->rr, 0, NULL, NULL); + if (r == -EMSGSIZE) { + if (max_rr == 0) + /* If max_rr == 0, do not allocate more packets. */ + goto finalize; + + /* If we're unable to stuff all known answers into the given packet, allocate + * a new one, push the RR into that one and link it to the current one. */ + + DNS_PACKET_HEADER(p)->ancount = htobe16(ancount); + ancount = 0; + + r = dns_packet_new_query(&p->more, p->protocol, 0, true); + if (r < 0) + return r; + + /* continue with new packet */ + p = p->more; + r = dns_packet_append_rr(p, j->rr, 0, NULL, NULL); + } + + if (r < 0) + return r; + + ancount++; + } + +finalize: + DNS_PACKET_HEADER(p)->ancount = htobe16(ancount); + + return 0; +} + +void dns_cache_dump(DnsCache *cache, FILE *f) { + DnsCacheItem *i; + + if (!cache) + return; + + if (!f) + f = stdout; + + HASHMAP_FOREACH(i, cache->by_key) + LIST_FOREACH(by_key, j, i) { + + fputc('\t', f); + + if (j->rr) { + const char *t; + t = dns_resource_record_to_string(j->rr); + if (!t) { + log_oom(); + continue; + } + + fputs(t, f); + fputc('\n', f); + } else { + char key_str[DNS_RESOURCE_KEY_STRING_MAX]; + + fputs(dns_resource_key_to_string(j->key, key_str, sizeof key_str), f); + fputs(" -- ", f); + fputs(dns_cache_item_type_to_string(j), f); + fputc('\n', f); + } + } +} + +bool dns_cache_is_empty(DnsCache *cache) { + if (!cache) + return true; + + return hashmap_isempty(cache->by_key); +} + +unsigned dns_cache_size(DnsCache *cache) { + if (!cache) + return 0; + + return hashmap_size(cache->by_key); +} |