resolve: slightly optimize dns_answer_add()
Previously, dns_answer_add() was O(n^2). With this change dns_packet_extract() becomes ~15 times faster for some extremal case. Before: ``` $ time ./fuzz-dns-packet ~/downloads/clusterfuzz-testcase-minimized-fuzz-dns-packet-5631106733047808 /home/watanabe/downloads/clusterfuzz-testcase-minimized-fuzz-dns-packet-5631106733047808... ok real 0m15.453s user 0m15.430s sys 0m0.007s ``` After: ``` $ time ./fuzz-dns-packet ~/downloads/clusterfuzz-testcase-minimized-fuzz-dns-packet-5631106733047808 /home/watanabe/downloads/clusterfuzz-testcase-minimized-fuzz-dns-packet-5631106733047808... ok real 0m0.831s user 0m0.824s sys 0m0.006s ``` Hopefully fixes oss-fuzz#19227. https://bugs.chromium.org/p/oss-fuzz/issues/detail?id=19227
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@ -8,18 +8,53 @@
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#include "resolved-dns-dnssec.h"
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#include "string-util.h"
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static void dns_answer_item_hash_func(const DnsAnswerItem *a, struct siphash *state) {
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assert(a);
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assert(state);
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siphash24_compress(&a->ifindex, sizeof(a->ifindex), state);
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dns_resource_record_hash_func(a->rr, state);
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}
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static int dns_answer_item_compare_func(const DnsAnswerItem *a, const DnsAnswerItem *b) {
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int r;
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assert(a);
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assert(b);
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r = CMP(a->ifindex, b->ifindex);
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if (r != 0)
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return r;
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return dns_resource_record_compare_func(a->rr, b->rr);
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}
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DEFINE_PRIVATE_HASH_OPS(dns_answer_item_hash_ops, DnsAnswerItem, dns_answer_item_hash_func, dns_answer_item_compare_func);
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DnsAnswer *dns_answer_new(size_t n) {
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_cleanup_set_free_ Set *s = NULL;
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DnsAnswer *a;
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if (n > UINT16_MAX) /* We can only place 64K RRs in an answer at max */
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n = UINT16_MAX;
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s = set_new(&dns_answer_item_hash_ops);
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if (!s)
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return NULL;
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/* Higher multipliers give slightly higher efficiency through hash collisions, but the gains
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* quickly drop off after 2. */
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if (set_reserve(s, n * 2) < 0)
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return NULL;
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a = malloc0(offsetof(DnsAnswer, items) + sizeof(DnsAnswerItem) * n);
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if (!a)
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return NULL;
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a->n_ref = 1;
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a->n_allocated = n;
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a->set_items = TAKE_PTR(s);
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return a;
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}
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@ -30,6 +65,8 @@ static void dns_answer_flush(DnsAnswer *a) {
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if (!a)
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return;
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a->set_items = set_free(a->set_items);
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DNS_ANSWER_FOREACH(rr, a)
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dns_resource_record_unref(rr);
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@ -46,6 +83,8 @@ static DnsAnswer *dns_answer_free(DnsAnswer *a) {
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DEFINE_TRIVIAL_REF_UNREF_FUNC(DnsAnswer, dns_answer, dns_answer_free);
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static int dns_answer_add_raw(DnsAnswer *a, DnsResourceRecord *rr, int ifindex, DnsAnswerFlags flags) {
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int r;
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assert(rr);
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if (!a)
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@ -54,12 +93,21 @@ static int dns_answer_add_raw(DnsAnswer *a, DnsResourceRecord *rr, int ifindex,
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if (a->n_rrs >= a->n_allocated)
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return -ENOSPC;
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a->items[a->n_rrs++] = (DnsAnswerItem) {
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.rr = dns_resource_record_ref(rr),
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a->items[a->n_rrs] = (DnsAnswerItem) {
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.rr = rr,
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.ifindex = ifindex,
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.flags = flags,
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};
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r = set_put(a->set_items, &a->items[a->n_rrs]);
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if (r < 0)
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return r;
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if (r == 0)
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return -EEXIST;
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dns_resource_record_ref(rr);
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a->n_rrs++;
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return 1;
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}
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@ -78,8 +126,7 @@ static int dns_answer_add_raw_all(DnsAnswer *a, DnsAnswer *source) {
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}
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int dns_answer_add(DnsAnswer *a, DnsResourceRecord *rr, int ifindex, DnsAnswerFlags flags) {
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size_t i;
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int r;
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DnsAnswerItem tmp, *exist;
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assert(rr);
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@ -88,36 +135,26 @@ int dns_answer_add(DnsAnswer *a, DnsResourceRecord *rr, int ifindex, DnsAnswerFl
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if (a->n_ref > 1)
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return -EBUSY;
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for (i = 0; i < a->n_rrs; i++) {
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if (a->items[i].ifindex != ifindex)
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continue;
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r = dns_resource_key_equal(a->items[i].rr->key, rr->key);
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if (r < 0)
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return r;
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if (r == 0)
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continue;
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tmp = (DnsAnswerItem) {
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.rr = rr,
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.ifindex = ifindex,
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};
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exist = set_get(a->set_items, &tmp);
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if (exist) {
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/* There's already an RR of the same RRset in place! Let's see if the TTLs more or less
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* match. We don't really care if they match precisely, but we do care whether one is 0 and
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* the other is not. See RFC 2181, Section 5.2. */
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if ((rr->ttl == 0) != (a->items[i].rr->ttl == 0))
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if ((rr->ttl == 0) != (exist->rr->ttl == 0))
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return -EINVAL;
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r = dns_resource_record_payload_equal(a->items[i].rr, rr);
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if (r < 0)
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return r;
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if (r == 0)
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continue;
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/* Entry already exists, keep the entry with the higher RR. */
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if (rr->ttl > a->items[i].rr->ttl) {
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dns_resource_record_ref(rr);
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dns_resource_record_unref(a->items[i].rr);
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a->items[i].rr = rr;
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/* Entry already exists, keep the entry with the higher TTL. */
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if (rr->ttl > exist->rr->ttl) {
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dns_resource_record_unref(exist->rr);
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exist->rr = dns_resource_record_ref(rr);
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}
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a->items[i].flags |= flags;
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exist->flags |= flags;
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return 0;
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}
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@ -6,6 +6,7 @@ typedef struct DnsAnswerItem DnsAnswerItem;
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#include "macro.h"
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#include "resolved-dns-rr.h"
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#include "set.h"
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/* A simple array of resource records. We keep track of the
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* originating ifindex for each RR where that makes sense, so that we
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@ -30,6 +31,7 @@ struct DnsAnswerItem {
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struct DnsAnswer {
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unsigned n_ref;
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Set *set_items; /* Used by dns_answer_add() for optimization. */
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size_t n_rrs, n_allocated;
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DnsAnswerItem items[0];
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};
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@ -1479,7 +1479,7 @@ void dns_resource_record_hash_func(const DnsResourceRecord *rr, struct siphash *
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}
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}
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static int dns_resource_record_compare_func(const DnsResourceRecord *x, const DnsResourceRecord *y) {
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int dns_resource_record_compare_func(const DnsResourceRecord *x, const DnsResourceRecord *y) {
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int r;
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r = dns_resource_key_compare_func(x->key, y->key);
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@ -330,6 +330,7 @@ DnsTxtItem *dns_txt_item_copy(DnsTxtItem *i);
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int dns_txt_item_new_empty(DnsTxtItem **ret);
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void dns_resource_record_hash_func(const DnsResourceRecord *i, struct siphash *state);
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int dns_resource_record_compare_func(const DnsResourceRecord *x, const DnsResourceRecord *y);
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extern const struct hash_ops dns_resource_key_hash_ops;
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extern const struct hash_ops dns_resource_record_hash_ops;
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