From ca9b8765aea3a7d22d1fd941aaf653f72628556b Mon Sep 17 00:00:00 2001 From: Felix Fietkau Date: Wed, 28 May 2025 21:39:36 +0200 Subject: [PATCH] dns: rework packet API Allow providing multiple questions/answers for different hostnames within a single packet. Also support sending out the same packet on multiple interfaces. Signed-off-by: Felix Fietkau --- dns.c | 193 +++++++++++++++++++++++++++++------------------------- dns.h | 8 ++- service.c | 27 ++++---- 3 files changed, 121 insertions(+), 107 deletions(-) diff --git a/dns.c b/dns.c index 2078d88..ffa61ba 100644 --- a/dns.c +++ b/dns.c @@ -40,8 +40,15 @@ #include "interface.h" static char name_buffer[MAX_NAME_LEN + 1]; -static char dns_buffer[MAX_NAME_LEN]; -static struct blob_buf ans_buf; + +static struct { + struct dns_header h; + unsigned char data[9000 - sizeof(struct dns_header)]; +} __attribute__((packed)) pkt; +static size_t pkt_len; +static struct dns_question *pkt_q[32]; +static unsigned int pkt_n_q; +static unsigned char *dnptrs[255]; const char* dns_type_string(uint16_t type) @@ -67,121 +74,126 @@ dns_type_string(uint16_t type) return "N/A"; } -void -dns_send_question(struct interface *iface, struct sockaddr *to, - const char *question, int type, int multicast) +void dns_packet_init(void) { - static struct dns_header h; - static struct dns_question q; - static struct iovec iov[] = { - { - .iov_base = &h, - .iov_len = sizeof(h), - }, - { - .iov_base = dns_buffer, - }, - { - .iov_base = &q, - .iov_len = sizeof(q), - } - }; - int len; + dnptrs[0] = (unsigned char *)&pkt; + dnptrs[1] = NULL; + pkt_len = 0; + pkt_n_q = 0; + memset(&pkt.h, 0, sizeof(pkt.h)); +} - h.questions = cpu_to_be16(1); - q.class = cpu_to_be16((multicast ? 0 : CLASS_UNICAST) | 1); - q.type = cpu_to_be16(type); +static inline void *dns_packet_tail(size_t len) +{ + if (pkt_len + len > sizeof(pkt.data)) + return NULL; - len = dn_comp(question, (void *) dns_buffer, sizeof(dns_buffer), NULL, NULL); - if (len < 1) - return; + return &pkt.data[pkt_len]; +} - iov[1].iov_len = len; +static int +dns_packet_add_name(const char *name) +{ + void *data; + + data = dns_packet_tail(MAX_NAME_LEN); + if (!data) + return -1; - DBG(1, "Q <- %s %s\n", dns_type_string(type), question); - if (interface_send_packet(iface, to, iov, ARRAY_SIZE(iov)) < 0) - perror("failed to send question"); + return dn_comp(name, data, MAX_NAME_LEN, dnptrs, dnptrs + ARRAY_SIZE(dnptrs) - 1); } +static void *dns_packet_record_add(size_t data_len, const char *name) +{ + void *data; + int len; -struct dns_reply { - int type; - struct dns_answer a; - uint16_t rdlength; - uint8_t *rdata; - char *buffer; -}; + len = dns_packet_add_name(name); + if (len < 1) + return NULL; + + data = dns_packet_tail(len + data_len); + if (!data) + return NULL; -static int dns_answer_cnt; + pkt_len += len + data_len; -void -dns_init_answer(void) + return data + len; +} + +bool dns_packet_question(const char *name, int type) { - dns_answer_cnt = 0; - blob_buf_init(&ans_buf, 0); + struct dns_question *q; + + q = dns_packet_record_add(sizeof(*q), name); + if (!q) + return false; + + pkt.h.questions += cpu_to_be16(1); + pkt_q[pkt_n_q++] = q; + memset(q, 0, sizeof(*q)); + q->class = cpu_to_be16(1); + q->type = cpu_to_be16(type); + DBG(1, "Q <- %s %s\n", dns_type_string(type), name); + + return true; } -void -dns_add_answer(int type, const uint8_t *rdata, uint16_t rdlength, int ttl) +void dns_packet_answer(const char *name, int type, const uint8_t *rdata, uint16_t rdlength, int ttl) { - struct blob_attr *attr; struct dns_answer *a; - attr = blob_new(&ans_buf, 0, sizeof(*a) + rdlength); - a = blob_data(attr); + pkt.h.flags |= cpu_to_be16(0x8400); + + a = dns_packet_record_add(sizeof(*a) + rdlength, name); + memset(a, 0, sizeof(*a)); a->type = cpu_to_be16(type); a->class = cpu_to_be16(1); a->ttl = cpu_to_be32(ttl); a->rdlength = cpu_to_be16(rdlength); memcpy(a + 1, rdata, rdlength); + DBG(1, "A <- %s %s\n", dns_type_string(be16_to_cpu(a->type)), name); - dns_answer_cnt++; + pkt.h.answers += cpu_to_be16(1); } -void -dns_send_answer(struct interface *iface, struct sockaddr *to, const char *answer) +static void dns_question_set_multicast(struct dns_question *q, bool val) { - uint8_t buffer[256]; - struct blob_attr *attr; - struct dns_header h = { 0 }; - struct iovec *iov; - int answer_len, rem; - int n_iov = 0; - - if (!dns_answer_cnt) - return; - - h.answers = cpu_to_be16(dns_answer_cnt); - h.flags = cpu_to_be16(0x8400); - - iov = alloca(sizeof(struct iovec) * ((dns_answer_cnt * 2) + 1)); - - iov[n_iov].iov_base = &h; - iov[n_iov].iov_len = sizeof(struct dns_header); - n_iov++; - - answer_len = dn_comp(answer, buffer, sizeof(buffer), NULL, NULL); - if (answer_len < 1) - return; - - blob_for_each_attr(attr, ans_buf.head, rem) { - struct dns_answer *a = blob_data(attr); + if (val) + q->class &= ~cpu_to_be16(CLASS_UNICAST); + else + q->class |= cpu_to_be16(CLASS_UNICAST); +} - iov[n_iov].iov_base = buffer; - iov[n_iov].iov_len = answer_len; - n_iov++; +void dns_packet_send(struct interface *iface, struct sockaddr *to, bool query, int multicast) +{ + struct iovec iov = { + .iov_base = &pkt, + .iov_len = sizeof(pkt.h) + pkt_len, + }; + size_t i; - iov[n_iov].iov_base = blob_data(attr); - iov[n_iov].iov_len = blob_len(attr); - n_iov++; + if (query) { + if (multicast < 0) + multicast = interface_multicast(iface); - DBG(1, "A <- %s %s\n", dns_type_string(be16_to_cpu(a->type)), answer); + for (i = 0; i < pkt_n_q; i++) + dns_question_set_multicast(pkt_q[i], multicast); } - if (interface_send_packet(iface, to, iov, n_iov) < 0) + if (interface_send_packet(iface, to, &iov, 1) < 0) perror("failed to send answer"); } +void +dns_send_question(struct interface *iface, struct sockaddr *to, + const char *question, int type, int multicast) +{ + dns_packet_init(); + dns_packet_question(question, type); + dns_packet_send(iface, to, true, multicast); +} + void dns_reply_a(struct interface *iface, struct sockaddr *to, int ttl, const char *hostname) { @@ -189,24 +201,27 @@ dns_reply_a(struct interface *iface, struct sockaddr *to, int ttl, const char *h struct sockaddr_in *sa; struct sockaddr_in6 *sa6; + if (!hostname) + hostname = mdns_hostname_local; + getifaddrs(&ifap); - dns_init_answer(); + dns_packet_init(); for (ifa = ifap; ifa; ifa = ifa->ifa_next) { if (strcmp(ifa->ifa_name, iface->name)) continue; if (ifa->ifa_addr->sa_family == AF_INET) { sa = (struct sockaddr_in *) ifa->ifa_addr; - dns_add_answer(TYPE_A, (uint8_t *) &sa->sin_addr, 4, ttl); + dns_packet_answer(hostname, TYPE_A, (uint8_t *) &sa->sin_addr, 4, ttl); } if (ifa->ifa_addr->sa_family == AF_INET6) { sa6 = (struct sockaddr_in6 *) ifa->ifa_addr; - dns_add_answer(TYPE_AAAA, (uint8_t *) &sa6->sin6_addr, 16, ttl); + dns_packet_answer(hostname, TYPE_AAAA, (uint8_t *) &sa6->sin6_addr, 16, ttl); } } - dns_send_answer(iface, to, hostname ? hostname : mdns_hostname_local); - freeifaddrs(ifap); + + dns_packet_send(iface, to, 0, 0); } void diff --git a/dns.h b/dns.h index 39a1a51..d6991e0 100644 --- a/dns.h +++ b/dns.h @@ -73,11 +73,13 @@ struct interface; extern int cfg_proto; extern int cfg_no_subnet; +void dns_packet_init(void); +bool dns_packet_question(const char *name, int type); +void dns_packet_answer(const char *name, int type, const uint8_t *rdata, uint16_t rdlength, int ttl); +void dns_packet_send(struct interface *iface, struct sockaddr *to, bool query, int multicast); + void dns_send_question(struct interface *iface, struct sockaddr *to, const char *question, int type, int multicast); -void dns_init_answer(void); -void dns_add_answer(int type, const uint8_t *rdata, uint16_t rdlength, int ttl); -void dns_send_answer(struct interface *iface, struct sockaddr *to, const char *answer); void dns_reply_a(struct interface *iface, struct sockaddr *to, int ttl, const char *hostname); void dns_reply_a_additional(struct interface *iface, struct sockaddr *to, int ttl); const char* dns_type_string(uint16_t type); diff --git a/service.c b/service.c index 9d3767b..865309f 100644 --- a/service.c +++ b/service.c @@ -78,18 +78,18 @@ service_instance_name(struct service *s) } static void -service_add_ptr(const char *host, int ttl) +service_add_ptr(const char *name, const char *host, int ttl) { int len = dn_comp(host, mdns_buf, sizeof(mdns_buf), NULL, NULL); if (len < 1) return; - dns_add_answer(TYPE_PTR, mdns_buf, len, ttl); + dns_packet_answer(name, TYPE_PTR, mdns_buf, len, ttl); } static void -service_add_srv(struct service *s, int ttl) +service_add_srv(const char *name, struct service *s, int ttl) { struct dns_srv_data *sd = (struct dns_srv_data *) mdns_buf; int len = sizeof(*sd); @@ -99,7 +99,7 @@ service_add_srv(struct service *s, int ttl) return; sd->port = cpu_to_be16(s->port); - dns_add_answer(TYPE_SRV, mdns_buf, len, ttl); + dns_packet_answer(name, TYPE_SRV, mdns_buf, len, ttl); } #define TOUT_LOOKUP 60 @@ -132,15 +132,12 @@ service_reply_single(struct interface *iface, struct sockaddr *to, struct servic s->t = t; - dns_init_answer(); - service_add_ptr(service_instance_name(s), ttl); - dns_send_answer(iface, to, service); - - dns_init_answer(); - service_add_srv(s, ttl); + dns_packet_init(); + service_add_ptr(service, service_instance_name(s), ttl); + service_add_srv(host, s, ttl); if (s->txt && s->txt_len) - dns_add_answer(TYPE_TXT, (uint8_t *) s->txt, s->txt_len, ttl); - dns_send_answer(iface, to, host); + dns_packet_answer(host, TYPE_TXT, (uint8_t *) s->txt, s->txt_len, ttl); + dns_packet_send(iface, to, 0, 0); } void @@ -163,16 +160,16 @@ service_announce_services(struct interface *iface, struct sockaddr *to, int ttl) struct service *s; int count = 0; - dns_init_answer(); + dns_packet_init(); vlist_for_each_element(&announced_services, s, node) { s->t = 0; if (ttl) { - service_add_ptr(s->service, ttl); + service_add_ptr(C_DNS_SD, s->service, ttl); count++; } } if (count) - dns_send_answer(iface, to, C_DNS_SD); + dns_packet_send(iface, to, 0, 0); } void -- 2.30.2