dnsd: properly set _src_ IP:port on outgoing UDP packets
function old new delta send_to_from - 258 +258 dnsd_main 1500 1568 +68 interrupt 17 19 +2 ------------------------------------------------------------------------------ (add/remove: 1/0 grow/shrink: 2/0 up/down: 328/0) Total: 328 bytes text data bss dec hex filename 797101 658 7428 805187 c4943 busybox_old 797429 658 7428 805515 c4a8b busybox_unstripped
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@ -476,10 +476,12 @@ struct hostent *xgethostbyname(const char *name);
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void socket_want_pktinfo(int fd);
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ssize_t send_to_from(int fd, void *buf, size_t len, int flags,
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const struct sockaddr *from, const struct sockaddr *to,
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const struct sockaddr *to,
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const struct sockaddr *from,
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socklen_t tolen);
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ssize_t recv_from_to(int fd, void *buf, size_t len, int flags,
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struct sockaddr *from, struct sockaddr *to,
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struct sockaddr *from,
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struct sockaddr *to,
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socklen_t sa_size);
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char *xstrdup(const char *s);
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@ -25,10 +25,10 @@ socket_want_pktinfo(int fd)
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}
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#ifdef UNUSED
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ssize_t
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send_to_from(int fd, void *buf, size_t len, int flags,
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const struct sockaddr *from, const struct sockaddr *to,
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const struct sockaddr *to,
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const struct sockaddr *from,
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socklen_t tolen)
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{
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#ifndef IP_PKTINFO
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@ -92,7 +92,6 @@ send_to_from(int fd, void *buf, size_t len, int flags,
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return sendmsg(fd, &msg, flags);
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#endif
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}
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#endif /* UNUSED */
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/* NB: this will never set port# in 'to'!
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* _Only_ IP/IPv6 address part of 'to' is _maybe_ modified.
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@ -36,7 +36,7 @@ enum {
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ttl(4B) + rlen(2B) + r (MAX_NAME_LEN =21B) +
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2*querystring (2 MAX_NAME_LEN= 42B), all together 90 Byte
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*/
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MAX_PACK_LEN = 512 + 1,
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MAX_PACK_LEN = 512,
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DEFAULT_TTL = 30, // increase this when not testing?
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@ -44,12 +44,6 @@ enum {
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REQ_PTR = 12
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};
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struct dns_repl { // resource record, add 0 or 1 to accepted dns_msg in resp
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uint16_t rlen;
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uint8_t *r; // resource
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uint16_t flags;
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};
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struct dns_head { // the message from client and first part of response mag
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uint16_t id;
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uint16_t flags;
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@ -218,20 +212,20 @@ static int table_lookup(uint16_t type, uint8_t * as, uint8_t * qs)
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return -1;
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}
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/*
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* Decode message and generate answer
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*/
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static int process_packet(uint8_t * buf)
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static int process_packet(uint8_t *buf)
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{
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uint8_t answstr[MAX_NAME_LEN + 1];
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struct dns_head *head;
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struct dns_prop *qprop;
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struct dns_repl outr;
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void *next, *from, *answb;
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uint8_t answstr[MAX_NAME_LEN + 1];
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int lookup_result, type, len, packet_len;
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uint8_t *from, *answb;
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uint16_t outr_rlen;
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uint16_t outr_flags;
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uint16_t flags;
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int lookup_result, type, packet_len;
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int querystr_len;
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answstr[0] = '\0';
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@ -247,11 +241,12 @@ static int process_packet(uint8_t * buf)
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}
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from = (void *)&head[1]; // start of query string
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next = answb = from + strlen((char *)from) + 1 + sizeof(struct dns_prop); // where to append answer block
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//FIXME: strlen of untrusted data??!
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querystr_len = strlen((char *)from) + 1 + sizeof(struct dns_prop);
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answb = from + querystr_len; // where to append answer block
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outr.rlen = 0; // may change later
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outr.r = NULL;
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outr.flags = 0;
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outr_rlen = 0;
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outr_flags = 0;
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qprop = (struct dns_prop *)(answb - 4);
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type = ntohs(qprop->type);
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@ -262,7 +257,7 @@ static int process_packet(uint8_t * buf)
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}
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if (ntohs(qprop->class) != 1 /* class INET */ ) {
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outr.flags = 4; /* not supported */
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outr_flags = 4; /* not supported */
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goto empty_packet;
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}
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/* we only support standard queries */
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@ -272,49 +267,50 @@ static int process_packet(uint8_t * buf)
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// We have a standard query
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bb_info_msg("%s", (char *)from);
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lookup_result = table_lookup(type, answstr, (uint8_t*)from);
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lookup_result = table_lookup(type, answstr, from);
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if (lookup_result != 0) {
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outr.flags = 3 | 0x0400; //name do not exist and auth
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outr_flags = 3 | 0x0400; // name do not exist and auth
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goto empty_packet;
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}
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if (type == REQ_A) { // return an address
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struct in_addr a;
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if (!inet_aton((char*)answstr, &a)) {//dotted dec to long conv
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outr.flags = 1; /* Frmt err */
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struct in_addr a; // NB! its "struct { unsigned __long__ s_addr; }"
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uint32_t v32;
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if (!inet_aton((char*)answstr, &a)) { //dotted dec to long conv
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outr_flags = 1; /* Frmt err */
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goto empty_packet;
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}
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memcpy(answstr, &a.s_addr, 4); // save before a disappears
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outr.rlen = 4; // uint32_t IP
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v32 = a.s_addr; /* in case long != int */
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memcpy(answstr, &v32, 4);
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outr_rlen = 4; // uint32_t IP
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} else
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outr.rlen = strlen((char *)answstr) + 1; // a host name
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outr.r = answstr; // 32 bit ip or a host name
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outr.flags |= 0x0400; /* authority-bit */
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outr_rlen = strlen((char *)answstr) + 1; // a host name
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outr_flags |= 0x0400; /* authority-bit */
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// we have an answer
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head->nansw = htons(1);
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// copy query block to answer block
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len = answb - from;
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memcpy(answb, from, len);
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next += len;
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memcpy(answb, from, querystr_len);
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answb += querystr_len;
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// and append answer rr
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*(uint32_t *) next = htonl(ttl);
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next += 4;
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*(uint16_t *) next = htons(outr.rlen);
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next += 2;
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memcpy(next, (void *)answstr, outr.rlen);
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next += outr.rlen;
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// FIXME: unaligned accesses??
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*(uint32_t *) answb = htonl(ttl);
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answb += 4;
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*(uint16_t *) answb = htons(outr_rlen);
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answb += 2;
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memcpy(answb, answstr, outr_rlen);
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answb += outr_rlen;
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empty_packet:
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flags = ntohs(head->flags);
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// clear rcode and RA, set responsebit and our new flags
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flags |= (outr.flags & 0xff80) | 0x8000;
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flags |= (outr_flags & 0xff80) | 0x8000;
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head->flags = htons(flags);
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head->nauth = head->nadd = htons(0);
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head->nauth = head->nadd = 0;
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head->nquer = htons(1);
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packet_len = (uint8_t *)next - buf;
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packet_len = answb - buf;
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return packet_len;
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}
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@ -333,10 +329,13 @@ int dnsd_main(int argc ATTRIBUTE_UNUSED, char **argv)
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{
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const char *listen_interface = "0.0.0.0";
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char *sttl, *sport;
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len_and_sockaddr *lsa;
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len_and_sockaddr *lsa, *from, *to;
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unsigned lsa_size;
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int udps;
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uint16_t port = 53;
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uint8_t buf[MAX_PACK_LEN];
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/* Paranoid sizing: querystring x2 + ttl + outr_rlen + answstr */
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/* I'd rather see process_packet() fixed instead... */
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uint8_t buf[MAX_PACK_LEN * 2 + 4 + 2 + (MAX_NAME_LEN+1)];
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getopt32(argv, "i:c:t:p:dv", &listen_interface, &fileconf, &sttl, &sport);
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//if (option_mask32 & 0x1) // -i
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@ -375,32 +374,34 @@ int dnsd_main(int argc ATTRIBUTE_UNUSED, char **argv)
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lsa = xdotted2sockaddr(listen_interface, port);
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udps = xsocket(lsa->u.sa.sa_family, SOCK_DGRAM, 0);
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xbind(udps, &lsa->u.sa, lsa->len);
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/* xlisten(udps, 50); - ?!! DGRAM sockets are never listened on I think? */
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socket_want_pktinfo(udps); /* needed for recv_from_to to work */
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lsa_size = LSA_LEN_SIZE + lsa->len;
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from = xzalloc(lsa_size);
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to = xzalloc(lsa_size);
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bb_info_msg("Accepting UDP packets on %s",
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xmalloc_sockaddr2dotted(&lsa->u.sa));
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while (1) {
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int r;
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socklen_t fromlen = lsa->len;
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// FIXME: need to get *DEST* address (to which of our addresses
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// this query was directed), and reply from the same address.
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// Or else we can exhibit usual UDP ugliness:
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// [ip1.multihomed.ip2] <= query to ip1 <= peer
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// [ip1.multihomed.ip2] => reply from ip2 => peer (confused)
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// TODO: recv_from_to
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r = recvfrom(udps, buf, sizeof(buf), 0, &lsa->u.sa, &fromlen);
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if (OPT_verbose)
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bb_info_msg("Got UDP packet");
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if (r < 12 || r > 512) {
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/* Try to get *DEST* address (to which of our addresses
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* this query was directed), and reply from the same address.
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* Or else we can exhibit usual UDP ugliness:
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* [ip1.multihomed.ip2] <= query to ip1 <= peer
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* [ip1.multihomed.ip2] => reply from ip2 => peer (confused) */
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memcpy(to, lsa, lsa_size);
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r = recv_from_to(udps, buf, MAX_PACK_LEN + 1, 0, &from->u.sa, &to->u.sa, lsa->len);
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if (r < 12 || r > MAX_PACK_LEN) {
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bb_error_msg("invalid packet size");
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continue;
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}
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if (OPT_verbose)
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bb_info_msg("Got UDP packet");
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buf[r] = '\0'; /* paranoia */
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r = process_packet(buf);
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if (r <= 0)
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continue;
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sendto(udps, buf, r, 0, &lsa->u.sa, fromlen);
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send_to_from(udps, buf, r, 0, &to->u.sa, &from->u.sa, lsa->len);
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}
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return 0;
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}
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