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iothdns.c
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iothdns.c
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/*
* iothdns.c: client and server utility functions for dns packets RFC 1035 (and updates)
*
* Copyright 2021-2023 Renzo Davoli - Virtual Square Team
* University of Bologna - Italy
*
* This library is free software; you can redistribute it and/or modify it
* under the terms of the GNU Lesser General Public License as published by
* the Free Software Foundation; either version 2.1 of the License, or (at
* your option) any later version.
*
* You should have received a copy of the GNU Lesser General Public License
* along with this library; if not, see <http://www.gnu.org/licenses/>.
*
*/
#include <stdio.h>
#include <stdint.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <poll.h>
#include <ctype.h>
#include <time.h>
#include <errno.h>
#include <sys/socket.h>
#include <sys/uio.h>
#include <sys/random.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <pthread.h>
#include <iothdns.h>
/* sockaddr_storage wastes memory */
#ifdef WASTE_MEMORY_FOR_SOCKADDR_STORAGE
#define sockaddr_in46 sockaddr_storage
#define sin46_family ss_family
#else
#define sockaddr_in46 sockaddr_in6
#define sin46_family sin6_family
#endif
struct iothdns {
struct ioth *stack;
pthread_mutex_t mutex;
struct sockaddr_in46 sockaddr[IOTHDNS_MAXNS];
char *search;
char *paths[IOTHDNS_PATH_SIZE];
};
static char *iothdns_default_paths[IOTHDNS_PATH_SIZE] = {
IOTHDNS_DEFAULT_HOSTS,
IOTHDNS_DEFAULT_SERVICES
};
/* common function to initialize/update iothdns */
#if 0
#define NSTAG "nameserver"
#define NSTAGLEN (sizeof(NSTAG) - 1)
#define SEARCHTAG "search "
#define SEARCHTAGLEN (sizeof(SEARCHTAG) - 1)
#endif
#define NSTAG "nameserver"
#define SEARCHTAG "search"
static struct iothdns *_iothdns_init_f(struct iothdns *iothdns, struct ioth *stack, FILE *fconfig) {
/* create a new iothdns (init) or clean previous configurations */
if (iothdns == NULL) {
iothdns = calloc(1, sizeof(*iothdns));
if (iothdns) {
iothdns->stack = stack;
pthread_mutex_init(&iothdns->mutex, NULL);
pthread_mutex_lock(&iothdns->mutex);
}
} else {
pthread_mutex_lock(&iothdns->mutex);
for (int nsno = 0; nsno < IOTHDNS_MAXNS; nsno++)
iothdns->sockaddr[nsno].sin46_family = PF_UNSPEC;
if (iothdns->search != NULL) {
free(iothdns->search);
iothdns->search = NULL;
}
}
if (iothdns) {
/* parse the resolv.conf syntax */
char *line = NULL;
size_t linelen = 0;
int nsno = 0;
while (getline(&line, &linelen, fconfig) >= 0) {
char *scan = line;
while (*scan && strchr("\t ", *scan)) scan++; //skip heading spaces
if (strchr("#\n", *scan)) continue; // comments and empty lines
size_t thislinelen = strlen(scan);
char optname[thislinelen];
char value[thislinelen];
if (sscanf (scan, "%[a-zA-Z0-9_] %[^\n]%*c", optname, value) > 0) {
if (strcmp(optname, NSTAG) == 0 && nsno < IOTHDNS_MAXNS) {
uint8_t addr[sizeof(struct in6_addr)];
if (inet_pton(AF_INET6, value, addr) == 1) {
struct sockaddr_in6 *sin6 = (struct sockaddr_in6 *) (&iothdns->sockaddr[nsno++]);
sin6->sin6_family = AF_INET6;
sin6->sin6_port = htons(IOTHDNS_DEFAULT_PORT);
sin6->sin6_addr = *((struct in6_addr *) addr);
}
if (inet_pton(AF_INET, value, addr) == 1) {
struct sockaddr_in *sin = (struct sockaddr_in *) (&iothdns->sockaddr[nsno++]);
sin->sin_family = AF_INET;
sin->sin_port = htons(IOTHDNS_DEFAULT_PORT);
sin->sin_addr = *((struct in_addr *) addr);
}
}
if (strcmp(optname, SEARCHTAG) == 0) {
if (iothdns->search != NULL) {
free(iothdns->search);
iothdns->search = NULL;
}
iothdns->search = strdup(value);
}
}
}
if (line != NULL)
free(line);
pthread_mutex_unlock(&iothdns->mutex);
}
return iothdns;
}
/* helper functions to handle file or string configuration */
static struct iothdns *iothdns_init_update(struct iothdns *iothdns,
struct ioth *stack, char *path_config) {
char *path = (path_config == NULL) ? IOTHDNS_DEFAULT_RESOLV_CONF : path_config;
FILE *f = fopen(path, "r");
if (f) {
struct iothdns *new = _iothdns_init_f(iothdns, stack, f);
fclose(f);
return new;
} else
return NULL;
}
static int is_ip_sequence(const char *config) {
for (; *config; config++) {
if (! (isxdigit(*config) || strchr(".:,", *config)))
return 0;
}
return 1;
}
static struct iothdns *iothdns_init_update_strcfg(struct iothdns *iothdns,
struct ioth *stack, char *config) {
if (config == NULL)
return iothdns_init_update(iothdns, stack, NULL);
else {
char *_config;
size_t _configlen;
if (is_ip_sequence(config)) {
FILE *f = open_memstream(&_config, &_configlen);
if (f) {
char *str, *token, *saveptr;
for (str = config; (token = strtok_r(str, ",", &saveptr)) != NULL; str = NULL)
fprintf(f, "nameserver %s\n", token);
fclose(f);
} else
return NULL;
} else {
_config = config;
_configlen = strlen(config);
}
struct iothdns *new = NULL;
FILE *f = fmemopen(_config, _configlen, "r");
if (f) {
new = _iothdns_init_f(iothdns, stack, f);
fclose(f);
}
if (_config != config)
free(_config);
return new;
}
}
struct iothdns *iothdns_init(struct ioth *stack, char *path_config) {
return iothdns_init_update(NULL, stack, path_config);
}
struct iothdns *iothdns_init_strcfg(struct ioth *stack, char *config) {
return iothdns_init_update_strcfg(NULL, stack, config);
}
int iothdns_update(struct iothdns *iothdns, char *path_config) {
return iothdns_init_update(iothdns, NULL, path_config) == NULL ? -1 : 0;
}
int iothdns_update_strcfg(struct iothdns *iothdns, char *config) {
return iothdns_init_update_strcfg(iothdns, NULL, config) == NULL ? -1 : 0;
}
int iothdns_add_nameserver(struct iothdns *iothdns, int af, void *in46_addr) {
int rv = 0;
int nsno = 0;
pthread_mutex_lock(&iothdns->mutex);
for (int nsno = 0; nsno < IOTHDNS_MAXNS; nsno++)
if (iothdns->sockaddr[nsno].sin46_family == PF_UNSPEC)
break;
if (nsno < IOTHDNS_MAXNS) {
if (af == AF_INET6) {
struct sockaddr_in6 *sin6 = (struct sockaddr_in6 *) (&iothdns->sockaddr[nsno]);
sin6->sin6_family = AF_INET6;
sin6->sin6_port = htons(IOTHDNS_DEFAULT_PORT);
sin6->sin6_addr = *((struct in6_addr *) in46_addr);
} else if (af == AF_INET) {
struct sockaddr_in *sin = (struct sockaddr_in *) (&iothdns->sockaddr[nsno]);
sin->sin_family = AF_INET;
sin->sin_port = htons(IOTHDNS_DEFAULT_PORT);
sin->sin_addr = *((struct in_addr *) in46_addr);
} else {
rv = -1;
errno = EAFNOSUPPORT;
}
} else {
rv = -1;
errno = ENOSPC;
}
pthread_mutex_unlock(&iothdns->mutex);
return rv;
}
void iothdns_setpath(struct iothdns *iothdns, enum iothdns_pathtag pathtag, char *newvalue) {
pthread_mutex_lock(&iothdns->mutex);
if (iothdns->paths[pathtag] != NULL) free(iothdns->paths[pathtag]);
if (newvalue == NULL)
iothdns->paths[pathtag] = NULL;
else
iothdns->paths[pathtag] = strdup(newvalue);
pthread_mutex_unlock(&iothdns->mutex);
}
int iothdns_getpath(struct iothdns *iothdns, enum iothdns_pathtag pathtag, char *buf, size_t size) {
pthread_mutex_lock(&iothdns->mutex);
char *value = iothdns->paths[pathtag];
if (value == NULL) value = iothdns_default_paths[pathtag];
int retvalue = snprintf(buf, size, "%s", value);
pthread_mutex_unlock(&iothdns->mutex);
return retvalue;
}
void iothdns_fini(struct iothdns *iothdns) {
pthread_mutex_lock(&iothdns->mutex);
if (iothdns->search != NULL) free(iothdns->search);
for (int i = 0; i < IOTHDNS_PATH_SIZE; i++) {
if (iothdns->paths[i] != NULL)
free(iothdns->paths[i]);
}
pthread_mutex_unlock(&iothdns->mutex);
free(iothdns);
}
/* dialog function prototype **for clients**
dialog = open socket + connect + send + recv reply (or timeout) + close */
typedef size_t dialog_function_t(struct ioth *stack,
const struct sockaddr_in46 *addr,
void *reqbuf, size_t reqbuflen,
void *repbuf, size_t repbuflen);
/* UDP dialog */
static size_t udp_client_dialog(struct ioth *stack,
const struct sockaddr_in46 *addr,
void *reqbuf, size_t reqbuflen,
void *repbuf, size_t repbuflen) {
int s = ioth_msocket(stack, addr->sin46_family, SOCK_DGRAM, 0);
struct pollfd pfd[] = {{s, POLLIN, 0}};
ioth_connect(s, (struct sockaddr *) addr, sizeof(struct sockaddr_in46));
ioth_write(s, reqbuf, reqbuflen);
if (poll(pfd, 1, IOTHDNS_TIMEOUT_MS) == 0) {
ioth_close(s);
return 0;
}
size_t len = ioth_read(s, repbuf, repbuflen);
ioth_close(s);
return len;
}
/* TCP dialog */
static size_t tcp_get_pkt(int s,
void *repbuf, size_t repbuflen) {
struct pollfd pfd[] = {{s, POLLIN, 0}};
if (poll(pfd, 1, IOTHDNS_TIMEOUT_MS) == 0) {
ioth_close(s);
return 0;
}
uint8_t tcpheader[2];
size_t len = ioth_read(s, tcpheader, sizeof(tcpheader));
if (len < sizeof(tcpheader))
return errno = EBADMSG, -1;
size_t pktlen = tcpheader[0] << 8 | tcpheader[1];
if (pktlen > repbuflen)
return errno = EBADMSG, -1;
struct iovec iov_rdd[] = {{repbuf, pktlen}};
for (;;) {
if (poll(pfd, 1, IOTHDNS_TIMEOUT_MS) == 0)
return 0;
len = ioth_readv(s, iov_rdd, 1);
if (len <= 0)
return errno = EBADMSG, -1;
iov_rdd->iov_base = ((uint8_t *) iov_rdd->iov_base) + len;
iov_rdd->iov_len -= len;
if (iov_rdd->iov_len <= 0)
break;
}
return pktlen;
}
static size_t tcp_client_dialog(struct ioth *stack,
const struct sockaddr_in46 *addr,
void *reqbuf, size_t reqbuflen,
void *repbuf, size_t repbuflen) {
int s = ioth_msocket(stack, addr->sin46_family, SOCK_STREAM, 0);
uint8_t tcpheader[2] = {reqbuflen >> 8, reqbuflen};
struct iovec iov_wr[] = {{tcpheader, sizeof(tcpheader)}, {reqbuf, reqbuflen}};
ioth_connect(s, (struct sockaddr *) addr, sizeof(struct sockaddr_in46));
ioth_writev(s, iov_wr, 2);
size_t len = tcp_get_pkt(s, repbuf, repbuflen);
ioth_close(s);
return len;
}
/* client: lookup helper #2.
try all the ns servers */
static struct iothdns_pkt *__iothdns_lookup(struct iothdns *iothdns,
dialog_function_t *dialog_function,
const char *name, int type,
uint8_t *outbuf, size_t outbuflen) {
uint16_t id = random();
int dnsno;
for (dnsno = 0; dnsno < IOTHDNS_MAXNS; dnsno++) {
if (iothdns->sockaddr[dnsno].sin46_family != 0) {
//printf("%d %d\n", dnsno, iothdns->sockaddr[dnsno].sin46_family);
struct iothdns_header h = {id, IOTHDNS_QUERY | IOTHDNS_RD, name, type, IOTHDNS_CLASS_IN};
struct iothdns_pkt *pkt = iothdns_put_header(&h);
struct iovec pktbuf = iothdns_getbuf(pkt);
size_t len = dialog_function(iothdns->stack,
&iothdns->sockaddr[dnsno],
pktbuf.iov_base, pktbuf.iov_len,
outbuf, outbuflen);
char qname[IOTHDNS_MAXNAME];
iothdns_free(pkt);
pkt = iothdns_get_header(&h, outbuf, len, qname);
if (pkt != NULL && len > 0 && h.id == id && strcmp(h.qname, name) == 0 &&
h.qtype == type && IOTHDNS_IS_RESPONSE(h.flags)) {
switch (IOTHDNS_GET_RCODE(h.flags)) {
case IOTHDNS_RCODE_OK:
return pkt;
case IOTHDNS_RCODE_ENOENT:
free(pkt);
return errno = ENOENT, NULL;
}
}
if (pkt != NULL)
iothdns_free(pkt);
}
}
return NULL;
}
/* client: lookup helper #1.
mutex for concurrent updates.
if the name is just a hostname call the helper #2 trying to complete the fqdn using each item of the
search list.
otherwise call the helper #2 here above */
static struct iothdns_pkt *_iothdns_lookup(struct iothdns *iothdns,
dialog_function_t *dialog_function,
const char *name, int type,
uint8_t *outbuf, size_t outbuflen) {
struct iothdns_pkt *retval;
pthread_mutex_lock(&iothdns->mutex);
if (*name != '\0' && strchr(name, '.') == NULL && iothdns->search != NULL) {
char qname[IOTHDNS_MAXNAME];
retval = NULL;
for (char *scan = iothdns->search;
*scan != '\0' && retval == NULL; scan++) {
if (*scan == ' ') continue;
int len = strchrnul(scan, ' ') - scan;
snprintf(qname, IOTHDNS_MAXNAME, "%s.%.*s",
name, scan[len - 1] == '.' ? len - 1 : len, scan); //delete trailing '.'
// printf("SEARCH! %s\n", qname);
retval = __iothdns_lookup(iothdns, dialog_function, qname, type,
outbuf, outbuflen);
scan += len - 1;
}
} else {
retval = __iothdns_lookup(iothdns, dialog_function, name, type,
outbuf, outbuflen);
}
pthread_mutex_unlock(&iothdns->mutex);
return retval;
}
/* prototype for lookup functions */
typedef struct iothdns_pkt *iothdns_lookup_f_t(struct iothdns *iothdns,
const char *name, int type,
uint8_t *outbuf, size_t outbuflen);
/* lookup via UDP */
static struct iothdns_pkt *iothdns_udp_lookup(struct iothdns *iothdns,
const char *name, int type,
uint8_t *outbuf, size_t outbuflen) {
return _iothdns_lookup(iothdns, udp_client_dialog,
name, type, outbuf, outbuflen);
}
/* lookup via TCP */
static struct iothdns_pkt *iothdns_tcp_lookup(struct iothdns *iothdns,
const char *name, int type,
uint8_t *outbuf, size_t outbuflen) {
return _iothdns_lookup(iothdns, tcp_client_dialog,
name, type, outbuf, outbuflen);
}
/* helper function to support numeric a/aaaa queries via inet_pton */
static int iothdns_lookup_pton(int af, const char *src, void *dst, int n) {
if (n == 0) {
uint8_t tmpbuf[sizeof(struct in6_addr)];
return inet_pton(af, src, tmpbuf);
} else
return inet_pton(af, src, dst);
}
/* lookup IPv4 addresses */
int iothdns_lookup_a(struct iothdns *iothdns, const char *name, struct in_addr *a, int n) {
int retval = iothdns_lookup_pton(AF_INET, name, a, n);
// query the dns only when it is not a numerical address v4 or v6
if (retval == 0 && iothdns_lookup_pton(AF_INET6, name, NULL, 0) == 0) {
uint8_t buf[IOTHDNS_UDP_MAXBUF];
struct iothdns_pkt *pkt = iothdns_udp_lookup(iothdns, name, IOTHDNS_TYPE_A, buf, IOTHDNS_UDP_MAXBUF);
struct iothdns_rr rr;
char rname[IOTHDNS_MAXNAME];
int section;
if (pkt == NULL)
return -1;
while ((section = iothdns_get_rr(pkt, &rr, rname)) != 0) {
if (section == IOTHDNS_SEC_ANSWER && rr.type == IOTHDNS_TYPE_A) {
if (retval < n)
iothdns_get_a(pkt, a + retval);
retval++;
}
}
iothdns_free(pkt);
}
return retval;
}
/* lookup IPv6 addresses */
int iothdns_lookup_aaaa(struct iothdns *iothdns, const char *name, struct in6_addr *aaaa, int n) {
int retval = iothdns_lookup_pton(AF_INET6, name, aaaa, n);
// query the dns only when it is not a numerical address v4 or v6
if (retval == 0 && iothdns_lookup_pton(AF_INET, name, NULL, 0) == 0) {
uint8_t buf[IOTHDNS_UDP_MAXBUF];
struct iothdns_pkt *pkt = iothdns_udp_lookup(iothdns, name, IOTHDNS_TYPE_AAAA, buf, IOTHDNS_UDP_MAXBUF);
struct iothdns_rr rr;
char rname[IOTHDNS_MAXNAME];
int section;
if (pkt == NULL)
return -1;
while ((section = iothdns_get_rr(pkt, &rr, rname)) != 0) {
if (section == IOTHDNS_SEC_ANSWER && rr.type == IOTHDNS_TYPE_AAAA) {
if (retval < n)
iothdns_get_aaaa(pkt, aaaa + retval);
retval++;
}
}
iothdns_free(pkt);
}
return retval;
}
/* lookup IPv6 addresses + IPv4 compat (e.g. ::ffff:1.2.3.4) */
#define v4v6compat(X) \
(struct in6_addr) {.s6_addr32[2] = htonl(0xffff), .s6_addr32[3] = (X).s_addr}
int iothdns_lookup_aaaa_compat(struct iothdns *iothdns, const char *name, struct in6_addr *aaaa, int n) {
int n6 = iothdns_lookup_aaaa(iothdns, name, aaaa, n);
if (n6 < 0)
return n6;
int nmax4 = n - n6;
if (nmax4 > 0) {
struct in_addr a4[nmax4];
int n4 = iothdns_lookup_a(iothdns, name, a4, nmax4);
if (n4 < 0)
return n6;
if (n4 < nmax4) nmax4 = n4;
for (int i = 0; i < nmax4; i++)
aaaa[n6 + i] = v4v6compat(a4[i]);
return n6 + n4;
} else
return n6 + iothdns_lookup_a(iothdns, name, NULL, 0);
}
static int _iothdns_lookup_cb(struct iothdns *iothdns, const char *name, int qtype,
lookup_cb_t *lookup_cb, void *arg,
iothdns_lookup_f_t *iothdns_lookup_f, size_t outbuflen) {
int retval = 0;
uint8_t buf[outbuflen];
struct iothdns_rr rr;
char rname[IOTHDNS_MAXNAME];
int section;
struct iothdns_pkt *pkt = iothdns_lookup_f(iothdns, name, qtype, buf, outbuflen);
if (pkt == NULL)
return -1;
while (retval == 0 && (section = iothdns_get_rr(pkt, &rr, rname)) != 0) {
retval = lookup_cb(section, &rr, pkt, arg);
}
iothdns_free(pkt);
return retval;
}
/* general purpose lookup function: it calls 'lookup_cb' for each resource record */
int iothdns_lookup_cb(struct iothdns *iothdns, const char *name, int qtype,
lookup_cb_t *lookup_cb, void *arg) {
return _iothdns_lookup_cb(iothdns, name, qtype, lookup_cb, arg, iothdns_udp_lookup, IOTHDNS_UDP_MAXBUF);
}
int iothdns_lookup_cb_tcp(struct iothdns *iothdns, const char *name, int qtype,
lookup_cb_t *lookup_cb, void *arg) {
return _iothdns_lookup_cb(iothdns, name, qtype, lookup_cb, arg, iothdns_tcp_lookup, IOTHDNS_TCP_MAXBUF);
}
/* **server side** process a UDP message */
int iothdns_udp_process_request(int fd,
parse_request_t *parse_request, void *arg) {
char buf[IOTHDNS_UDP_MAXBUF];
struct sockaddr_in46 from;
socklen_t fromlen = sizeof(from);
size_t len = ioth_recvfrom(fd, buf, IOTHDNS_UDP_MAXBUF, 0, (struct sockaddr *) &from, &fromlen);
if (len <= 0)
return len;
struct iothdns_header h;
char qname[IOTHDNS_MAXNAME];
struct iothdns_pkt *pkt = iothdns_get_header(&h, buf, len, qname);
iothdns_free(pkt);
if (pkt != NULL && IOTHDNS_IS_QUERY(h.flags)) {
pkt = parse_request(&h, arg);
struct iovec pktbuf = iothdns_getbuf(pkt);
ioth_sendto(fd, pktbuf.iov_base, pktbuf.iov_len, 0, (struct sockaddr *) &from, fromlen);
}
return len;
}
/* **server side** process a TCP message */
int iothdns_tcp_process_request(int fd,
parse_request_t *parse_request, void *arg) {
char buf[IOTHDNS_TCP_MAXBUF];
size_t len = tcp_get_pkt(fd, buf, IOTHDNS_TCP_MAXBUF);
if (len <= 0)
return len;
struct iothdns_header h;
char qname[IOTHDNS_MAXNAME];
struct iothdns_pkt *pkt = iothdns_get_header(&h, buf, len, qname);
iothdns_free(pkt);
if (pkt != NULL && IOTHDNS_IS_QUERY(h.flags)) {
pkt = parse_request(&h, arg);
struct iovec pktbuf = iothdns_getbuf(pkt);
uint8_t tcpheader[2] = {pktbuf.iov_len >> 8, pktbuf.iov_len};
struct iovec iov_wr[] = {{tcpheader, sizeof(tcpheader)}, pktbuf};
ioth_writev(fd, iov_wr, 2);
}
return len;
}
__attribute__((constructor))
static void init(void) {
unsigned int seed;
if (getrandom(&seed, sizeof(seed), 0) == 0)
srand(seed);
else
srand(time(NULL) ^ getpid());
}