ttl(4B) + rlen(2B) + r (MAX_NAME_LEN =21B) +
2*querystring (2 MAX_NAME_LEN= 42B), all together 90 Byte
*/
- MAX_PACK_LEN = 512 + 1,
+ MAX_PACK_LEN = 512,
DEFAULT_TTL = 30, // increase this when not testing?
REQ_PTR = 12
};
-struct dns_repl { // resource record, add 0 or 1 to accepted dns_msg in resp
- uint16_t rlen;
- uint8_t *r; // resource
- uint16_t flags;
-};
-
struct dns_head { // the message from client and first part of response mag
uint16_t id;
uint16_t flags;
return -1;
}
-
/*
* Decode message and generate answer
*/
-static int process_packet(uint8_t * buf)
+static int process_packet(uint8_t *buf)
{
+ uint8_t answstr[MAX_NAME_LEN + 1];
struct dns_head *head;
struct dns_prop *qprop;
- struct dns_repl outr;
- void *next, *from, *answb;
-
- uint8_t answstr[MAX_NAME_LEN + 1];
- int lookup_result, type, len, packet_len;
+ uint8_t *from, *answb;
+ uint16_t outr_rlen;
+ uint16_t outr_flags;
uint16_t flags;
+ int lookup_result, type, packet_len;
+ int querystr_len;
answstr[0] = '\0';
}
from = (void *)&head[1]; // start of query string
- next = answb = from + strlen((char *)from) + 1 + sizeof(struct dns_prop); // where to append answer block
+//FIXME: strlen of untrusted data??!
+ querystr_len = strlen((char *)from) + 1 + sizeof(struct dns_prop);
+ answb = from + querystr_len; // where to append answer block
- outr.rlen = 0; // may change later
- outr.r = NULL;
- outr.flags = 0;
+ outr_rlen = 0;
+ outr_flags = 0;
qprop = (struct dns_prop *)(answb - 4);
type = ntohs(qprop->type);
}
if (ntohs(qprop->class) != 1 /* class INET */ ) {
- outr.flags = 4; /* not supported */
+ outr_flags = 4; /* not supported */
goto empty_packet;
}
/* we only support standard queries */
// We have a standard query
bb_info_msg("%s", (char *)from);
- lookup_result = table_lookup(type, answstr, (uint8_t*)from);
+ lookup_result = table_lookup(type, answstr, from);
if (lookup_result != 0) {
- outr.flags = 3 | 0x0400; //name do not exist and auth
+ outr_flags = 3 | 0x0400; // name do not exist and auth
goto empty_packet;
}
if (type == REQ_A) { // return an address
- struct in_addr a;
- if (!inet_aton((char*)answstr, &a)) {//dotted dec to long conv
- outr.flags = 1; /* Frmt err */
+ struct in_addr a; // NB! its "struct { unsigned __long__ s_addr; }"
+ uint32_t v32;
+ if (!inet_aton((char*)answstr, &a)) { //dotted dec to long conv
+ outr_flags = 1; /* Frmt err */
goto empty_packet;
}
- memcpy(answstr, &a.s_addr, 4); // save before a disappears
- outr.rlen = 4; // uint32_t IP
+ v32 = a.s_addr; /* in case long != int */
+ memcpy(answstr, &v32, 4);
+ outr_rlen = 4; // uint32_t IP
} else
- outr.rlen = strlen((char *)answstr) + 1; // a host name
- outr.r = answstr; // 32 bit ip or a host name
- outr.flags |= 0x0400; /* authority-bit */
+ outr_rlen = strlen((char *)answstr) + 1; // a host name
+ outr_flags |= 0x0400; /* authority-bit */
// we have an answer
head->nansw = htons(1);
// copy query block to answer block
- len = answb - from;
- memcpy(answb, from, len);
- next += len;
+ memcpy(answb, from, querystr_len);
+ answb += querystr_len;
// and append answer rr
- *(uint32_t *) next = htonl(ttl);
- next += 4;
- *(uint16_t *) next = htons(outr.rlen);
- next += 2;
- memcpy(next, (void *)answstr, outr.rlen);
- next += outr.rlen;
+// FIXME: unaligned accesses??
+ *(uint32_t *) answb = htonl(ttl);
+ answb += 4;
+ *(uint16_t *) answb = htons(outr_rlen);
+ answb += 2;
+ memcpy(answb, answstr, outr_rlen);
+ answb += outr_rlen;
empty_packet:
flags = ntohs(head->flags);
// clear rcode and RA, set responsebit and our new flags
- flags |= (outr.flags & 0xff80) | 0x8000;
+ flags |= (outr_flags & 0xff80) | 0x8000;
head->flags = htons(flags);
- head->nauth = head->nadd = htons(0);
+ head->nauth = head->nadd = 0;
head->nquer = htons(1);
- packet_len = (uint8_t *)next - buf;
+ packet_len = answb - buf;
return packet_len;
}
{
const char *listen_interface = "0.0.0.0";
char *sttl, *sport;
- len_and_sockaddr *lsa;
+ len_and_sockaddr *lsa, *from, *to;
+ unsigned lsa_size;
int udps;
uint16_t port = 53;
- uint8_t buf[MAX_PACK_LEN];
+ /* Paranoid sizing: querystring x2 + ttl + outr_rlen + answstr */
+ /* I'd rather see process_packet() fixed instead... */
+ uint8_t buf[MAX_PACK_LEN * 2 + 4 + 2 + (MAX_NAME_LEN+1)];
getopt32(argv, "i:c:t:p:dv", &listen_interface, &fileconf, &sttl, &sport);
//if (option_mask32 & 0x1) // -i
lsa = xdotted2sockaddr(listen_interface, port);
udps = xsocket(lsa->u.sa.sa_family, SOCK_DGRAM, 0);
xbind(udps, &lsa->u.sa, lsa->len);
- /* xlisten(udps, 50); - ?!! DGRAM sockets are never listened on I think? */
+ socket_want_pktinfo(udps); /* needed for recv_from_to to work */
+ lsa_size = LSA_LEN_SIZE + lsa->len;
+ from = xzalloc(lsa_size);
+ to = xzalloc(lsa_size);
+
bb_info_msg("Accepting UDP packets on %s",
xmalloc_sockaddr2dotted(&lsa->u.sa));
while (1) {
int r;
- socklen_t fromlen = lsa->len;
-// FIXME: need to get *DEST* address (to which of our addresses
-// this query was directed), and reply from the same address.
-// Or else we can exhibit usual UDP ugliness:
-// [ip1.multihomed.ip2] <= query to ip1 <= peer
-// [ip1.multihomed.ip2] => reply from ip2 => peer (confused)
-
-// TODO: recv_from_to
-
- r = recvfrom(udps, buf, sizeof(buf), 0, &lsa->u.sa, &fromlen);
- if (OPT_verbose)
- bb_info_msg("Got UDP packet");
- if (r < 12 || r > 512) {
+ /* Try to get *DEST* address (to which of our addresses
+ * this query was directed), and reply from the same address.
+ * Or else we can exhibit usual UDP ugliness:
+ * [ip1.multihomed.ip2] <= query to ip1 <= peer
+ * [ip1.multihomed.ip2] => reply from ip2 => peer (confused) */
+ memcpy(to, lsa, lsa_size);
+ r = recv_from_to(udps, buf, MAX_PACK_LEN + 1, 0, &from->u.sa, &to->u.sa, lsa->len);
+ if (r < 12 || r > MAX_PACK_LEN) {
bb_error_msg("invalid packet size");
continue;
}
+ if (OPT_verbose)
+ bb_info_msg("Got UDP packet");
+ buf[r] = '\0'; /* paranoia */
r = process_packet(buf);
if (r <= 0)
continue;
- sendto(udps, buf, r, 0, &lsa->u.sa, fromlen);
+ send_to_from(udps, buf, r, 0, &to->u.sa, &from->u.sa, lsa->len);
}
return 0;
}
projects / oweals / busybox.git / commitdiff