442 lines
14 KiB
C
442 lines
14 KiB
C
#include <stdbool.h>
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#include <stdio.h>
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#include <string.h>
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#include <stdlib.h>
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#include <sys/socket.h>
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#include <netinet/in.h>
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#include <stdint.h>
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#include <sys/types.h>
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#include <arpa/inet.h>
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#include <time.h>
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#include <ctype.h>
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#include <unistd.h>
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#include "dns.h"
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#define BUFLEN 512
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#if defined IP_RECVDSTADDR
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# define DSTADDR_SOCKOPT IP_RECVDSTADDR
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# define DSTADDR_DATASIZE (CMSG_SPACE(sizeof(struct in_addr)))
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# define dstaddr(x) (CMSG_DATA(x))
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#elif defined IP_PKTINFO
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struct in_pktinfo {
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unsigned int ipi_ifindex; /* Interface index */
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struct in_addr ipi_spec_dst; /* Local address */
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struct in_addr ipi_addr; /* Header Destination address */
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};
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# define DSTADDR_SOCKOPT IP_PKTINFO
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# define DSTADDR_DATASIZE (CMSG_SPACE(sizeof(struct in_pktinfo)))
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# define dstaddr(x) (&(((struct in_pktinfo *)(CMSG_DATA(x)))->ipi_addr))
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#else
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# error "can't determine socket option"
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#endif
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union control_data {
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struct cmsghdr cmsg;
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unsigned char data[DSTADDR_DATASIZE];
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};
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typedef enum {
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CLASS_IN = 1,
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QCLASS_ANY = 255
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} dns_class;
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typedef enum {
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TYPE_A = 1,
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TYPE_NS = 2,
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TYPE_CNAME = 5,
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TYPE_SOA = 6,
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TYPE_MX = 15,
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TYPE_AAAA = 28,
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TYPE_SRV = 33,
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QTYPE_ANY = 255
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} dns_type;
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// 0: ok
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// -1: premature end of input, forward reference, component > 63 char, invalid character
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// -2: insufficient space in output
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int static parse_name(const unsigned char **inpos, const unsigned char *inend, const unsigned char *inbuf, char *buf, size_t bufsize) {
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size_t bufused = 0;
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int init = 1;
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do {
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if (*inpos == inend)
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return -1;
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// read length of next component
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int octet = *((*inpos)++);
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if (octet == 0) {
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buf[bufused] = 0;
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return 0;
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}
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// add dot in output
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if (!init) {
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if (bufused == bufsize-1)
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return -2;
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buf[bufused++] = '.';
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} else
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init = 0;
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// handle references
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if ((octet & 0xC0) == 0xC0) {
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if (*inpos == inend)
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return -1;
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int ref = ((octet - 0xC0) << 8) + *((*inpos)++);
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if (ref < 0 || ref >= (*inpos)-inbuf) return -1;
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const unsigned char *newbuf = inbuf + ref;
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return parse_name(&newbuf, *inpos, inbuf, buf+bufused, bufsize-bufused);
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}
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if (octet > 63) return -1;
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// copy label
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while (octet) {
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if (*inpos == inend)
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return -1;
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if (bufused == bufsize-1)
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return -2;
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int c = *((*inpos)++);
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if (c == '.')
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return -1;
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octet--;
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buf[bufused++] = c;
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}
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} while(1);
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}
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// 0: k
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// -1: component > 63 characters
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// -2: insufficent space in output
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// -3: two subsequent dots
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int static write_name(unsigned char** outpos, const unsigned char *outend, const char *name, int offset) {
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while (*name != 0) {
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char *dot = strchr(name, '.');
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const char *fin = dot;
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if (!dot) fin = name + strlen(name);
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if (fin - name > 63) return -1;
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if (fin == name) return -3;
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if (outend - *outpos < fin - name + 2) return -2;
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*((*outpos)++) = fin - name;
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memcpy(*outpos, name, fin - name);
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*outpos += fin - name;
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if (!dot) break;
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name = dot + 1;
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}
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if (offset < 0) {
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// no reference
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if (outend == *outpos) return -2;
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*((*outpos)++) = 0;
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} else {
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if (outend - *outpos < 2) return -2;
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*((*outpos)++) = (offset >> 8) | 0xC0;
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*((*outpos)++) = offset & 0xFF;
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}
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return 0;
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}
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int static write_record(unsigned char** outpos, const unsigned char *outend, const char *name, int offset, dns_type typ, dns_class cls, int ttl) {
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unsigned char *oldpos = *outpos;
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int error = 0;
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// name
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int ret = write_name(outpos, outend, name, offset);
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if (ret) { error = ret; goto error; }
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if (outend - *outpos < 8) { error = -4; goto error; }
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// type
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*((*outpos)++) = typ >> 8; *((*outpos)++) = typ & 0xFF;
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// class
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*((*outpos)++) = cls >> 8; *((*outpos)++) = cls & 0xFF;
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// ttl
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*((*outpos)++) = (ttl >> 24) & 0xFF; *((*outpos)++) = (ttl >> 16) & 0xFF; *((*outpos)++) = (ttl >> 8) & 0xFF; *((*outpos)++) = ttl & 0xFF;
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return 0;
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error:
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*outpos = oldpos;
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return error;
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}
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int static write_record_a(unsigned char** outpos, const unsigned char *outend, const char *name, int offset, dns_class cls, int ttl, const addr_t *ip) {
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if (ip->v != 4)
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return -6;
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unsigned char *oldpos = *outpos;
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int error = 0;
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int ret = write_record(outpos, outend, name, offset, TYPE_A, cls, ttl);
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if (ret) return ret;
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if (outend - *outpos < 6) { error = -5; goto error; }
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// rdlength
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*((*outpos)++) = 0; *((*outpos)++) = 4;
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// rdata
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for (int i=0; i<4; i++)
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*((*outpos)++) = ip->data.v4[i];
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return 0;
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error:
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*outpos = oldpos;
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return error;
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}
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int static write_record_aaaa(unsigned char** outpos, const unsigned char *outend, const char *name, int offset, dns_class cls, int ttl, const addr_t *ip) {
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if (ip->v != 6)
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return -6;
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unsigned char *oldpos = *outpos;
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int error = 0;
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int ret = write_record(outpos, outend, name, offset, TYPE_AAAA, cls, ttl);
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if (ret) return ret;
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if (outend - *outpos < 6) { error = -5; goto error; }
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// rdlength
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*((*outpos)++) = 0; *((*outpos)++) = 16;
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// rdata
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for (int i=0; i<16; i++)
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*((*outpos)++) = ip->data.v6[i];
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return 0;
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error:
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*outpos = oldpos;
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return error;
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}
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int static write_record_ns(unsigned char** outpos, const unsigned char *outend, char *name, int offset, dns_class cls, int ttl, const char *ns) {
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unsigned char *oldpos = *outpos;
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int ret = write_record(outpos, outend, name, offset, TYPE_NS, cls, ttl);
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if (ret) return ret;
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int error = 0;
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if (outend - *outpos < 2) { error = -5; goto error; }
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(*outpos) += 2;
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unsigned char *curpos = *outpos;
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ret = write_name(outpos, outend, ns, -1);
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if (ret) { error = ret; goto error; }
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curpos[-2] = (*outpos - curpos) >> 8;
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curpos[-1] = (*outpos - curpos) & 0xFF;
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return 0;
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error:
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*outpos = oldpos;
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return error;
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}
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int static write_record_soa(unsigned char** outpos, const unsigned char *outend, char *name, int offset, dns_class cls, int ttl, const char* mname, const char *rname,
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uint32_t serial, uint32_t refresh, uint32_t retry, uint32_t expire, uint32_t minimum) {
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unsigned char *oldpos = *outpos;
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int ret = write_record(outpos, outend, name, offset, TYPE_SOA, cls, ttl);
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if (ret) return ret;
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int error = 0;
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if (outend - *outpos < 2) { error = -5; goto error; }
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(*outpos) += 2;
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unsigned char *curpos = *outpos;
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ret = write_name(outpos, outend, mname, -1);
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if (ret) { error = ret; goto error; }
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ret = write_name(outpos, outend, rname, -1);
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if (ret) { error = ret; goto error; }
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if (outend - *outpos < 20) { error = -5; goto error; }
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*((*outpos)++) = (serial >> 24) & 0xFF; *((*outpos)++) = (serial >> 16) & 0xFF; *((*outpos)++) = (serial >> 8) & 0xFF; *((*outpos)++) = serial & 0xFF;
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*((*outpos)++) = (refresh >> 24) & 0xFF; *((*outpos)++) = (refresh >> 16) & 0xFF; *((*outpos)++) = (refresh >> 8) & 0xFF; *((*outpos)++) = refresh & 0xFF;
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*((*outpos)++) = (retry >> 24) & 0xFF; *((*outpos)++) = (retry >> 16) & 0xFF; *((*outpos)++) = (retry >> 8) & 0xFF; *((*outpos)++) = retry & 0xFF;
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*((*outpos)++) = (expire >> 24) & 0xFF; *((*outpos)++) = (expire >> 16) & 0xFF; *((*outpos)++) = (expire >> 8) & 0xFF; *((*outpos)++) = expire & 0xFF;
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*((*outpos)++) = (minimum >> 24) & 0xFF; *((*outpos)++) = (minimum >> 16) & 0xFF; *((*outpos)++) = (minimum >> 8) & 0xFF; *((*outpos)++) = minimum & 0xFF;
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curpos[-2] = (*outpos - curpos) >> 8;
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curpos[-1] = (*outpos - curpos) & 0xFF;
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return 0;
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error:
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*outpos = oldpos;
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return error;
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}
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ssize_t static dnshandle(dns_opt_t *opt, const unsigned char *inbuf, size_t insize, unsigned char* outbuf) {
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int error = 0;
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if (insize < 12) // DNS header
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return -1;
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// copy id
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outbuf[0] = inbuf[0];
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outbuf[1] = inbuf[1];
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// copy flags;
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outbuf[2] = inbuf[2];
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outbuf[3] = inbuf[3];
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// clear error
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outbuf[3] &= ~15;
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// check qr
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if (inbuf[2] & 128) { /* printf("Got response?\n"); */ error = 1; goto error; }
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// check opcode
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if (((inbuf[2] & 120) >> 3) != 0) { /* printf("Opcode nonzero?\n"); */ error = 4; goto error; }
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// check Z
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if (((inbuf[3] & 112) >> 4) != 0) { /* printf("Z nonzero?\n"); */ error = 1; goto error; }
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// unset TC
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outbuf[2] &= ~2;
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// unset RA
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outbuf[3] &= ~128;
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// check questions
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int nquestion = (inbuf[4] << 8) + inbuf[5];
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if (nquestion == 0) { /* printf("No questions?\n"); */ error = 0; goto error; }
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if (nquestion > 1) { /* printf("Multiple questions %i?\n", nquestion); */ error = 4; goto error; }
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const unsigned char *inpos = inbuf + 12;
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const unsigned char *inend = inbuf + insize;
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char name[256];
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int offset = inpos - inbuf;
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int ret = parse_name(&inpos, inend, inbuf, name, 256);
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if (ret == -1) { error = 1; goto error; }
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if (ret == -2) { error = 5; goto error; }
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int namel = strlen(name), hostl = strlen(opt->host);
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if (strcmp(name, opt->host) && (namel<hostl+2 || name[namel-hostl-1]!='.' || strcmp(name+namel-hostl,opt->host))) { error = 5; goto error; }
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if (inend - inpos < 4) { error = 1; goto error; }
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// copy question to output
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memcpy(outbuf+12, inbuf+12, inpos+4 - (inbuf+12));
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// set counts
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outbuf[4] = 0; outbuf[5] = 1;
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outbuf[6] = 0; outbuf[7] = 0;
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outbuf[8] = 0; outbuf[9] = 0;
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outbuf[10] = 0; outbuf[11] = 0;
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// set qr
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outbuf[2] |= 128;
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int typ = (inpos[0] << 8) + inpos[1];
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int cls = (inpos[2] << 8) + inpos[3];
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inpos += 4;
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unsigned char *outpos = outbuf+(inpos-inbuf);
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unsigned char *outend = outbuf + BUFLEN;
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// printf("DNS: Request host='%s' type=%i class=%i\n", name, typ, cls);
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// calculate size of authority section
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int auth_size = 0;
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if (!((typ == TYPE_NS || typ == QTYPE_ANY) && (cls == CLASS_IN || cls == QCLASS_ANY))) {
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// authority section will be necessary
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unsigned char *oldpos = outpos;
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write_record_ns(&oldpos, outend, "", offset, CLASS_IN, 0, opt->ns);
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auth_size = oldpos - outpos;
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// printf("Authority section will claim %i bytes\n", auth_size);
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}
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// Answer section
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int have_ns = 0;
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// NS records
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if ((typ == TYPE_NS || typ == QTYPE_ANY) && (cls == CLASS_IN || cls == QCLASS_ANY)) {
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int ret2 = write_record_ns(&outpos, outend - auth_size, "", offset, CLASS_IN, opt->nsttl, opt->ns);
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// printf("wrote NS record: %i\n", ret2);
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if (!ret2) { outbuf[7]++; have_ns++; }
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}
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// SOA records
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if ((typ == TYPE_SOA || typ == QTYPE_ANY) && (cls == CLASS_IN || cls == QCLASS_ANY) && opt->mbox) {
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int ret2 = write_record_soa(&outpos, outend - auth_size, "", offset, CLASS_IN, opt->nsttl, opt->ns, opt->mbox, time(NULL), 604800, 86400, 2592000, 604800);
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// printf("wrote SOA record: %i\n", ret2);
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if (!ret2) { outbuf[7]++; }
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}
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// A/AAAA records
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if ((typ == TYPE_A || typ == TYPE_AAAA || typ == QTYPE_ANY) && (cls == CLASS_IN || cls == QCLASS_ANY)) {
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addr_t addr[32];
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int naddr = opt->cb((void*)opt, addr, 32, typ == TYPE_A || typ == QTYPE_ANY, typ == TYPE_AAAA || typ == QTYPE_ANY);
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int n = 0;
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while (n < naddr) {
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int ret = 1;
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if (addr[n].v == 4)
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ret = write_record_a(&outpos, outend - auth_size, "", offset, CLASS_IN, opt->datattl, &addr[n]);
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else if (addr[n].v == 6)
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ret = write_record_aaaa(&outpos, outend - auth_size, "", offset, CLASS_IN, opt->datattl, &addr[n]);
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// printf("wrote A record: %i\n", ret);
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if (!ret) {
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n++;
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outbuf[7]++;
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} else
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break;
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}
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}
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// Authority section
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if (!have_ns) {
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int ret2 = write_record_ns(&outpos, outend, "", offset, CLASS_IN, opt->nsttl, opt->ns);
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// printf("wrote NS record: %i\n", ret2);
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if (!ret2) {
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outbuf[9]++;
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}
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}
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// set AA
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outbuf[2] |= 4;
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return outpos - outbuf;
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error:
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// set error
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outbuf[3] |= error & 0xF;
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// set counts
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outbuf[4] = 0; outbuf[5] = 0;
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outbuf[6] = 0; outbuf[7] = 0;
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outbuf[8] = 0; outbuf[9] = 0;
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outbuf[10] = 0; outbuf[11] = 0;
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return 12;
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}
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static int listenSocket = -1;
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int dnsserver(dns_opt_t *opt) {
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struct sockaddr_in si_other;
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int senderSocket = -1;
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senderSocket = socket(AF_INET, SOCK_DGRAM, IPPROTO_UDP);
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if (senderSocket == -1)
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return -3;
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int replySocket;
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if (listenSocket == -1) {
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struct sockaddr_in si_me;
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if ((listenSocket=socket(AF_INET, SOCK_DGRAM, IPPROTO_UDP))==-1) {
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listenSocket = -1;
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return -1;
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}
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replySocket = socket(AF_INET, SOCK_DGRAM, IPPROTO_UDP);
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if (replySocket == -1)
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{
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close(listenSocket);
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return -1;
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}
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int sockopt = 1;
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setsockopt(listenSocket, IPPROTO_IP, DSTADDR_SOCKOPT, &sockopt, sizeof sockopt);
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memset((char *) &si_me, 0, sizeof(si_me));
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si_me.sin_family = AF_INET;
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si_me.sin_port = htons(opt->port);
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si_me.sin_addr.s_addr = INADDR_ANY;
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if (bind(listenSocket, (struct sockaddr*)&si_me, sizeof(si_me))==-1)
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return -2;
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}
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unsigned char inbuf[BUFLEN], outbuf[BUFLEN];
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struct iovec iov[1] = {
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{
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.iov_base = inbuf,
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.iov_len = sizeof(inbuf),
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},
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};
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union control_data cmsg;
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struct msghdr msg = {
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.msg_name = &si_other,
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.msg_namelen = sizeof(si_other),
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.msg_iov = iov,
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.msg_iovlen = 1,
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.msg_control = &cmsg,
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.msg_controllen = sizeof(cmsg),
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};
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for (; 1; ++(opt->nRequests))
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{
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ssize_t insize = recvmsg(listenSocket, &msg, 0);
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unsigned char *addr = (unsigned char*)&si_other.sin_addr.s_addr;
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// printf("DNS: Request %llu from %i.%i.%i.%i:%i of %i bytes\n", (unsigned long long)(opt->nRequests), addr[0], addr[1], addr[2], addr[3], ntohs(si_other.sin_port), (int)insize);
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if (insize <= 0)
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continue;
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ssize_t ret = dnshandle(opt, inbuf, insize, outbuf);
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if (ret <= 0)
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continue;
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bool handled = false;
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for (struct cmsghdr*hdr = CMSG_FIRSTHDR(&msg); hdr; hdr = CMSG_NXTHDR(&msg, hdr))
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{
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if (hdr->cmsg_level == IPPROTO_IP && hdr->cmsg_type == DSTADDR_SOCKOPT)
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{
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msg.msg_iov[0].iov_base = outbuf;
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sendmsg(listenSocket, &msg, 0);
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msg.msg_iov[0].iov_base = inbuf;
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handled = true;
|
|
}
|
|
}
|
|
if (!handled)
|
|
sendto(listenSocket, outbuf, ret, 0, (struct sockaddr*)&si_other, sizeof(si_other));
|
|
}
|
|
return 0;
|
|
}
|