working DNS

dns.c

@@ -26,32 +26,51 @@ typedef enum {
 } dns_type;
 
 int port = 53;
-char *host = "seedbeta.bitcoin.sipa.be";
+int datattl = 60;
+char *host = "seedtest.bitcoin.sipa.be";
+char *ns = "vps.sipa.be";
 
 //  0: ok
-// -1: premature end of input
+// -1: premature end of input, forward reference, component > 63 char
-// -2: unsufficient space in output
+// -2: insufficient space in output
-int parse_name(const unsigned char **inpos, const unsigned char *inend, char *buf, size_t bufsize) {
+int parse_name(const unsigned char **inpos, const unsigned char *inend, const unsigned char *inbuf, char *buf, size_t bufsize) {
   size_t bufused = 0;
+  int init = 1;
   do {
     if (*inpos == inend)
       return -1;
-    int octet = *(inpos++);
+    // read length of next component
+    int octet = *((*inpos)++);
     if (octet == 0) {
       buf[bufused] = 0;
       return 0;
     }
+    // add dot in output
+    if (!init) {
+      if (bufused == bufsize-1)
+        return -2;
+      buf[bufused++] = '.';
+    } else
+      init = 0;
+    // handle references
+    if ((octet & 0xC0) == 0xC0) {
+      if (*inpos == inend)
+        return -1;
+      int ref = ((octet - 0xC0) << 8) + *((*inpos)++);
+      if (ref < 0 || ref >= (*inpos)-inbuf) return -1;
+      const unsigned char *newbuf = inbuf + ref;
+      return parse_name(&newbuf, *inpos, inbuf, buf+bufused, bufsize-bufused);
+    }
+    if (octet > 63) return -1;
+    // copy data
     while (octet) {
       if (*inpos == inend)
         return -1;
       if (bufused == bufsize-1)
         return -2;
       octet--;
-      buf[bufused++] = *(inpos++);
+      buf[bufused++] = *((*inpos)++);
     }
-    if (bufused == bufsize-1)
-      return -2;
-    buf[bufused++] = '.';
   } while(1);
 }
 
@@ -59,7 +78,7 @@ int parse_name(const unsigned char **inpos, const unsigned char *inend, char *bu
 // -1: component > 63 characters
 // -2: insufficent space in output
 // -3: two subsequent dots
-int write_name(unsigned char** outpos, unsigned char *outend, char *name) {
+int write_name(unsigned char** outpos, unsigned char *outend, char *name, int offset) {
   while (*name != 0) {
     char *dot = strchr(name, '.');
     char *fin = dot;
@@ -67,36 +86,76 @@ int write_name(unsigned char** outpos, unsigned char *outend, char *name) {
     if (fin - name > 63) return -1;
     if (fin == name) return -3;
     if (outend - *outpos < fin - name + 2) return -2;
-    *(outpos++) = fin - name;
+    *((*outpos)++) = fin - name;
     memcpy(*outpos, name, fin - name);
-    outpos += fin - name;
+    *outpos += fin - name;
     if (!dot) break;
     name = dot + 1;
   }
+  if (offset < 0) {
+    // no reference
     if (outend == *outpos) return -2;
-  *(outpos++) = 0;
+    *((*outpos)++) = 0;
+  } else {
+    if (outend - *outpos < 2) return -2;
+    *((*outpos)++) = (offset >> 8) | 0xC0;
+    *((*outpos)++) = offset & 0xFF;
+  }
   return 0;
 }
 
-int write_record_a(unsigned char** outpos, unsigned char *outend, char *name, int cls, int ttl, uint32_t ip) {
+int write_record(unsigned char** outpos, unsigned char *outend, char *name, int offset, int typ, int cls, int ttl) {
   unsigned char *oldpos = *outpos;
+  int error = 0;
   // name
-  if (write_name(outpos, outend, name)) goto error;
+  int ret = write_name(outpos, outend, name, offset);
-  if (outend - *outpos < 14) goto error;
+  if (ret) { error = ret; goto error; }
+  if (outend - *outpos < 8) { error = -4; goto error; }
   // type
-  *(outpos++) = TYPE_A >> 8; *(outpos++) = TYPE_A & 0xFF;
+  *((*outpos)++) = typ >> 8; *((*outpos)++) = typ & 0xFF;
   // class
-  *(outpos++) = cls >> 8; *(outpos++) = cls & 0xFF;
+  *((*outpos)++) = cls >> 8; *((*outpos)++) = cls & 0xFF;
   // ttl
-  *(outpos++) = (ttl >> 24) & 0xFF; *(outpos++) = (ttl >> 16) & 0xFF; *(outpos++) = (ttl >> 8) & 0xFF; *(outpos++) = ttl & 0xFF;
+  *((*outpos)++) = (ttl >> 24) & 0xFF; *((*outpos)++) = (ttl >> 16) & 0xFF; *((*outpos)++) = (ttl >> 8) & 0xFF; *((*outpos)++) = ttl & 0xFF;
+  return 0;
+error:
+  *outpos = oldpos;
+  return error;
+}
+
+
+int write_record_a(unsigned char** outpos, unsigned char *outend, char *name, int offset, int cls, int ttl, uint32_t ip) {
+  unsigned char *oldpos = *outpos;
+  int error = 0;
+  int ret = write_record(outpos, outend, name, offset, TYPE_A, cls, ttl);
+  if (ret) return ret;
+  if (outend - *outpos < 6) { error = -5; goto error; }
   // rdlength
-  *(outpos++) = 0; *(outpos++) = 4;
+  *((*outpos)++) = 0; *((*outpos)++) = 4;
   // rdata
-  *(outpos++) = (ip >> 24) & 0xFF; *(outpos++) = (ip >> 16) & 0xFF; *(outpos++) = (ip >> 8) & 0xFF; *(outpos++) = ttl & 0xFF;
+  *((*outpos)++) = (ip >> 24) & 0xFF; *((*outpos)++) = (ip >> 16) & 0xFF; *((*outpos)++) = (ip >> 8) & 0xFF; *((*outpos)++) = ttl & 0xFF;
   return 0;
 error:
   *outpos = oldpos;
-  return -1;
+  return error;
+}
+
+int write_record_ns(unsigned char** outpos, unsigned char *outend, char *name, int offset, int cls, int ttl, char *ns) {
+  unsigned char *oldpos = *outpos;
+  int ret = write_record(outpos, outend, name, offset, TYPE_NS, cls, ttl);
+  if (ret) return ret;
+  int error = 0;
+  if (outend - *outpos < 2) { error = -5; goto error; }
+  (*outpos) += 2;
+  unsigned char *curpos = *outpos;
+  ret = write_name(outpos, outend, ns, -1);
+  if (ret) { error = ret; goto error; }
+  curpos[-2] = (*outpos - curpos) >> 8;
+  curpos[-1] = (*outpos - curpos) & 0xFF;
+  return 0;
+error:
+  *outpos = oldpos;
+  return error;
 }
 
 ssize_t dnshandle(const unsigned char *inbuf, size_t insize, unsigned char* outbuf) {
@@ -110,28 +169,31 @@ ssize_t dnshandle(const unsigned char *inbuf, size_t insize, unsigned char* outb
   outbuf[2] = inbuf[2];
   outbuf[3] = inbuf[3];
   // clear error
-  outbuf[3] &= ~240;
+  outbuf[3] &= ~15;
   // check qr
-  if (inbuf[2] & 1) { error = 1; goto error; }
+  if (inbuf[2] & 128) { printf("Got response?\n"); error = 1; goto error; }
   // check opcode
-  if (((inbuf[2] & 30) >> 1) != 0) { error = 4; goto error; }
+  if (((inbuf[2] & 120) >> 3) != 0) { printf("Opcode nonzero?\n"); error = 4; goto error; }
   // check Z
-  if (((inbuf[3] & 14) >> 1) != 0) { error = 1; goto error; }
+  if (((inbuf[3] & 112) >> 4) != 0) { printf("Z nonzero?\n"); error = 1; goto error; }
   // unset TC
-  outbuf[2] &= ~64;
+  outbuf[2] &= ~2;
   // unset RA
-  outbuf[3] &= ~1;
+  outbuf[3] &= ~128;
   // check questions
-  int nquestion = inbuf[4] << 8 + inbuf[5];
+  int nquestion = (inbuf[4] << 8) + inbuf[5];
-  if (nquestion == 0) { error = 0; goto error; }
+  if (nquestion == 0) { printf("No questions?\n"); error = 0; goto error; }
-  if (nquestion > 0) { error = 4; goto error; }
+  if (nquestion > 1) { printf("Multiple questions %i?\n", nquestion); error = 4; goto error; }
   const unsigned char *inpos = inbuf + 12;
   const unsigned char *inend = inbuf + insize;
   char name[256];
-  int ret = parse_name(&inpos, inend, name, 256)) 
+  int offset = inpos - inbuf;
+  int ret = parse_name(&inpos, inend, inbuf, name, 256);
+  printf("got request for host='%s'\n", name);
   if (ret == -1) { error = 1; goto error; }
   if (ret == -2) { error = 5; goto error; }
-  if (strcmp(name, host)) { error = 0; goto error; }
+  int namel = strlen(name), hostl = strlen(host);
+  if (strcmp(name, host) && (namel<hostl+2 || name[namel-hostl-1]!='.' || strcmp(name+namel-hostl,host))) { error = 5; goto error; }
   if (inend - inpos < 4) { error = 1; goto error; }
   // copy question to output
   memcpy(outbuf+12, inbuf+12, inpos+4 - (inbuf+12));
@@ -140,26 +202,70 @@ ssize_t dnshandle(const unsigned char *inbuf, size_t insize, unsigned char* outb
   outbuf[6] = 0;  outbuf[7] = 0;
   outbuf[8] = 0;  outbuf[9] = 0;
   outbuf[10] = 0; outbuf[11] = 0;
+  // set qr
+  outbuf[2] |= 128;
   
-  int typ = inpos[0] << 8 + inpos[1];
+  int typ = (inpos[0] << 8) + inpos[1];
-  int cls = inpos[2] << 8 + inpos[3];
+  int cls = (inpos[2] << 8) + inpos[3];
   inpos += 4;
   
   unsigned char *outpos = outbuf+(inpos-inbuf);
   unsigned char *outend = outbuf + BUFLEN;
   
+  printf("type=%i class=%i\n", typ, cls);
+  
+  // calculate size of authority section
+  
+  int auth_size = 0;
+  
+  if (!((typ == TYPE_NS || typ == QTYPE_ANY) && (cls == CLASS_IN || cls == QCLASS_ANY))) {
+    // authority section will be necessary
+    unsigned char *oldpos = outpos;
+    write_record_ns(&oldpos, outend, "", offset, CLASS_IN, 0, ns);
+    auth_size = oldpos - outpos;
+    printf("Authority section will claim %i bytes\n", auth_size);
+  }
+  
+  // Answer section
+
+  int have_ns = 0;
+
+  if ((typ == TYPE_NS || typ == QTYPE_ANY) && (cls == CLASS_IN || cls == QCLASS_ANY)) {
+    int ret2 = write_record_ns(&outpos, outend, "", offset, CLASS_IN, 30583, ns);
+    printf("wrote NS record: %i\n", ret2);
+    if (!ret2) { outbuf[7]++; have_ns++; }
+  }
+  
+  
+  if ((typ == TYPE_A || typ == QTYPE_ANY) && (cls == CLASS_IN || cls == QCLASS_ANY)) {
     uint32_t ip = 0x01101102;
-  while (!write_record_a(&outpos, outend, host, CLASS_IN, 1, ip)) {
+    do {
+      int ret = write_record_a(&outpos, outend - auth_size, "", offset, CLASS_IN, datattl, ip);
+      printf("wrote A record: %i\n", ret);
+      if (!ret) {
         ip += 0x01101102;
-    outbuf[7] ++;
+        outbuf[7]++;
+      } else
+        break;
+    } while(1);
+  }
+  
+  // Authority section
+  if (!have_ns) {
+    int ret2 = write_record_ns(&outpos, outend, "", offset, CLASS_IN, 30583, ns);
+    printf("wrote NS record: %i\n", ret2);
+    if (!ret2) {
+      outbuf[9]++;
+    }
   }
   
   // set AA
-  outbuf[2] |= 32;
+  outbuf[2] |= 4;
+  
   return outpos - outbuf;
 error:
   // set error
-  outbuf[3] |= error << 4;
+  outbuf[3] |= error & 0xF;
   // set counts
   outbuf[4] = 0;  outbuf[5] = 0;
   outbuf[6] = 0;  outbuf[7] = 0;
@@ -170,7 +276,7 @@ error:
 
 int dnsserver(void) {
   struct sockaddr_in si_me, si_other;
-  int s, i, slen=sizeof(si_other);
+  socklen_t s, i, slen=sizeof(si_other);
   unsigned char inbuf[BUFLEN], outbuf[BUFLEN];
   if ((s=socket(AF_INET, SOCK_DGRAM, IPPROTO_UDP))==-1)
     return -1;
@@ -178,14 +284,15 @@ int dnsserver(void) {
   si_me.sin_family = AF_INET;
   si_me.sin_port = htons(port);
   si_me.sin_addr.s_addr = INADDR_ANY;
-  if (bind(s, &si_me, sizeof(si_me))==-1)
+  if (bind(s, (struct sockaddr*)&si_me, sizeof(si_me))==-1)
     return -2;
   do {
-    ssize_t insize = recvfrom(s, inbuf, BUFLEN, 0, &si_other, &slen);
+    ssize_t insize = recvfrom(s, inbuf, BUFLEN, 0, (struct sockaddr*)&si_other, &slen);
+    printf("Got %i-byte request\n", insize);
     if (insize > 0) {
       ssize_t ret = dnshandle(inbuf, insize, outbuf);
       if (ret > 0)
-        sendto(s, outbuf, ret, &si_other, &slen);
+        sendto(s, outbuf, ret, 0, (struct sockaddr*)&si_other, slen);
     }
   } while(1);
   return 0;