working DNS
This commit is contained in:
Pieter Wuille
parent
7721f9c1a3
commit
e93ffbf4df
1 changed files with 155 additions and 48 deletions
203
dns.c
203
dns.c
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@ -26,32 +26,51 @@ typedef enum {
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} dns_type;
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int port = 53;
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char *host = "seedbeta.bitcoin.sipa.be";
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int datattl = 60;
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char *host = "seedtest.bitcoin.sipa.be";
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char *ns = "vps.sipa.be";
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// 0: ok
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// -1: premature end of input
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// -2: unsufficient space in output
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int parse_name(const unsigned char **inpos, const unsigned char *inend, char *buf, size_t bufsize) {
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// -1: premature end of input, forward reference, component > 63 char
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// -2: insufficient space in output
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int 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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int octet = *(inpos++);
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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 data
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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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octet--;
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buf[bufused++] = *(inpos++);
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buf[bufused++] = *((*inpos)++);
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}
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if (bufused == bufsize-1)
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return -2;
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buf[bufused++] = '.';
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} while(1);
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}
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@ -59,7 +78,7 @@ int parse_name(const unsigned char **inpos, const unsigned char *inend, char *bu
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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 write_name(unsigned char** outpos, unsigned char *outend, char *name) {
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int write_name(unsigned char** outpos, unsigned char *outend, char *name, int offset) {
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while (*name != 0) {
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char *dot = strchr(name, '.');
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char *fin = dot;
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@ -67,36 +86,76 @@ int write_name(unsigned char** outpos, unsigned char *outend, char *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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*((*outpos)++) = fin - name;
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memcpy(*outpos, name, fin - name);
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outpos += 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 (outend == *outpos) return -2;
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*(outpos++) = 0;
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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 write_record_a(unsigned char** outpos, unsigned char *outend, char *name, int cls, int ttl, uint32_t ip) {
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int write_record(unsigned char** outpos, unsigned char *outend, char *name, int offset, int typ, int 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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if (write_name(outpos, outend, name)) goto error;
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if (outend - *outpos < 14) goto error;
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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++) = TYPE_A >> 8; *(outpos++) = TYPE_A & 0xFF;
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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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*((*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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// rdlength
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*(outpos++) = 0; *(outpos++) = 4;
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// rdata
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*(outpos++) = (ip >> 24) & 0xFF; *(outpos++) = (ip >> 16) & 0xFF; *(outpos++) = (ip >> 8) & 0xFF; *(outpos++) = ttl & 0xFF;
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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 -1;
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return error;
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}
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int write_record_a(unsigned char** outpos, unsigned char *outend, char *name, int offset, int cls, int ttl, uint32_t ip) {
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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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*((*outpos)++) = (ip >> 24) & 0xFF; *((*outpos)++) = (ip >> 16) & 0xFF; *((*outpos)++) = (ip >> 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 write_record_ns(unsigned char** outpos, unsigned char *outend, char *name, int offset, int cls, int ttl, 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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ssize_t dnshandle(const unsigned char *inbuf, size_t insize, unsigned char* outbuf) {
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@ -110,28 +169,31 @@ ssize_t dnshandle(const unsigned char *inbuf, size_t insize, unsigned char* outb
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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] &= ~240;
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outbuf[3] &= ~15;
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// check qr
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if (inbuf[2] & 1) { error = 1; goto error; }
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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] & 30) >> 1) != 0) { error = 4; goto error; }
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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] & 14) >> 1) != 0) { error = 1; goto error; }
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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] &= ~64;
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outbuf[2] &= ~2;
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// unset RA
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outbuf[3] &= ~1;
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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) { error = 0; goto error; }
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if (nquestion > 0) { error = 4; goto error; }
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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 ret = parse_name(&inpos, inend, 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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printf("got request for host='%s'\n", name);
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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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if (strcmp(name, host)) { error = 0; goto error; }
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int namel = strlen(name), hostl = strlen(host);
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if (strcmp(name, host) && (namel<hostl+2 || name[namel-hostl-1]!='.' || strcmp(name+namel-hostl,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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@ -140,26 +202,70 @@ ssize_t dnshandle(const unsigned char *inbuf, size_t insize, unsigned char* outb
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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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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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uint32_t ip = 0x01101102;
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while (!write_record_a(&outpos, outend, host, CLASS_IN, 1, ip)) {
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ip += 0x01101102;
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outbuf[7] ++;
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printf("type=%i class=%i\n", 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, 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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if ((typ == TYPE_NS || typ == QTYPE_ANY) && (cls == CLASS_IN || cls == QCLASS_ANY)) {
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int ret2 = write_record_ns(&outpos, outend, "", offset, CLASS_IN, 30583, 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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if ((typ == TYPE_A || typ == QTYPE_ANY) && (cls == CLASS_IN || cls == QCLASS_ANY)) {
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uint32_t ip = 0x01101102;
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do {
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int ret = write_record_a(&outpos, outend - auth_size, "", offset, CLASS_IN, datattl, ip);
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printf("wrote A record: %i\n", ret);
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if (!ret) {
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ip += 0x01101102;
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outbuf[7]++;
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} else
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break;
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} while(1);
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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, 30583, 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] |= 32;
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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 << 4;
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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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@ -170,7 +276,7 @@ error:
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int dnsserver(void) {
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struct sockaddr_in si_me, si_other;
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int s, i, slen=sizeof(si_other);
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socklen_t s, i, slen=sizeof(si_other);
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unsigned char inbuf[BUFLEN], outbuf[BUFLEN];
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if ((s=socket(AF_INET, SOCK_DGRAM, IPPROTO_UDP))==-1)
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return -1;
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@ -178,14 +284,15 @@ int dnsserver(void) {
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si_me.sin_family = AF_INET;
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si_me.sin_port = htons(port);
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si_me.sin_addr.s_addr = INADDR_ANY;
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if (bind(s, &si_me, sizeof(si_me))==-1)
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if (bind(s, (struct sockaddr*)&si_me, sizeof(si_me))==-1)
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return -2;
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do {
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ssize_t insize = recvfrom(s, inbuf, BUFLEN, 0, &si_other, &slen);
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ssize_t insize = recvfrom(s, inbuf, BUFLEN, 0, (struct sockaddr*)&si_other, &slen);
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printf("Got %i-byte request\n", insize);
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if (insize > 0) {
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ssize_t ret = dnshandle(inbuf, insize, outbuf);
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if (ret > 0)
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sendto(s, outbuf, ret, &si_other, &slen);
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sendto(s, outbuf, ret, 0, (struct sockaddr*)&si_other, slen);
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}
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} while(1);
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return 0;
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