From bd4a4eb24ce6f46bec8c5b72312c0cfe2d599fe7 Mon Sep 17 00:00:00 2001 From: Erik Ekman Date: Sun, 20 Sep 2009 15:11:12 +0000 Subject: [PATCH] #75, update dns parsing --- src/dns.c | 184 +++++++++++++++++++++++++++++++++++++++++++++--------- 1 file changed, 154 insertions(+), 30 deletions(-) diff --git a/src/dns.c b/src/dns.c index 075016b..a11e130 100644 --- a/src/dns.c +++ b/src/dns.c @@ -39,6 +39,8 @@ #include "encoding.h" #include "read.h" +#define CHECKLEN(x) if (buflen - (p-buf) < (x)) return 0 + int dns_encode(char *buf, size_t buflen, struct query *q, qr_t qr, char *data, size_t datalen) { @@ -47,6 +49,9 @@ dns_encode(char *buf, size_t buflen, struct query *q, qr_t qr, char *data, size_ char *p; int len; + if (buflen < sizeof(HEADER)) + return 0; + memset(buf, 0, buflen); header = (HEADER*)buf; @@ -68,29 +73,80 @@ dns_encode(char *buf, size_t buflen, struct query *q, qr_t qr, char *data, size_ name = 0xc000 | ((p - buf) & 0x3fff); - putname(&p, sizeof(q->name), q->name); + /* Question section */ + putname(&p, buflen - (p - buf), q->name); + CHECKLEN(4); putshort(&p, q->type); putshort(&p, C_IN); + /* Answer section */ + CHECKLEN(10); putshort(&p, name); - putshort(&p, q->type); + if (q->type == T_A) + putshort(&p, T_CNAME); /* answer CNAME to A question */ + else + putshort(&p, q->type); putshort(&p, C_IN); - putlong(&p, 0); + putlong(&p, 0); /* TTL */ + if (q->type == T_CNAME || q->type == T_A || q->type == T_MX) + { + /* data is expected to be like "Hblabla.host.name.com\0" */ + + char *startp = p; + int namelen; + + p += 2; /* skip 2 bytes length */ + CHECKLEN(2); + if (q->type == T_MX) + putshort(&p, 10); /* preference */ + putname(&p, buflen - (p - buf), data); + CHECKLEN(0); + namelen = p - startp; + namelen -= 2; + putshort(&startp, namelen); + } + else if (q->type == T_TXT) + { + /* TXT has binary or base-X data */ + char *startp = p; + int txtlen; + + p += 2; /* skip 2 bytes length */ + puttxtbin(&p, buflen - (p - buf), data, datalen); + CHECKLEN(0); + txtlen = p - startp; + txtlen -= 2; + putshort(&startp, txtlen); + } + else + { + /* NULL has raw binary data */ + datalen = MIN(datalen, buflen - (p - buf)); + CHECKLEN(2); putshort(&p, datalen); + CHECKLEN(datalen); putdata(&p, data, datalen); + CHECKLEN(0); + } + break; case QR_QUERY: + /* Note that iodined also uses this for forward queries */ + header->qdcount = htons(1); header->arcount = htons(1); - putname(&p, datalen, data); + putname(&p, buflen - (p - buf), data); + CHECKLEN(4); putshort(&p, q->type); putshort(&p, C_IN); - /* EDNS0 */ + /* EDNS0 to advertise maximum response length + (even CNAME/A/MX, 255+255+header would be >512) */ + CHECKLEN(11); putbyte(&p, 0x00); /* Root */ putshort(&p, 0x0029); /* OPT */ putshort(&p, 0x1000); /* Payload size: 4096 */ @@ -107,6 +163,7 @@ dns_encode(char *buf, size_t buflen, struct query *q, qr_t qr, char *data, size_ int dns_encode_ns_response(char *buf, size_t buflen, struct query *q, char *topdomain) +/* Only used when iodined gets an NS type query */ { HEADER *header; int len; @@ -117,6 +174,9 @@ dns_encode_ns_response(char *buf, size_t buflen, struct query *q, char *topdomai int domain_len; char *p; + if (buflen < sizeof(HEADER)) + return 0; + memset(buf, 0, buflen); header = (HEADER*)buf; @@ -148,33 +208,38 @@ dns_encode_ns_response(char *buf, size_t buflen, struct query *q, char *topdomai topname = 0xc000 | ((p - buf + domain_len) & 0x3fff); /* Query section */ - putname(&p, sizeof(q->name), q->name); /* Name */ + putname(&p, buflen - (p - buf), q->name); /* Name */ + CHECKLEN(4); putshort(&p, q->type); /* Type */ putshort(&p, C_IN); /* Class */ /* Answer section */ + CHECKLEN(12); putshort(&p, name); /* Name */ putshort(&p, q->type); /* Type */ putshort(&p, C_IN); /* Class */ - putlong(&p, 0x3ea7d011); /* TTL */ + putlong(&p, 3600); /* TTL */ putshort(&p, 5); /* Data length */ /* pointer to ns.topdomain */ nsname = 0xc000 | ((p - buf) & 0x3fff); + CHECKLEN(5); putbyte(&p, 2); putbyte(&p, 'n'); putbyte(&p, 's'); putshort(&p, topname); /* Name Server */ /* Additional data (A-record of NS server) */ + CHECKLEN(12); putshort(&p, nsname); /* Name Server */ putshort(&p, T_A); /* Type */ putshort(&p, C_IN); /* Class */ - putlong(&p, 0x3ea7d011); /* TTL */ + putlong(&p, 3600); /* TTL */ putshort(&p, 4); /* Data length */ /* ugly hack to output IP address */ domain = (char *) &q->destination; + CHECKLEN(4); putbyte(&p, *domain++); putbyte(&p, *domain++); putbyte(&p, *domain++); @@ -184,6 +249,8 @@ dns_encode_ns_response(char *buf, size_t buflen, struct query *q, char *topdomai return len; } +#undef CHECKLEN + unsigned short dns_get_id(char *packet, size_t packetlen) { @@ -196,6 +263,8 @@ dns_get_id(char *packet, size_t packetlen) return ntohs(header->id); } +#define CHECKLEN(x) if (packetlen - (data-packet) < (x)) return 0 + int dns_decode(char *buf, size_t buflen, struct query *q, qr_t qr, char *packet, size_t packetlen) { @@ -235,27 +304,50 @@ dns_decode(char *buf, size_t buflen, struct query *q, qr_t qr, char *packet, siz switch (qr) { case QR_ANSWER: - if(qdcount != 1 || ancount != 1) { + if(qdcount < 1 || ancount < 1) { + /* We may get both CNAME and A, then ancount=2 */ switch (header->rcode) { - case REFUSED: + case NOERROR: /* 0 */ + if (header->tc) + warnx("Got TRUNCATION as reply: response too long for DNS path"); + else + warnx("Got reply without error, but also without question and/or answer"); + break; + + case FORMERR: /* 1 */ + warnx("Got FORMERR as reply: server does not understand our request"); + break; + + case SERVFAIL: /* 2 */ + if (qdcount >= 1 + && packetlen >= sizeof(HEADER) + 2 + && (data[1] == 'r' || data[1] == 'R')) + warnx("Got SERVFAIL as reply on earlier fragsize autoprobe"); + else if (qdcount >= 1 + && packetlen >= sizeof(HEADER) + 2 + && (data[1] < '0' || data[1] > '9') + && (data[1] < 'a' || data[1] > 'f') + && (data[1] < 'A' || data[1] > 'F') + && data[1] != 'p' && data[1] != 'P') + warnx("Got SERVFAIL as reply on earlier config setting"); + else + warnx("Got SERVFAIL as reply: server failed or recursion timeout"); + break; + + case NXDOMAIN: /* 3 */ + warnx("Got NXDOMAIN as reply: domain does not exist"); + break; + + case NOTIMP: /* 4 */ + warnx("Got NOTIMP as reply: server does not support our request"); + break; + + case REFUSED: /* 5 */ warnx("Got REFUSED as reply"); break; - case NOTIMP: - warnx("Got NOTIMP as reply"); - break; - - case NXDOMAIN: - warnx("Got NXDOMAIN as reply"); - break; - - case SERVFAIL: - warnx("Got SERVFAIL as reply"); - break; - - case NOERROR: default: - warnx("no query or answer in reply packet"); + warnx("Got RCODE %u as reply", (unsigned int) header->rcode); break; } return -1; @@ -265,33 +357,65 @@ dns_decode(char *buf, size_t buflen, struct query *q, qr_t qr, char *packet, siz q->id = id; readname(packet, packetlen, &data, name, sizeof(name)); + CHECKLEN(4); readshort(packet, &data, &type); readshort(packet, &data, &class); + /* Assume that first answer is NULL/CNAME that we wanted */ readname(packet, packetlen, &data, name, sizeof(name)); + CHECKLEN(10); readshort(packet, &data, &type); readshort(packet, &data, &class); readlong(packet, &data, &ttl); readshort(packet, &data, &rlen); - rv = MIN(rlen, sizeof(rdata)); - rv = readdata(packet, &data, rdata, rv); - if(type == T_NULL && rv >= 2 && buf) { - rv = MIN(rv, buflen); - memcpy(buf, rdata, rv); + if (type == T_NULL) { + rv = MIN(rlen, sizeof(rdata)); + rv = readdata(packet, &data, rdata, rv); + if (rv >= 2 && buf) { + rv = MIN(rv, buflen); + memcpy(buf, rdata, rv); + } + /* "else rv=0;" here? */ } + if ((type == T_CNAME || type == T_MX) && buf) { + if (type == T_MX) + data += 2; /* skip preference */ + memset(name, 0, sizeof(name)); + readname(packet, packetlen, &data, name, sizeof(name) - 1); + name[sizeof(name)-1] = '\0'; + strncpy(buf, name, buflen); + buf[buflen - 1] = '\0'; + rv = strlen(buf); + } + if (type == T_TXT && buf) { + rv = readtxtbin(packet, &data, rlen, rdata, sizeof(rdata)); + if (rv >= 1) { + rv = MIN(rv, buflen); + memcpy(buf, rdata, rv); + } + } + if (q != NULL) + q->type = type; break; case QR_QUERY: - if (qdcount != 1) { + if (qdcount < 1) { warnx("no question section in name query"); return -1; } + memset(name, 0, sizeof(name)); readname(packet, packetlen, &data, name, sizeof(name) - 1); name[sizeof(name)-1] = '\0'; + CHECKLEN(4); readshort(packet, &data, &type); readshort(packet, &data, &class); + if (q == NULL) { + rv = 0; + break; + } + strncpy(q->name, name, sizeof(q->name)); q->name[sizeof(q->name) - 1] = '\0'; q->type = type;