ref: 4d69aacea023546a7150d92e147e531c38de822f
dir: /sys/src/cmd/ndb/dnresolve.c/
/*
* domain name resolvers, see rfcs 1035 and 1123
*/
#include <u.h>
#include <libc.h>
#include <ip.h>
#include <bio.h>
#include <ndb.h>
#include "dns.h"
typedef struct Dest Dest;
typedef struct Query Query;
enum
{
Udp, Tcp,
Answerr= -1,
Answnone,
Maxdest= 32, /* maximum destinations for a request message */
/*
* these are the old values; we're trying longer timeouts now
* primarily for the benefit of remote nameservers querying us
* during times of bad connectivity.
*/
Maxtrans= 5, /* maximum transmissions to a server */
Maxretries= 10, /* cname+actual resends: was 32; have pity on user */
};
struct Dest
{
uchar a[IPaddrlen]; /* ip address */
DN *s; /* name server name */
RR *n; /* name server rr */
int nx; /* number of transmissions */
int code; /* response code; used to clear dp->respcode */
};
struct Query {
DN *dp; /* domain */
ushort type; /* and type to look up */
Request *req;
Query *prev; /* previous query */
int depth;
ushort id; /* request id */
RR *nsrp; /* name servers to consult */
};
static RR* dnresolve1(char*, int, int, Request*, int, int);
static int netquery(Query *);
/*
* reading /proc/pid/args yields either "name args" or "name [display args]",
* so return only display args, if any.
*/
static char *
procgetname(void)
{
int fd, n;
char *lp, *rp;
char buf[256];
snprint(buf, sizeof buf, "/proc/%d/args", getpid());
if((fd = open(buf, OREAD|OCEXEC)) < 0)
return strdup("");
*buf = '\0';
n = read(fd, buf, sizeof buf-1);
close(fd);
if (n >= 0)
buf[n] = '\0';
if ((lp = strchr(buf, '[')) == nil ||
(rp = strrchr(buf, ']')) == nil)
return strdup("");
*rp = '\0';
return strdup(lp+1);
}
void
rrfreelistptr(RR **rpp)
{
RR *rp;
if (rpp == nil || *rpp == nil)
return;
rp = *rpp;
*rpp = nil; /* update pointer in memory before freeing list */
rrfreelist(rp);
}
/*
* lookup 'type' info for domain name 'name'. If it doesn't exist, try
* looking it up as a canonical name.
*
* this process can be quite slow if time-outs are set too high when querying
* nameservers that just don't respond to certain query types. in that case,
* there will be multiple udp retries, multiple nameservers will be queried,
* and this will be repeated for a cname query. the whole thing will be
* retried several times until we get an answer or a time-out.
*/
RR*
dnresolve(char *name, int class, int type, Request *req, RR **cn, int depth,
int recurse, int rooted, int *rcode)
{
RR *rp, *nrp, *drp;
DN *dp;
int loops;
char *procname;
char nname[Domlen];
if(rcode)
*rcode = Rok;
if(depth > 12) /* in a recursive loop? */
return nil;
procname = procgetname();
/*
* hack for systems that don't have resolve search
* lists. Just look up the simple name in the database.
*/
if(!rooted && strchr(name, '.') == nil){
rp = nil;
drp = domainlist(class);
for(nrp = drp; rp == nil && nrp != nil; nrp = nrp->next){
snprint(nname, sizeof nname, "%s.%s", name,
nrp->ptr->name);
rp = dnresolve(nname, class, type, req, cn, depth+1,
recurse, rooted, rcode);
rrfreelist(rrremneg(&rp));
}
if(drp != nil)
rrfreelist(drp);
procsetname("%s", procname);
free(procname);
return rp;
}
/*
* try the name directly
*/
rp = dnresolve1(name, class, type, req, depth, recurse);
if(rp == nil && (dp = idnlookup(name, class, 0)) != nil) {
/*
* try it as a canonical name if we weren't told
* that the name didn't exist
*/
if(type != Tptr && dp->respcode != Rname)
for(loops = 0; rp == nil && loops < Maxretries; loops++){
/* retry cname, then the actual type */
rp = dnresolve1(name, class, Tcname, req,
depth, recurse);
if(rp == nil)
break;
/* rp->host == nil shouldn't happen, but does */
if(rp->negative || rp->host == nil){
rrfreelist(rp);
rp = nil;
break;
}
name = rp->host->name;
if(cn)
rrcat(cn, rp);
else
rrfreelist(rp);
rp = dnresolve1(name, class, type, req,
depth, recurse);
}
/* distinction between not found and not good */
if(rp == nil && rcode != nil && dp->respcode != Rok)
*rcode = dp->respcode;
}
procsetname("%s", procname);
free(procname);
return randomize(rp);
}
static void
initquery(Query *qp, DN *dp, int type, Request *req, int depth)
{
assert(dp != nil);
memset(qp, 0, sizeof *qp);
qp->dp = dp;
qp->type = type;
qp->nsrp = nil;
qp->depth = depth;
qp->prev = req->aux;
qp->req = req;
req->aux = qp;
}
static void
exitquery(Query *qp)
{
if(qp->req->aux == qp)
qp->req->aux = qp->prev;
memset(qp, 0, sizeof *qp); /* prevent accidents */
}
/*
* if the response to a query hasn't arrived within 100 ms.,
* it's unlikely to arrive at all. after 1 s., it's really unlikely.
* queries for missing RRs are likely to produce time-outs rather than
* negative responses, so cname and aaaa queries are likely to time out,
* thus we don't wait very long for them.
*/
static void
notestats(long ms, int tmout, int type)
{
if (tmout) {
stats.tmout++;
if (type == Taaaa)
stats.tmoutv6++;
else if (type == Tcname)
stats.tmoutcname++;
} else {
long wait10ths = ms / 100;
if (wait10ths <= 0)
stats.under10ths[0]++;
else if (wait10ths >= nelem(stats.under10ths))
stats.under10ths[nelem(stats.under10ths) - 1]++;
else
stats.under10ths[wait10ths]++;
}
}
static void
noteinmem(void)
{
stats.answinmem++;
}
/* netquery with given name servers, free ns rrs when done */
static int
netqueryns(Query *qp, RR *nsrp)
{
int rv;
if(nsrp == nil)
return Answnone;
qp->nsrp = nsrp;
rv = netquery(qp);
qp->nsrp = nil; /* prevent accidents */
rrfreelist(nsrp);
return rv;
}
static RR*
issuequery(Query *qp, char *name, int class, int recurse)
{
char *cp;
DN *nsdp;
RR *rp, *nsrp, *dbnsrp;
/*
* if we're running as just a resolver, query our
* designated name servers
*/
if(cfg.resolver){
nsrp = randomize(getdnsservers(class));
if(nsrp != nil)
if(netqueryns(qp, nsrp) > Answnone)
return rrlookup(qp->dp, qp->type, OKneg);
}
/*
* walk up the domain name looking for
* a name server for the domain.
*/
for(cp = name; cp; cp = walkup(cp)){
/*
* if this is a local (served by us) domain,
* return answer
*/
dbnsrp = randomize(dblookup(cp, class, Tns, 0, 0));
if(dbnsrp && dbnsrp->local){
rp = dblookup(name, class, qp->type, 1, dbnsrp->ttl);
rrfreelist(dbnsrp);
return rp;
}
/*
* if recursion isn't set, just accept local
* entries
*/
if(recurse == Dontrecurse){
if(dbnsrp)
rrfreelist(dbnsrp);
continue;
}
/* look for ns in cache */
nsdp = idnlookup(cp, class, 0);
nsrp = nil;
if(nsdp)
nsrp = randomize(rrlookup(nsdp, Tns, NOneg));
/* if the entry timed out, ignore it */
if(nsrp && !nsrp->db && (long)(nsrp->expire - now) <= 0)
rrfreelistptr(&nsrp);
if(nsrp){
rrfreelistptr(&dbnsrp);
/* hack: stop search if ns is authoritative in db */
if(cfg.cachedb && nsrp->db && nsrp->auth)
cp = "";
/* query the name servers found in cache */
if(netqueryns(qp, nsrp) > Answnone)
return rrlookup(qp->dp, qp->type, OKneg);
} else if(dbnsrp)
/* try the name servers found in db */
if(netqueryns(qp, dbnsrp) > Answnone)
return rrlookup(qp->dp, qp->type, NOneg);
}
return nil;
}
static RR*
dnresolve1(char *name, int class, int type, Request *req, int depth, int recurse)
{
Area *area;
DN *dp;
RR *rp;
Query q;
if(debug)
dnslog("%d: dnresolve1 %s %d %d",
req->id, name, type, class);
/* only class Cin implemented so far */
if(class != Cin)
return nil;
dp = idnlookup(name, class, 1);
/*
* Try the cache first
*/
rp = rrlookup(dp, type, OKneg);
if(rp)
if(rp->db){
/* unauthoritative db entries are hints */
if(rp->auth) {
noteinmem();
if(debug)
dnslog("%d: dnresolve1 %s %d %d: auth rr in db",
req->id, name, type, class);
return rp;
}
} else
/* cached entry must still be valid */
if((long)(rp->expire - now) > 0)
/* but Tall entries are special */
if(type != Tall || rp->query == Tall) {
noteinmem();
if(debug)
dnslog("%d: dnresolve1 %s %d %d: rr not in db",
req->id, name, type, class);
return rp;
}
rrfreelist(rp);
rp = nil; /* accident prevention */
USED(rp);
/*
* try the cache for a canonical name. if found punt
* since we'll find it during the canonical name search
* in dnresolve().
*/
if(type != Tcname){
rp = rrlookup(dp, Tcname, NOneg);
rrfreelist(rp);
if(rp){
if(debug)
dnslog("%d: dnresolve1 %s %d %d: rr from rrlookup for non-cname",
req->id, name, type, class);
return nil;
}
}
/*
* if the domain name is within an area of ours,
* we should have found its data in memory by now.
*/
area = inmyarea(dp->name);
if (area || strncmp(dp->name, "local#", 6) == 0)
return nil;
initquery(&q, dp, type, req, depth);
rp = issuequery(&q, name, class, recurse);
exitquery(&q);
if(rp){
if(debug)
dnslog("%d: dnresolve1 %s %d %d: rr from query",
req->id, name, type, class);
return rp;
}
/* settle for a non-authoritative answer */
rp = rrlookup(dp, type, OKneg);
if(rp){
if(debug)
dnslog("%d: dnresolve1 %s %d %d: rr from rrlookup",
req->id, name, type, class);
return rp;
}
/* noone answered. try the database, we might have a chance. */
rp = dblookup(name, class, type, 0, 0);
if (rp) {
if(debug)
dnslog("%d: dnresolve1 %s %d %d: rr from dblookup",
req->id, name, type, class);
}else{
if(debug)
dnslog("%d: dnresolve1 %s %d %d: no rr from dblookup; crapped out",
req->id, name, type, class);
}
return rp;
}
/*
* walk a domain name one element to the right.
* return a pointer to that element.
* in other words, return a pointer to the parent domain name.
*/
char*
walkup(char *name)
{
char *cp;
cp = strchr(name, '.');
if(cp)
return cp+1;
else if(*name)
return "";
else
return 0;
}
/*
* Get a udp port for sending requests and reading replies.
* Put the port into "headers" mode.
*/
int
udpport(char *mntpt)
{
static char hmsg[] = "headers";
static char imsg[] = "ignoreadvice";
char adir[NETPATHLEN], buf[NETPATHLEN];
int fd, ctl;
/* get a udp port */
snprint(buf, sizeof buf, "%s/udp!*!0", mntpt);
ctl = announce(buf, adir);
if(ctl < 0)
return -1;
/* turn on header style interface */
if(write(ctl, hmsg, sizeof(hmsg)-1) < 0){
warning("can't enable %s on %s: %r", hmsg, adir);
close(ctl);
return -1;
}
/* ignore ICMP advice */
write(ctl, imsg, sizeof(imsg)-1);
/* grab the data file */
snprint(buf, sizeof buf, "%s/data", adir);
fd = open(buf, ORDWR|OCEXEC);
if(fd < 0)
warning("can't open udp port %s: %r", buf);
close(ctl);
return fd;
}
static void
initdnsmsg(DNSmsg *mp, RR *rp, int flags, ushort reqno)
{
memset(mp, 0, sizeof *mp);
mp->flags = flags;
mp->id = reqno;
mp->qd = rp;
if(rp != nil)
mp->qdcount = 1;
}
RR*
getednsopt(DNSmsg *mp, int *rcode)
{
RR *rp, *x;
rp = rrremtype(&mp->ar, Topt);
if(rp == nil)
return nil;
mp->arcount--;
while((x = rp->next) != nil){
rp->next = x->next;
rrfree(x);
mp->arcount--;
*rcode = Rformat;
}
if(rp->eflags & Evers)
*rcode = Rbadvers;
if(rp->udpsize < 512)
rp->udpsize = 512;
return rp;
}
int
getercode(DNSmsg *mp)
{
if(mp->edns == nil)
return mp->flags & Rmask;
return (mp->flags & 0xF) | (mp->edns->eflags & Ercode) >> 20;
}
void
setercode(DNSmsg *mp, int rcode)
{
if(mp->edns){
mp->edns->eflags = (mp->edns->eflags & ~Ercode) | ((rcode << 20) & Ercode);
rcode &= 0xF;
}
mp->flags = (mp->flags & ~Rmask) | (rcode & Rmask);
}
RR*
mkednsopt(void)
{
RR *rp;
rp = rralloc(Topt);
rp->owner = dnlookup("", Cin, 1);
rp->eflags = 0;
/*
* Advertise a safe UDP response size
* instead of Maxudp as that is just
* the worst case we can accept.
*
* 1232 = MTU(1280)-IPv6(40)-UDP(8).
*/
rp->udpsize = 1232;
return rp;
}
/* generate a DNS UDP query packet, return size of request (without Udphdr) */
int
mkreq(DN *dp, int type, uchar *pkt, int flags, ushort id)
{
Udphdr *uh = (Udphdr*)pkt;
DNSmsg m;
RR *rp;
int len;
/* stuff port number into output buffer */
memset(uh, 0, Udphdrsize);
uh->rport[1] = 53;
/* make request and convert it to output format */
rp = rralloc(type);
rp->owner = dp;
initdnsmsg(&m, rp, flags, id);
m.edns = mkednsopt();
len = convDNS2M(&m, &pkt[Udphdrsize], Maxudp);
rrfreelist(m.edns);
rrfreelist(rp);
return len;
}
void
freeanswers(DNSmsg *mp)
{
rrfreelistptr(&mp->qd);
rrfreelistptr(&mp->an);
rrfreelistptr(&mp->ns);
rrfreelistptr(&mp->ar);
mp->qdcount = mp->ancount = mp->nscount = mp->arcount = 0;
}
/* timed read of reply. sets srcip if UDP. */
static int
readnet(Query *qp, int medium, int fd, uchar pkt[Maxpkt], uvlong endms,
uchar **replyp, uchar *srcip)
{
int len;
long ms;
uvlong startms;
uchar *reply;
*replyp = nil;
startms = nowms;
ms = (long)(endms - startms);
if (ms < 1)
return -1; /* taking too long */
len = -1; /* pessimism */
reply = pkt;
switch (medium) {
case Udp:
alarm(ms);
len = read(fd, pkt, Udphdrsize + Maxudp);
alarm(0);
if(len < 0)
break;
if(len <= Udphdrsize){
len = -1;
break;
}
ipmove(srcip, pkt);
len -= Udphdrsize;
reply += Udphdrsize;
break;
case Tcp:
alarm(ms);
len = readn(fd, pkt, 2);
if(len < 0){
alarm(0);
break;
}
if(len != 2){
alarm(0);
dnslog("%d: readnet: short read of 2-byte tcp msg size from %I",
qp->req->id, srcip);
len = -1;
break;
}
len = pkt[0]<<8 | pkt[1];
if(len <= 0 || len > Maxtcp || readn(fd, pkt+2, len) != len){
alarm(0);
dnslog("%d: readnet: short read of tcp data from %I",
qp->req->id, srcip);
len = -1;
break;
}
alarm(0);
reply += 2;
break;
}
/* file statistics */
ms = (long)(timems() - startms);
notestats(ms, len < 0, qp->type);
*replyp = reply;
return len;
}
/*
* read replies to a request and remember the rrs in the answer(s).
* ignore any of the wrong type for UDP.
* wait at most until endms.
*/
static int
readreply(Query *qp, int medium, int fd, uvlong endms,
DNSmsg *mp, uchar *srcip)
{
uchar pkt[Maxpkt];
uchar *reply;
char *err;
int len;
RR *rp;
for(;;){
len = readnet(qp, medium, fd, pkt, endms, &reply, srcip);
if (len < 0)
break;
/* convert into internal format */
memset(mp, 0, sizeof *mp);
err = convM2DNS(reply, len, mp, nil);
if (mp->flags & Ftrunc) {
free(err);
return 1; /* signal truncation */
}
if(err){
dnslog("%d: readreply: input err, len %d: %s from %I",
qp->req->id, len, err, srcip);
free(err);
} else {
logreply(qp->req->id, "rcvd", srcip, mp);
/* answering the right question? */
if(mp->id != qp->id)
dnslog("%d: id %d instead of %d from %I",
qp->req->id, mp->id, qp->id, srcip);
else if(mp->qd == 0)
dnslog("%d: no question RR from %I", qp->req->id, srcip);
else if(mp->qd->owner != qp->dp)
dnslog("%d: owner %s instead of %s from %I", qp->req->id,
mp->qd->owner->name, qp->dp->name, srcip);
else if(mp->qd->type != qp->type)
dnslog("%d: qp->type %d instead of %d from %I",
qp->req->id, mp->qd->type, qp->type, srcip);
else {
/* remember what request this is in answer to */
for(rp = mp->an; rp; rp = rp->next)
rp->query = qp->type;
return 0;
}
}
freeanswers(mp);
/* only single reply is expected from TCP */
if(medium == Tcp)
break;
}
memset(mp, 0, sizeof *mp);
return -1;
}
/*
* return non-0 if first list includes second list
*/
int
contains(RR *rp1, RR *rp2)
{
RR *trp1, *trp2;
for(trp2 = rp2; trp2; trp2 = trp2->next){
for(trp1 = rp1; trp1; trp1 = trp1->next)
if(trp1->type == trp2->type)
if(trp1->host == trp2->host)
if(trp1->owner == trp2->owner)
break;
if(trp1 == nil)
return 0;
}
return 1;
}
/*
* return multicast version if any
*/
int
ipisbm(uchar *ip)
{
if(isv4(ip)){
if (ip[IPv4off] >= 0xe0 && ip[IPv4off] < 0xf0 ||
ipcmp(ip, IPv4bcast) == 0)
return 4;
} else
if(ip[0] == 0xff)
return 6;
return 0;
}
static int
queryloops(Query *qp, RR *rp)
{
DN *ns = rp->host;
/*
* looking up a server under itself
*/
if(subsume(rp->owner->name, ns->name))
return 1;
/*
* cycle on name servers refering
* to each another.
*/
for(; qp; qp = qp->prev)
if(qp->dp == ns)
return 1;
return 0;
}
/*
* Get next server type address(es) into dest[nd] and beyond
*/
static int
serveraddrs(Query *qp, Dest dest[Maxdest], int nd, int type)
{
RR *rp, *arp, *trp;
ulong mark;
Dest *p;
if(nd >= Maxdest) /* dest array is full? */
return Maxdest;
/*
* look for a server whose address we already know.
* if we find one, mark it so we ignore this on
* subsequent passes.
*/
mark = 1UL<<type;
arp = nil;
for(rp = qp->nsrp; rp; rp = rp->next){
if(rp->marker & mark)
continue;
arp = rrlookup(rp->host, type, NOneg);
if(arp){
rp->marker |= mark;
break;
}
arp = dblookup(rp->host->name, Cin, type, 0, 0);
if(arp){
rp->marker |= mark;
break;
}
}
/*
* if the cache and database lookup didn't find any new
* server addresses, try resolving one via the network.
* Mark any we try to resolve so we don't try a second time.
*/
if(arp == nil){
for(rp = qp->nsrp; rp; rp = rp->next)
if((rp->marker & mark) == 0)
if(queryloops(qp, rp))
/*
* give up as we should have got the address
* by higher up nameserver when recursing
* down, or will be queried when recursing up.
*/
return nd;
for(rp = qp->nsrp; rp; rp = rp->next){
if(rp->marker & mark)
continue;
rp->marker |= mark;
if(strncmp(rp->owner->name, "local#", 6) == 0)
continue;
arp = dnresolve(rp->host->name, Cin, type, qp->req, 0,
qp->depth+1, Recurse, 1, 0);
rrfreelist(rrremneg(&arp));
if(arp)
break;
}
}
/* use any addresses that we found */
for(trp = arp; trp && nd < Maxdest; trp = trp->next){
p = &dest[nd];
memset(p, 0, sizeof *p);
if(parseip(p->a, trp->ip->name) == -1)
continue;
if(ipcmp(p->a, IPnoaddr) == 0)
continue;
if(ipisbm(p->a))
continue;
if(cfg.serve && myip(p->a))
continue;
p->nx = 0;
p->n = nil;
p->s = trp->owner;
for(rp = qp->nsrp; rp; rp = rp->next){
if(rp->host == p->s){
p->n = rp;
break;
}
}
p->code = Rtimeout;
nd++;
}
rrfreelist(arp);
return nd;
}
/*
* cache negative responses
*/
static void
cacheneg(DN *dp, int type, int rcode, RR *soarr)
{
RR *rp;
DN *soaowner;
ulong ttl;
stats.negcached++;
/* no cache time specified, don't make anything up */
if(soarr != nil){
if(soarr->next != nil)
rrfreelistptr(&soarr->next);
soaowner = soarr->owner;
} else
soaowner = nil;
/* the attach can cause soarr to be freed so mine it now */
if(soarr != nil && soarr->soa != nil)
ttl = soarr->soa->minttl;
else
ttl = 5*Min;
/* add soa and negative RR to the database */
rrattach(soarr, Authoritative);
rp = rralloc(type);
rp->owner = dp;
rp->negative = 1;
rp->negsoaowner = soaowner;
rp->negrcode = rcode;
rp->ttl = ttl;
rrattach(rp, Authoritative);
}
static int
filterhints(RR *rp, void *arg)
{
RR *nsrp;
if(rp->type != Ta && rp->type != Taaaa)
return 0;
for(nsrp = arg; nsrp; nsrp = nsrp->next)
if(nsrp->type == Tns && rp->owner == nsrp->host)
return 1;
return 0;
}
static int
filterauth(RR *rp, void *arg)
{
Dest *dest;
RR *nsrp;
dest = arg;
nsrp = dest->n;
if(nsrp == nil)
return 0;
if(rp->type == Tsoa && rp->owner != nsrp->owner
&& !subsume(nsrp->owner->name, rp->owner->name)
&& strncmp(nsrp->owner->name, "local#", 6) != 0)
return 1;
if(rp->type != Tns)
return 0;
if(rp->owner != nsrp->owner
&& !subsume(nsrp->owner->name, rp->owner->name)
&& strncmp(nsrp->owner->name, "local#", 6) != 0)
return 1;
return baddelegation(rp, nsrp, dest->a);
}
static void
reportandfree(RR *l, char *note, Dest *p)
{
RR *rp;
while(rp = l){
l = l->next;
rp->next = nil;
if(debug)
dnslog("ignoring %s from %I/%s: %R",
note, p->a, p->s->name, rp);
rrfree(rp);
}
}
/* returns Answerr (-1) on errors, else number of answers, which can be zero. */
static int
procansw(Query *qp, Dest *p, DNSmsg *mp)
{
Query nq;
DN *ndp;
RR *tp, *soarr;
int rv, rcode;
if(mp->an == nil)
stats.negans++;
/* get extended rcode */
rcode = Rok;
mp->edns = getednsopt(mp, &rcode);
if(rcode == Rok)
rcode = getercode(mp);
rrfreelistptr(&mp->edns);
/* ignore any error replies */
switch(rcode){
case Rformat:
case Rrefused:
case Rserver:
case Rbadvers:
stats.negserver++;
freeanswers(mp);
p->code = Rserver;
return Answerr;
}
/* ignore any bad delegations */
if((tp = rrremfilter(&mp->ns, filterauth, p)) != 0)
reportandfree(tp, "bad delegation", p);
/* remove any soa's from the authority section */
soarr = rrremtype(&mp->ns, Tsoa);
/* only nameservers remaining */
if((tp = rrremtype(&mp->ns, Tns)) != 0){
reportandfree(mp->ns, "non-nameserver", p);
mp->ns = tp;
}
/* remove answers not related to the question. */
if((tp = rrremowner(&mp->an, qp->dp)) != 0){
reportandfree(mp->an, "wrong subject answer", p);
mp->an = tp;
}
if(qp->type != Tall){
if((tp = rrremtype(&mp->an, qp->type)) != 0){
reportandfree(mp->an, "wrong type answer", p);
mp->an = tp;
}
}
/* incorporate answers */
unique(mp->an);
unique(mp->ns);
unique(mp->ar);
if(mp->an){
/*
* only use cname answer when returned. some dns servers
* attach (potential) spam hint address records which poisons
* the cache.
*/
if((tp = rrremtype(&mp->an, Tcname)) != 0){
reportandfree(mp->an, "ip in cname answer", p);
mp->an = tp;
}
rrattach(mp->an, (mp->flags & Fauth) != 0);
}
if(mp->ar){
/* restrict hints to address rr's for nameservers only */
if((tp = rrremfilter(&mp->ar, filterhints, mp->ns)) != 0){
reportandfree(mp->ar, "hint", p);
mp->ar = tp;
}
rrattach(mp->ar, Notauthoritative);
}
if(mp->ns && !cfg.justforw){
ndp = mp->ns->owner;
rrattach(mp->ns, Notauthoritative);
} else {
ndp = nil;
rrfreelistptr(&mp->ns);
mp->nscount = 0;
}
/* free the question */
if(mp->qd) {
rrfreelistptr(&mp->qd);
mp->qdcount = 0;
}
/*
* Any reply from an authoritative server
* that does not provide more nameservers,
* or a positive reply terminates the search.
* A negative response now also terminates the search.
*/
if(mp->an || (mp->flags & Fauth) && mp->ns == nil){
if(mp->an == nil && rcode == Rname)
qp->dp->respcode = Rname;
else
qp->dp->respcode = Rok;
/*
* cache any negative responses, free soarr.
* negative responses need not be authoritative:
* they can legitimately come from a cache.
*/
if( /* (mp->flags & Fauth) && */ mp->an == nil)
cacheneg(qp->dp, qp->type, rcode, soarr);
else
rrfreelist(soarr);
return 1;
} else if (mp->an == nil && rcode == Rname) {
qp->dp->respcode = Rname;
/*
* cache negative response.
* negative responses need not be authoritative:
* they can legitimately come from a cache.
*/
cacheneg(qp->dp, qp->type, rcode, soarr);
return 1;
}
stats.negnorname++;
rrfreelist(soarr);
/*
* if we've been given better name servers, recurse.
* if we're a pure resolver, don't recurse, we have
* to forward to a fixed set of named servers.
*/
if(mp->ns == nil || cfg.resolver && cfg.justforw)
return Answnone;
tp = rrlookup(ndp, Tns, NOneg);
if(contains(qp->nsrp, tp)){
rrfreelist(tp);
return Answnone;
}
initquery(&nq, qp->dp, qp->type, qp->req, qp->depth+1);
rv = netqueryns(&nq, tp);
exitquery(&nq);
return rv;
}
static int
writenet(Query *qp, int medium, int fd, uchar *pkt, int len, Dest *p)
{
uchar tmp[2];
int rv;
logrequest(qp->req->id, qp->depth, "send", p->a, p->s->name,
qp->dp->name, qp->type);
rv = -1;
switch (medium) {
case Udp:
/* fill in UDP destination addr & send it */
ipmove(pkt, p->a);
if (write(fd, pkt, len+Udphdrsize) != len+Udphdrsize)
warning("sending udp msg to %I/%s: %r", p->a, p->s->name);
else {
stats.qsentudp++;
rv = 0;
}
break;
case Tcp:
tmp[0] = pkt[Udphdrsize-2], pkt[Udphdrsize-2] = len >> 8;
tmp[1] = pkt[Udphdrsize-1], pkt[Udphdrsize-1] = len;
len += 2;
if (write(fd, pkt + Udphdrsize-2, len) != len)
warning("sending tcp msg to %I/%s: %r", p->a, p->s->name);
else {
stats.qsenttcp++;
rv = 0;
}
pkt[Udphdrsize-2] = tmp[0];
pkt[Udphdrsize-1] = tmp[1];
break;
}
return rv;
}
/*
* send a query via tcp to a single address
* and read the answer(s) into mp->an.
*/
static int
tcpquery(Query *qp, uchar *pkt, int len, Dest *p, uvlong endms, DNSmsg *mp)
{
char buf[NETPATHLEN];
int fd, rv;
long ms;
memset(mp, 0, sizeof *mp);
ms = (long)(endms - nowms);
if(ms < Minreqtm)
return -1; /* takes too long */
if(ms > Maxtcpdialtm)
ms = Maxtcpdialtm;
procsetname("tcp query to %I/%s for %s %s", p->a, p->s->name,
qp->dp->name, rrname(qp->type, buf, sizeof buf));
snprint(buf, sizeof buf, "%s/tcp!%I!53", mntpt, p->a);
alarm(ms);
fd = dial(buf, nil, nil, nil);
alarm(0);
if (fd < 0) {
dnslog("%d: can't dial %s for %I/%s: %r",
qp->req->id, buf, p->a, p->s->name);
return -1;
}
rv = writenet(qp, Tcp, fd, pkt, len, p);
if(rv == 0){
timems(); /* account for time dialing and sending */
rv = readreply(qp, Tcp, fd, endms, mp, pkt);
}
close(fd);
return rv;
}
/*
* query name servers. fill in pkt with on-the-wire representation of a
* DNSmsg derived from qp. if the name server returns a pointer to another
* name server, recurse.
*/
static int
udpqueryns(Query *qp, int fd, uchar *pkt)
{
Dest dest[Maxdest], *edest, *p, *np;
int ndest, replywaits, len, flag, rv, n;
uchar srcip[IPaddrlen];
char buf[32];
uvlong endms;
DNSmsg m;
RR *rp;
/* prepare server RR's for incremental lookup */
for(rp = qp->nsrp; rp; rp = rp->next)
rp->marker = 0;
/* request recursion only for local dns servers */
flag = Oquery;
if(strncmp(qp->nsrp->owner->name, "local#", 6) == 0)
flag |= Frecurse;
/* pack request into a udp message */
qp->id = rand();
len = mkreq(qp->dp, qp->type, pkt, flag, qp->id);
/* no destination yet */
edest = dest;
/*
* transmit udp requests and wait for answers.
* at most Maxtrans attempts to each address.
* each cycle send one more message than the previous.
* retry a query via tcp if its response is truncated.
*/
for(ndest = 2; ndest < Maxdest; ndest += 2){
endms = nowms;
if((long)(qp->req->aborttime - nowms) < Minreqtm)
break;
/*
* get a nameserver address if we need one.
* we're to transmit to more destinations than we currently have,
* so get another.
*/
n = edest - dest;
if (n < ndest) {
/* populates dest with v4 and v6 addresses. */
n = serveraddrs(qp, dest, n, Ta);
n = serveraddrs(qp, dest, n, Taaaa);
edest = dest + n;
}
n = 0;
for(p = dest; p < edest && p < &dest[ndest]; p++){
/* skip destinations we've finished with */
if(p->nx >= Maxtrans)
continue;
/* exponential backoff of requests */
if((1UL<<p->nx) > ndest)
continue;
p->nx++;
if(writenet(qp, Udp, fd, pkt, len, p) < 0)
continue;
n++;
}
/* nothing left to send to */
if (n == 0)
break;
/* set the timeout for replies */
endms += 500;
if(endms > qp->req->aborttime)
endms = qp->req->aborttime;
procsetname("reading replies from %I...: %s %s from %s",
pkt, qp->dp->name,
rrname(qp->type, buf, sizeof buf), qp->req->from);
for(replywaits = 0; replywaits < ndest; replywaits++){
/* read udp answer into m, fill srcip */
if(readreply(qp, Udp, fd, endms, &m, srcip) < 0)
break;
/* find responder */
for(p = dest; p < edest; p++)
if(ipcmp(p->a, srcip) == 0)
break;
if(p >= edest){
freeanswers(&m);
continue;
}
/* if response was truncated, try tcp */
if(m.flags & Ftrunc){
freeanswers(&m);
if(tcpquery(qp, pkt, len, p, endms, &m) < 0)
break; /* failed via tcp too */
if(m.flags & Ftrunc){
freeanswers(&m);
break;
}
}
/* remove all addrs of responding server from list */
for(np = dest; np < edest; np++)
if(np->s == p->s)
np->nx = Maxtrans;
/* free or incorporate RRs in m */
rv = procansw(qp, p, &m);
if(rv > Answnone)
return rv;
}
}
/* if all servers returned failure, propagate it */
qp->dp->respcode = Rserver;
for(p = dest; p < edest; p++)
if(p->code != Rserver)
qp->dp->respcode = Rok;
return Answnone;
}
/*
* in principle we could use a single descriptor for a udp port
* to send all queries and receive all the answers to them,
* but we'd have to sort out the answers by dns-query id.
*/
static int
udpquery(Query *qp)
{
int fd, rv;
uchar *pkt;
pkt = emalloc(Maxudp+Udphdrsize);
fd = udpport(mntpt);
if (fd < 0) {
dnslog("%d: can't get udpport for %s query of name %s: %r",
qp->req->id, mntpt, qp->dp->name);
rv = -1;
goto Out;
}
rv = udpqueryns(qp, fd, pkt);
close(fd);
Out:
free(pkt);
return rv;
}
/*
* look up (qp->dp->name, qp->type) rr in dns,
* using nameservers in qp->nsrp.
*/
static int
netquery(Query *qp)
{
if(qp->depth > 12) /* in a recursive loop? */
return Answnone;
slave(qp->req);
/*
* slave might have forked. if so, the parent process longjmped to
* req->mret; we're usually the child slave, but if there are too
* many children already, we're still the same process. under no
* circumstances block the 9p loop.
*/
if(!qp->req->isslave && strcmp(qp->req->from, "9p") == 0)
return Answnone;
return udpquery(qp);
}