ref: a3b95d3e567c0ef60f9f1ead26124fb706dec20d
dir: /sys/src/cmd/upas/smtp/mxdial.c/
#include "common.h"
#include "smtp.h"
#include <ndb.h>
char *bustedmxs[Maxbustedmx];
static void
expand(DS *ds)
{
char *s;
Ndbtuple *t;
s = ds->host + 1;
t = csipinfo(ds->netdir, "sys", sysname(), &s, 1);
if(t != nil){
strecpy(ds->expand, ds->expand+sizeof ds->expand, t->val);
ds->host = ds->expand;
}
ndbfree(t);
}
/* break up an address to its component parts */
void
dialstringparse(char *str, DS *ds)
{
char *p, *p2;
strecpy(ds->buf, ds->buf + sizeof ds->buf, str);
p = strchr(ds->buf, '!');
if(p == 0) {
ds->netdir = 0;
ds->proto = "net";
ds->host = ds->buf;
} else {
if(*ds->buf != '/'){
ds->netdir = 0;
ds->proto = ds->buf;
} else {
for(p2 = p; *p2 != '/'; p2--)
;
*p2++ = 0;
ds->netdir = ds->buf;
ds->proto = p2;
}
*p = 0;
ds->host = p + 1;
}
ds->service = strchr(ds->host, '!');
if(ds->service)
*ds->service++ = 0;
else
ds->service = "smtp";
if(*ds->host == '$')
expand(ds);
}
void
mxtabfree(Mxtab *mx)
{
free(mx->mx);
memset(mx, 0, sizeof *mx);
}
static void
mxtabrealloc(Mxtab *mx)
{
if(mx->nmx < mx->amx)
return;
if(mx->amx == 0)
mx->amx = 1;
mx->amx <<= 1;
mx->mx = realloc(mx->mx, sizeof mx->mx[0] * mx->amx);
if(mx->mx == nil)
sysfatal("no memory for mx");
}
static void
mxtabadd(Mxtab *mx, char *host, char *ip, char *net, int pref)
{
int i;
Mx *x;
mxtabrealloc(mx);
x = mx->mx;
for(i = mx->nmx; i>0 && x[i-1].pref>pref && x[i-1].netdir == net; i--)
x[i] = x[i-1];
strecpy(x[i].host, x[i].host + sizeof x[i].host, host);
if(ip != nil)
strecpy(x[i].ip, x[i].ip + sizeof x[i].ip, ip);
else
x[i].ip[0] = 0;
x[i].netdir = net;
x[i].pref = pref;
x[i].valid = 1;
mx->nmx++;
}
static int
timeout(void*, char *msg)
{
if(strstr(msg, "alarm"))
return 1;
return 0;
}
static long
timedwrite(int fd, void *buf, long len, long ms)
{
long n, oalarm;
atnotify(timeout, 1);
oalarm = alarm(ms);
n = pwrite(fd, buf, len, 0);
alarm(oalarm);
atnotify(timeout, 0);
return n;
}
static int
dnslookup(Mxtab *mx, int fd, char *query, char *domain, char *net, int pref0)
{
int n;
char buf[1024], *f[4];
n = timedwrite(fd, query, strlen(query), 60*1000);
if(n < 0){
rerrstr(buf, sizeof buf);
dprint("dns: %s\n", buf);
if(strstr(buf, "dns failure")){
/* if dns fails for the mx lookup, we have to stop */
close(fd);
return -1;
}
return 0;
}
seek(fd, 0, 0);
for(;;){
if((n = read(fd, buf, sizeof buf - 1)) < 1)
break;
buf[n] = 0;
// chat("dns: %s\n", buf);
n = tokenize(buf, f, nelem(f));
if(n < 2)
continue;
if(strcmp(f[1], "mx") == 0 && n == 4){
if(strchr(domain, '.') == 0)
strcpy(domain, f[0]);
mxtabadd(mx, f[3], nil, net, atoi(f[2]));
}
else if (strcmp(f[1], "ip") == 0 && n == 3){
if(strchr(domain, '.') == 0)
strcpy(domain, f[0]);
mxtabadd(mx, f[0], f[2], net, pref0);
}
}
return 0;
}
static int
busted(char *mx)
{
char **bmp;
for (bmp = bustedmxs; *bmp != nil; bmp++)
if (strcmp(mx, *bmp) == 0)
return 1;
return 0;
}
static void
complain(Mxtab *mx, char *domain)
{
char buf[1024], *e, *p;
int i;
p = buf;
e = buf + sizeof buf;
for(i = 0; i < mx->nmx; i++)
p = seprint(p, e, "%s ", mx->mx[i].ip);
syslog(0, "smtpd.mx", "loopback for %s %s", domain, buf);
}
static int
okaymx(Mxtab *mx, char *domain)
{
int i;
Mx *x;
/* look for malicious dns entries; TODO use badcidr in ../spf/ to catch more than ip4 */
for(i = 0; i < mx->nmx; i++){
x = mx->mx + i;
if(x->valid && strcmp(x->ip, "127.0.0.1") == 0){
dprint("illegal: domain %s lists 127.0.0.1 as mail server", domain);
complain(mx, domain);
werrstr("illegal: domain %s lists 127.0.0.1 as mail server", domain);
return -1;
}
if(x->valid && busted(x->host)){
dprint("lookup: skipping busted mx %s\n", x->host);
x->valid = 0;
}
}
return 0;
}
static int
lookup(Mxtab *mx, char *net, char *host, char *domain, char *type)
{
char dns[128], buf[1024];
int fd, i;
Mx *x;
snprint(dns, sizeof dns, "%s/dns", net);
fd = open(dns, ORDWR);
if(fd == -1)
return -1;
snprint(buf, sizeof buf, "%s %s", host, type);
dprint("sending %s '%s'\n", dns, buf);
dnslookup(mx, fd, buf, domain, net, 10000);
for(i = 0; i < mx->nmx; i++){
x = mx->mx + i;
if(x->ip[0] != 0)
continue;
x->valid = 0;
snprint(buf, sizeof buf, "%s %s", x->host, "ip");
dprint("sending %s '%s'\n", dns, buf);
dnslookup(mx, fd, buf, domain, net, x->pref);
}
close(fd);
if(strcmp(type, "mx") == 0){
if(okaymx(mx, domain) == -1)
return -1;
for(i = 0; i < mx->nmx; i++){
x = mx->mx + i;
dprint("mx list: %s %d %s\n", x->host, x->pref, x->ip);
}
dprint("\n");
}
return 0;
}
static int
lookcall(Mxtab *mx, DS *d, char *domain, char *type)
{
char buf[1024];
int i;
Mx *x;
if(lookup(mx, d->netdir, d->host, domain, type) == -1){
for(i = 0; i < mx->nmx; i++)
if(mx->mx[i].netdir == d->netdir)
mx->mx[i].valid = 0;
return -1;
}
for(i = 0; i < mx->nmx; i++){
x = mx->mx + i;
if(x->ip[0] == 0 || x->valid == 0){
x->valid = 0;
continue;
}
snprint(buf, sizeof buf, "%s/%s!%s!%s", d->netdir, d->proto,
x->ip /*x->host*/, d->service);
dprint("mxdial trying %s [%s]\n", x->host, buf);
atnotify(timeout, 1);
alarm(10*1000);
mx->fd = dial(buf, 0, 0, 0);
alarm(0);
atnotify(timeout, 0);
if(mx->fd >= 0){
mx->pmx = i;
return mx->fd;
}
dprint(" failed %r\n");
x->valid = 0;
}
return -1;
}
int
mxdial0(char *addr, char *ddomain, char *gdomain, Mxtab *mx)
{
int nd, i, j;
DS *d;
static char *tab[] = {"mx", "ip", };
dprint("mxdial(%s, %s, %s, mx)\n", addr, ddomain, gdomain);
memset(mx, 0, sizeof *mx);
d = mx->ds;
dialstringparse(addr, d + 0);
nd = 1;
if(d[0].netdir == nil){
d[1] = d[0];
d[0].netdir = "/net";
d[1].netdir = "/net.alt";
nd = 2;
}
/* search all networks for mx records; then ip records */
for(j = 0; j < nelem(tab); j++)
for(i = 0; i < nd; i++)
if(lookcall(mx, d + i, ddomain, tab[j]) != -1)
return mx->fd;
/* grotty: try gateway machine by ip only (fixme: try cs lookup) */
if(gdomain != nil){
dialstringparse(netmkaddr(gdomain, 0, "smtp"), d + 0);
if(lookcall(mx, d + 0, gdomain, "ip") != -1)
return mx->fd;
}
return -1;
}
int
mxdial(char *addr, char *ddomain, char *gdomain, Mx *x)
{
int fd;
Mxtab mx;
memset(x, 0, sizeof *x);
fd = mxdial0(addr, ddomain, gdomain, &mx);
if(fd >= 0 && mx.pmx >= 0)
*x = mx.mx[mx.pmx];
mxtabfree(&mx);
return fd;
}