ref: ed9fdc72f519553f9c8f1f221f97bd5919847caa
dir: /sys/src/cmd/upas/smtp/mxdial.c/
#include "common.h"
#include <ndb.h>
#include <smtp.h> /* to publish dial_string_parse */
enum
{
Nmx= 16,
Maxstring= 256,
};
typedef struct Mx Mx;
struct Mx
{
char host[256];
char ip[24];
int pref;
};
char *bustedmxs[Maxbustedmx];
Ndb *db;
static int mxlookup(DS*, char*);
static int mxlookup1(DS*, char*);
static int compar(void*, void*);
static int callmx(DS*, char*, char*);
static void expand_meta(DS *ds);
static Mx mx[Nmx];
int
mxdial(char *addr, char *ddomain, char *gdomain)
{
int fd;
DS ds;
addr = netmkaddr(addr, 0, "smtp");
dial_string_parse(addr, &ds);
/* try connecting to destination or any of it's mail routers */
fd = callmx(&ds, addr, ddomain);
/* try our mail gateway */
if(fd < 0 && gdomain)
fd = dial(netmkaddr(gdomain, 0, "smtp"), 0, 0, 0);
return fd;
}
static int
busted(char *mx)
{
char **bmp;
for (bmp = bustedmxs; *bmp != nil; bmp++)
if (strcmp(mx, *bmp) == 0)
return 1;
return 0;
}
static int
timeout(void*, char *msg)
{
if(strstr(msg, "alarm"))
return 1;
return 0;
}
long
timedwrite(int fd, void *buf, long len, long ms)
{
long n, oalarm;
atnotify(timeout, 1);
oalarm = alarm(ms);
n = write(fd, buf, len);
alarm(oalarm);
atnotify(timeout, 0);
return n;
}
/*
* take an address and return all the mx entries for it,
* most preferred first
*/
static int
callmx(DS *ds, char *dest, char *domain)
{
int fd, i, nmx;
char addr[Maxstring];
/* get a list of mx entries */
nmx = mxlookup(ds, domain);
if(nmx < 0){
/* dns isn't working, don't just dial */
return -1;
}
if(nmx == 0){
if(debug)
fprint(2, "mxlookup returns nothing\n");
return dial(dest, 0, 0, 0);
}
/* refuse to honor loopback addresses given by dns */
for(i = 0; i < nmx; i++)
if(strcmp(mx[i].ip, "127.0.0.1") == 0){
if(debug)
fprint(2, "mxlookup returns loopback\n");
werrstr("illegal: domain lists 127.0.0.1 as mail server");
return -1;
}
/* sort by preference */
if(nmx > 1)
qsort(mx, nmx, sizeof(Mx), compar);
/* dial each one in turn */
for(i = 0; i < nmx; i++){
if (busted(mx[i].host)) {
if (debug)
fprint(2, "mxdial skipping busted mx %s\n",
mx[i].host);
continue;
}
snprint(addr, sizeof(addr), "%s/%s!%s!%s", ds->netdir, ds->proto,
mx[i].host, ds->service);
if(debug)
fprint(2, "mxdial trying %s\n", addr);
atnotify(timeout, 1);
alarm(10*1000);
fd = dial(addr, 0, 0, 0);
alarm(0);
atnotify(timeout, 0);
if(fd >= 0)
return fd;
}
return -1;
}
/*
* call the dns process and have it try to resolve the mx request
*
* this routine knows about the firewall and tries inside and outside
* dns's seperately.
*/
static int
mxlookup(DS *ds, char *domain)
{
int n;
/* just in case we find no domain name */
strcpy(domain, ds->host);
if(ds->netdir)
n = mxlookup1(ds, domain);
else {
ds->netdir = "/net";
n = mxlookup1(ds, domain);
if(n <= 0) {
ds->netdir = "/net.alt";
n = mxlookup1(ds, domain);
}
}
return n;
}
static int
mxlookup1(DS *ds, char *domain)
{
int i, n, fd, nmx;
char buf[1024], dnsname[Maxstring];
char *fields[4];
snprint(dnsname, sizeof dnsname, "%s/dns", ds->netdir);
fd = open(dnsname, ORDWR);
if(fd < 0)
return 0;
nmx = 0;
snprint(buf, sizeof buf, "%s mx", ds->host);
if(debug)
fprint(2, "sending %s '%s'\n", dnsname, buf);
/*
* don't hang indefinitely in the write to /net/dns.
*/
n = timedwrite(fd, buf, strlen(buf), 60*1000);
if(n < 0){
rerrstr(buf, sizeof buf);
if(debug)
fprint(2, "dns: %s\n", buf);
if(strstr(buf, "dns failure")){
/* if dns fails for the mx lookup, we have to stop */
close(fd);
return -1;
}
} else {
/*
* get any mx entries
*/
seek(fd, 0, 0);
while(nmx < Nmx && (n = read(fd, buf, sizeof buf-1)) > 0){
buf[n] = 0;
if(debug)
fprint(2, "dns mx: %s\n", buf);
n = getfields(buf, fields, 4, 1, " \t");
if(n < 4)
continue;
if(strchr(domain, '.') == 0)
strcpy(domain, fields[0]);
strncpy(mx[nmx].host, fields[3], sizeof(mx[n].host)-1);
mx[nmx].pref = atoi(fields[2]);
nmx++;
}
if(debug)
fprint(2, "dns mx; got %d entries\n", nmx);
}
/*
* no mx record? try name itself.
*/
/*
* BUG? If domain has no dots, then we used to look up ds->host
* but return domain instead of ds->host in the list. Now we return
* ds->host. What will this break?
*/
if(nmx == 0){
mx[0].pref = 1;
strncpy(mx[0].host, ds->host, sizeof(mx[0].host));
nmx++;
}
/*
* look up all ip addresses
*/
for(i = 0; i < nmx; i++){
seek(fd, 0, 0);
snprint(buf, sizeof buf, "%s ip", mx[i].host);
mx[i].ip[0] = 0;
/*
* don't hang indefinitely in the write to /net/dns.
*/
if(timedwrite(fd, buf, strlen(buf), 60*1000) < 0)
goto no;
seek(fd, 0, 0);
if((n = read(fd, buf, sizeof buf-1)) < 0)
goto no;
buf[n] = 0;
if(getfields(buf, fields, 4, 1, " \t") < 3)
goto no;
strncpy(mx[i].ip, fields[2], sizeof(mx[i].ip)-1);
continue;
no:
/* remove mx[i] and go around again */
nmx--;
mx[i] = mx[nmx];
i--;
}
return nmx;
}
static int
compar(void *a, void *b)
{
return ((Mx*)a)->pref - ((Mx*)b)->pref;
}
/* break up an address to its component parts */
void
dial_string_parse(char *str, DS *ds)
{
char *p, *p2;
strncpy(ds->buf, str, sizeof(ds->buf));
ds->buf[sizeof(ds->buf)-1] = 0;
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;
if(*ds->host == '$')
expand_meta(ds);
}
static void
expand_meta(DS *ds)
{
char buf[128], cs[128], *net, *p;
int fd, n;
net = ds->netdir;
if(!net)
net = "/net";
if(debug)
fprint(2, "expanding %s!%s\n", net, ds->host);
snprint(cs, sizeof(cs), "%s/cs", net);
if((fd = open(cs, ORDWR)) == -1){
if(debug)
fprint(2, "open %s: %r\n", cs);
syslog(0, "smtp", "cannot open %s: %r", cs);
return;
}
snprint(buf, sizeof buf, "!ipinfo %s", ds->host+1); // +1 to skip $
if(write(fd, buf, strlen(buf)) <= 0){
if(debug)
fprint(2, "write %s: %r\n", cs);
syslog(0, "smtp", "%s to %s - write failed: %r", buf, cs);
close(fd);
return;
}
seek(fd, 0, 0);
if((n = read(fd, ds->expand, sizeof(ds->expand)-1)) < 0){
if(debug)
fprint(2, "read %s: %r\n", cs);
syslog(0, "smtp", "%s - read failed: %r", cs);
close(fd);
return;
}
close(fd);
ds->expand[n] = 0;
if((p = strchr(ds->expand, '=')) == nil){
if(debug)
fprint(2, "response %s: %s\n", cs, ds->expand);
syslog(0, "smtp", "%q from %s - bad response: %r", ds->expand, cs);
return;
}
ds->host = p+1;
/* take only first one returned (quasi-bug) */
if((p = strchr(ds->host, ' ')) != nil)
*p = 0;
}