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plugin-chkdns.c
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plugin-chkdns.c
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/*
* Make DNS checks on envelope data
* Check that domain in MAIL FROM has MX, A, or AAAA record
* Check HELO, MAIL FROM against DBLLOOKUP domain
*
* Has to come before anything that might accept a sender
* everything except non-existent MAIL FROM sends mail to sump
* or rejects if DBLREJECT is set
*
*/
#include <stdlib.h>
#include <unistd.h>
#include "mailfront.h"
#include <sys/types.h>
#include <netinet/in.h>
#include <arpa/nameser.h>
#include <resolv.h>
#include <msg/msg.h>
static RESPONSE(badfrom,553,"5.1.8 Invalid sender domain.");
static response resp_baddbl = { 553, "???" };
static int dblchk(str *domain, str *dbltxt)
{
str dblstr;
char *dbl = getenv("DBLLOOKUP");
int l, i;
unsigned char ansbuf[512];
if(!dbl || domain->len == 0) return 0;
if(session_getnum("sump",0)) return 0; /* no point */
str_init(&dblstr);
str_copy(&dblstr, domain);
str_catc(&dblstr, '.');
str_cats(&dblstr, dbl);
l = res_query(dblstr.s, C_IN, T_TXT, ansbuf, sizeof(ansbuf));
if(l > 0 && ((HEADER *)ansbuf)->ancount != 0) { /* something in the answer */
unsigned char *recbuf = ansbuf+NS_HFIXEDSZ;
/* skip over questions, why am I still writing stuff
* like this? */
for(i = ns_get16(ansbuf+4); i != 0; --i)
recbuf += dn_skipname(recbuf, ansbuf+l)+4;
for(i = ns_get16(ansbuf+6); i != 0; --i) {
recbuf += dn_skipname(recbuf, ansbuf+l);
if(ns_get16(recbuf) != T_TXT) { /* CNAME or something */
recbuf += 10 + ns_get16(recbuf+8);
continue;
}
/* it's a TXT record, wow */
str_init(dbltxt);
str_copyb(dbltxt, (char*)recbuf+11, recbuf[10]);
str_free(&dblstr);
return 1;
}
} /* didn't find anything */
str_free(&dblstr);
return 0;
}
static const response* chkdns_helo(str* hostname, str* capabilities)
{
str dbltxt;
/* hack, don't check numeric, guess from first character */
if(hostname->s[0] >= '0' && hostname->s[0] <= '9') return 0;
if(dblchk(hostname, &dbltxt)) {
session_setenv("RBLSMTPD", dbltxt.s, 0);
session_setnum("dblhelo", 1);
session_setnum("sump", 1);
msg4("HELO ", hostname->s, " in DBL ",dbltxt.s);
if(getenv("DBLREJECT")) {
resp_baddbl.message = dbltxt.s;
return &resp_baddbl;
}
}
return 0;
(void) capabilities;
}
/* check sender domain */
static const response* chkdns_sender(str* sender, str* params)
{
str domstr, dbltxt;
int i;
unsigned char ansbuf[512];
if(sender->len == 0) return 0; /* bounce */
i = str_findlast(sender, '@');
if(i < 0) {
return &resp_badfrom; /* no domain */
}
str_init(&domstr);
str_copyb(&domstr, sender->s+i+1, sender->len-i-1);
if(domstr.len == 0) { /* null domain */
str_free(&domstr);
return &resp_badfrom;
}
/* first check dbl */
if(dblchk(&domstr, &dbltxt)) {
session_setenv("RBLSMTPD", dbltxt.s, 0);
session_setnum("dblfrom", 1);
session_setnum("sump", 1);
msg2("MAIL FROM in DBL ",dbltxt.s);
str_free(&domstr);
if(getenv("DBLREJECT")) {
resp_baddbl.message = dbltxt.s;
return &resp_baddbl;
}
return 0;
}
i = res_query(domstr.s, C_IN, T_MX, ansbuf, sizeof(ansbuf));
if(i > 0 && ((HEADER *)ansbuf)->ancount != 0) { /* has an MX */
str_free(&domstr);
return 0;
}
i = res_query(domstr.s, C_IN, T_A, ansbuf, sizeof(ansbuf));
if(i > 0 && ((HEADER *)ansbuf)->ancount != 0) { /* has an A */
str_free(&domstr);
return 0;
}
i = res_query(domstr.s, C_IN, T_AAAA, ansbuf, sizeof(ansbuf));
str_free(&domstr);
if(i > 0 && ((HEADER *)ansbuf)->ancount != 0) return 0; /* has an AAAA */
return &resp_badfrom;
(void)params;
}
struct plugin plugin = {
.version = PLUGIN_VERSION,
.flags = 0,
.helo = chkdns_helo,
.sender = chkdns_sender,
};