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/*
* checkalias.c -- check to see if two hostnames or IP addresses are equivalent
*
* Copyright 1997 by Eric S. Raymond
* For license terms, see the file COPYING in this directory.
*/
#include "config.h"
#ifdef HAVE_GETHOSTBYNAME
#include <stdio.h>
#include <string.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <netdb.h>
#include "mx.h"
#include "fetchmail.h"
#define MX_RETRIES 3
static int is_ip_alias(const char *name1,const char *name2)
/*
* Given two hostnames as arguments, returns TRUE if they
* have at least one IP address in common.
* No check is done on errors returned by gethostbyname,
* the calling function does them.
*/
{
typedef unsigned char address_t[sizeof (struct in_addr)];
typedef struct _address_e
{
struct _address_e *next;
address_t address;
}
address_e;
address_e *host_a_addr, *host_b_addr,*dummy_addr;
int i;
struct hostent *hp;
char **p;
hp = gethostbyname(name1);
dummy_addr = (address_e *)NULL;
for (i=0,p = hp->h_addr_list; *p != 0; i++,p++)
{
struct in_addr in;
(void) memcpy(&in.s_addr, *p, sizeof (in.s_addr));
xalloca(host_a_addr, address_e *, sizeof (address_e));
memset (host_a_addr,0, sizeof (address_e));
host_a_addr->next = dummy_addr;
(void) memcpy(&host_a_addr->address, *p, sizeof (in.s_addr));
dummy_addr = host_a_addr;
}
hp = gethostbyname(name2);
dummy_addr = (address_e *)NULL;
for (i=0,p = hp->h_addr_list; *p != 0; i++,p++)
{
struct in_addr in;
(void) memcpy(&in.s_addr, *p, sizeof (in.s_addr));
xalloca(host_b_addr, address_e *, sizeof (address_e));
memset (host_b_addr,0, sizeof (address_e));
host_b_addr->next = dummy_addr;
(void) memcpy(&host_b_addr->address, *p, sizeof (in.s_addr));
dummy_addr = host_b_addr;
}
while (host_a_addr)
{
while (host_b_addr)
{
if (!memcmp(host_b_addr->address,host_a_addr->address, sizeof (address_t)))
return (TRUE);
host_b_addr = host_b_addr->next;
}
host_a_addr = host_a_addr->next;
}
return (FALSE);
}
int is_host_alias(const char *name, struct query *ctl)
/* determine whether name is a DNS alias of the mailserver for this query */
{
struct hostent *he,*he_st;
struct mxentry *mxp, *mxrecords;
struct hostdata *lead_server =
ctl->server.lead_server ? ctl->server.lead_server : &ctl->server;
/*
* The first two checks are optimizations that will catch a good
* many cases.
*
* (1) check against the `true name' deduced from the poll label
* and the via option (if present) at the beginning of the poll cycle.
* Odds are good this will either be the mailserver's FQDN or a suffix of
* it with the mailserver's domain's default host name omitted.
*
* (2) Then check the rest of the `also known as'
* cache accumulated by previous DNS checks. This cache is primed
* by the aka list option.
*
* Any of these on a mail address is definitive. Only if the
* name doesn't match any is it time to call the bind library.
* If this happens odds are good we're looking at an MX name.
*/
if (strcasecmp(lead_server->truename, name) == 0)
return(TRUE);
else if (str_in_list(&lead_server->akalist, name, TRUE))
return(TRUE);
else if (!ctl->server.dns)
return(FALSE);
#ifndef HAVE_RES_SEARCH
return(FALSE);
#else
/*
* The only code that calls the BIND library is here and in the
* start-of-run probe with gethostbyname(3) under ETRN/Kerberos.
*
* We know DNS service was up at the beginning of the run.
* If it's down, our nameserver has crashed. We don't want to try
* delivering the current message or anything else from the
* current server until it's back up.
*/
else if ((he = gethostbyname(name)) != (struct hostent *)NULL)
{
if (strcasecmp(ctl->server.truename, he->h_name) == 0)
goto match;
else if (((he_st = gethostbyname(ctl->server.truename)) != (struct hostent *)NULL) && ctl->server.checkalias)
{
if (outlevel >= O_DEBUG)
error(0, 0, "Checking if %s is really the same node as %s",ctl->server.truename,name);
if (is_ip_alias(ctl->server.truename,name) == TRUE)
{
if (outlevel >= O_DEBUG)
error(0, 0, "Yes, their IP addresses match");
goto match;
}
if (outlevel >= O_DEBUG)
error(0, 0, "No, their IP addresses don't match");
}
else
return(FALSE);
}
else
switch (h_errno)
{
case HOST_NOT_FOUND: /* specified host is unknown */
case NO_ADDRESS: /* valid, but does not have an IP address */
break;
case NO_RECOVERY: /* non-recoverable name server error */
case TRY_AGAIN: /* temporary error on authoritative server */
default:
if (outlevel != O_SILENT)
putchar('\n'); /* terminate the progress message */
error(0, 0,
"nameserver failure while looking for `%s' during poll of %s.",
name, ctl->server.pollname);
ctl->errcount++;
break;
}
/*
* We're only here if DNS was OK but the gethostbyname() failed
* with a HOST_NOT_FOUND or NO_ADDRESS error.
* Search for a name match on MX records pointing to the server.
*/
h_errno = 0;
if ((mxrecords = getmxrecords(name)) == (struct mxentry *)NULL)
{
switch (h_errno)
{
case HOST_NOT_FOUND: /* specified host is unknown */
case NO_ADDRESS: /* valid, but does not have an IP address */
return(FALSE);
break;
case NO_RECOVERY: /* non-recoverable name server error */
case TRY_AGAIN: /* temporary error on authoritative server */
default:
error(0, -1,
"nameserver failure while looking for `%s' during poll of %s.",
name, ctl->server.pollname);
ctl->errcount++;
break;
}
}
else
{
for (mxp = mxrecords; mxp->name; mxp++)
if (strcasecmp(ctl->server.truename, mxp->name) == 0)
goto match;
return(FALSE);
match:;
}
/* add this name to relevant server's `also known as' list */
save_str(&lead_server->akalist, name, 0);
return(TRUE);
#endif /* HAVE_RES_SEARCH */
}
#endif /* HAVE_GETHOSTBYNAME */
/* checkalias.c ends here */
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