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/*++
/* NAME
/* verify_sender_addr 3
/* SUMMARY
/* time-dependent probe sender addresses
/* SYNOPSIS
/* #include <verify_sender_addr.h>
/*
/* char *var_verify_sender;
/* int var_verify_sender_ttl;
/*
/* const char *make_verify_sender_addr()
/*
/* const char *valid_verify_sender_addr(addr)
/* const char *addr;
/* DESCRIPTION
/* This module computes or verifies a constant or time-dependent
/* sender address for an address verification probe. The
/* time-dependent portion is appended to the address localpart
/* specified with the address_verify_sender parameter.
/*
/* When the address_verify_sender parameter is empty or <>,
/* the sender address is always the empty address (i.e. always
/* time-independent).
/*
/* The caller must initialize the address_verify_sender and
/* address_verify_sender_ttl parameter values.
/*
/* make_verify_sender_addr() generates an envelope sender
/* address for an address verification probe.
/*
/* valid_verify_sender_addr() verifies that the given address
/* is a valid sender address for address verification probes.
/* When probe sender addresses are configured to be time-dependent,
/* the given address is allowed to differ by +/-1 TTL unit
/* from the expected address. The result is a null pointer
/* when no match is found. Otherwise, the result is the sender
/* address without the time-dependent portion; this is the
/* address that should be used for further delivery.
/* DIAGNOSTICS
/* Fatal errors: malformed address_verify_sender value; out
/* of memory.
/* LICENSE
/* .ad
/* .fi
/* The Secure Mailer license must be distributed with this software.
/* AUTHOR(S)
/* Wietse Venema
/* IBM T.J. Watson Research
/* P.O. Box 704
/* Yorktown Heights, NY 10598, USA
/*--*/
/* System library. */
#include <sys_defs.h>
#include <errno.h>
#include <string.h>
#include <stdlib.h>
/* Utility library. */
#include <msg.h>
#include <vstring.h>
#include <events.h>
#include <stringops.h>
/* Global library */
#include <mail_params.h>
#include <rewrite_clnt.h>
#include <safe_ultostr.h>
#include <verify_sender_addr.h>
/* Application-specific. */
/*
* We convert the time-dependent portion to a safe string (no vowels) in a
* reversible manner, so that we can check an incoming address against the
* current and +/-1 TTL time slot. This allows for some time slippage
* between multiple MTAs that handle mail for the same site. We use base 31
* so that the time stamp contains B-Z0-9. This simplifies regression tests.
*/
#define VERIFY_BASE 31
/*
* We append the time-dependent portion to the localpart of the the address
* verification probe sender address, so that the result has the form
* ``fixed1variable@fixed2''. There is no delimiter between ``fixed1'' and
* ``variable'', because that could make "old" time stamps valid depending
* on how the recipient_delimiter feature is configured. The fixed text is
* taken from var_verify_sender with perhaps domain information appended
* during address canonicalization. The variable part of the address changes
* every var_verify_sender_ttl seconds.
*/
char *var_verify_sender; /* "bare" probe sender address */
int var_verify_sender_ttl; /* time between address changes */
/*
* Scaffolding for stand-alone testing.
*/
#ifdef TEST
#undef event_time
#define event_time() verify_time
static unsigned long verify_time;
#endif
#define VERIFY_SENDER_ADDR_EPOCH() (event_time() / var_verify_sender_ttl)
/*
* SLMs.
*/
#define STR(x) vstring_str(x)
#define LEN(x) VSTRING_LEN(x)
/* make_verify_sender_addr - generate address_verify_sender address */
const char *make_verify_sender_addr(void)
{
static VSTRING *verify_sender_buf; /* the complete sender address */
static VSTRING *my_epoch_buf; /* scratch space */
char *my_at_domain;
/*
* The null sender is always time-independent.
*/
if (*var_verify_sender == 0 || strcmp(var_verify_sender, "<>") == 0)
return ("");
/*
* Sanity check.
*/
if (*var_verify_sender == '@')
msg_fatal("parameter %s: value \"%s\" must not start with '@'",
VAR_VERIFY_SENDER, var_verify_sender);
if ((my_at_domain = strchr(var_verify_sender, '@')) != 0 && my_at_domain[1] == 0)
msg_fatal("parameter %s: value \"%s\" must not end with '@'",
VAR_VERIFY_SENDER, var_verify_sender);
/*
* One-time initialization.
*/
if (verify_sender_buf == 0) {
verify_sender_buf = vstring_alloc(10);
my_epoch_buf = vstring_alloc(10);
}
/*
* Start with the bare sender address.
*/
vstring_strcpy(verify_sender_buf, var_verify_sender);
/*
* Append the time stamp to the address localpart, encoded in some
* non-decimal form for obscurity.
*
* XXX It would be nice to have safe_ultostr() append-only support.
*/
if (var_verify_sender_ttl > 0) {
/* Strip the @domain portion, if applicable. */
if (my_at_domain != 0)
vstring_truncate(verify_sender_buf,
(ssize_t) (my_at_domain - var_verify_sender));
/* Append the time stamp to the address localpart. */
vstring_sprintf_append(verify_sender_buf, "%s",
safe_ultostr(my_epoch_buf,
VERIFY_SENDER_ADDR_EPOCH(),
VERIFY_BASE, 0, 0));
/* Add back the @domain, if applicable. */
if (my_at_domain != 0)
vstring_sprintf_append(verify_sender_buf, "%s", my_at_domain);
}
/*
* Rewrite the address to canonical form.
*/
rewrite_clnt_internal(MAIL_ATTR_RWR_LOCAL, STR(verify_sender_buf),
verify_sender_buf);
return (STR(verify_sender_buf));
}
/* valid_verify_sender_addr - decide if address matches time window +/-1 */
const char *valid_verify_sender_addr(const char *their_addr)
{
static VSTRING *time_indep_sender_buf; /* sender without time stamp */
ssize_t base_len;
unsigned long my_epoch;
unsigned long their_epoch;
char *my_at_domain;
char *their_at_domain;
char *cp;
/*
* The null address is always time-independent.
*/
if (*var_verify_sender == 0 || strcmp(var_verify_sender, "<>") == 0)
return (*their_addr ? 0 : "");
/*
* One-time initialization. Generate the time-independent address that we
* will return if the match is successful. This address is also used as a
* matching template.
*/
if (time_indep_sender_buf == 0) {
time_indep_sender_buf = vstring_alloc(10);
vstring_strcpy(time_indep_sender_buf, var_verify_sender);
rewrite_clnt_internal(MAIL_ATTR_RWR_LOCAL, STR(time_indep_sender_buf),
time_indep_sender_buf);
}
/*
* Check the time-independent sender localpart.
*/
if ((my_at_domain = strchr(STR(time_indep_sender_buf), '@')) != 0)
base_len = my_at_domain - STR(time_indep_sender_buf);
else
base_len = LEN(time_indep_sender_buf);
if (strncasecmp_utf8(STR(time_indep_sender_buf), their_addr, base_len) != 0)
return (0); /* sender localpart mis-match */
/*
* Check the time-independent domain.
*/
if ((their_at_domain = strchr(their_addr, '@')) == 0 && my_at_domain != 0)
return (0); /* sender domain mis-match */
if (their_at_domain != 0
&& (my_at_domain == 0
|| strcasecmp_utf8(their_at_domain, my_at_domain) != 0))
return (0); /* sender domain mis-match */
/*
* Check the time-dependent portion.
*/
if (var_verify_sender_ttl > 0) {
their_epoch = safe_strtoul(their_addr + base_len, &cp, VERIFY_BASE);
if ((*cp != '@' && *cp != 0)
|| (their_epoch == ULONG_MAX && errno == ERANGE))
return (0); /* malformed time stamp */
my_epoch = VERIFY_SENDER_ADDR_EPOCH();
if (their_epoch < my_epoch - 1 || their_epoch > my_epoch + 1)
return (0); /* outside time window */
}
/*
* No time-dependent portion.
*/
else {
if (their_addr[base_len] != '@' && their_addr[base_len] != 0)
return (0); /* garbage after sender base */
}
return (STR(time_indep_sender_buf));
}
/*
* Proof-of-concept test program. Read test address_verify_sender and
* address_verify_sender_ttl values from stdin, and report results that we
* would get on stdout.
*/
#ifdef TEST
#include <stdlib.h>
#include <vstream.h>
#include <msg_vstream.h>
#include <vstring_vstream.h>
#include <mail_conf.h>
#include <conv_time.h>
int main(int argc, char **argv)
{
const char *verify_sender;
const char *valid_sender;
msg_vstream_init(argv[0], VSTREAM_ERR);
/*
* Prepare to talk to the address rewriting service.
*/
mail_conf_read();
vstream_printf("using config files in %s\n", var_config_dir);
if (chdir(var_queue_dir) < 0)
msg_fatal("chdir %s: %m", var_queue_dir);
/*
* Parse JCL.
*/
if (argc != 3)
msg_fatal("usage: %s address_verify_sender address_verify_sender_ttl",
argv[0]);
var_verify_sender = argv[1];
if (conv_time(argv[2], &var_verify_sender_ttl, 's') == 0)
msg_fatal("bad time value: %s", argv[2]);
verify_time = time((time_t *) 0);
/*
* Compute the current probe sender address.
*/
verify_sender = make_verify_sender_addr();
/*
* Check two past time slots.
*/
if (var_verify_sender_ttl > 0) {
verify_time -= 2 * var_verify_sender_ttl;
vstream_printf("\"%s\" matches prev2: \"%s\"\n", verify_sender,
(valid_sender = valid_verify_sender_addr(verify_sender)) != 0 ?
valid_sender : "nope");
verify_time += var_verify_sender_ttl;
vstream_printf("\"%s\" matches prev1: \"%s\"\n", verify_sender,
(valid_sender = valid_verify_sender_addr(verify_sender)) != 0 ?
valid_sender : "nope");
verify_time += var_verify_sender_ttl;
}
/*
* Check the current time slot.
*/
vstream_printf("\"%s\" matches self: \"%s\"\n", verify_sender,
(valid_sender = valid_verify_sender_addr(verify_sender)) != 0 ?
valid_sender : "nope");
/*
* Check two future time slots.
*/
if (var_verify_sender_ttl > 0) {
verify_time += var_verify_sender_ttl;
vstream_printf("\"%s\" matches next1: \"%s\"\n", verify_sender,
(valid_sender = valid_verify_sender_addr(verify_sender)) != 0 ?
valid_sender : "nope");
verify_time += var_verify_sender_ttl;
vstream_printf("\"%s\" matches next2: \"%s\"\n", verify_sender,
(valid_sender = valid_verify_sender_addr(verify_sender)) != 0 ?
valid_sender : "nope");
}
vstream_fflush(VSTREAM_OUT);
exit(0);
}
#endif