1 /*************************************************
2 * Exim - an Internet mail transport agent *
3 *************************************************/
5 /* Copyright (c) The Exim Maintainers 2020 - 2022 */
6 /* Copyright (c) University of Cambridge 1995 - 2018 */
7 /* See the file NOTICE for conditions of use and distribution. */
9 /* This module provides TLS (aka SSL) support for Exim. The code for OpenSSL is
10 based on a patch that was originally contributed by Steve Haslam. It was
11 adapted from stunnel, a GPL program by Michal Trojnara. The code for GNU TLS is
12 based on a patch contributed by Nikos Mavrogiannopoulos. Because these packages
13 are so very different, the functions for each are kept in separate files. The
14 relevant file is #included as required, after any any common functions.
16 No cryptographic code is included in Exim. All this module does is to call
17 functions from the OpenSSL or GNU TLS libraries. */
21 #include "transports/smtp.h"
23 #if !defined(DISABLE_TLS) && !defined(USE_OPENSSL) && !defined(USE_GNUTLS)
24 # error One of USE_OPENSSL or USE_GNUTLS must be defined for a TLS build
29 static void tls_client_resmption_key(tls_support *, smtp_connect_args *,
30 smtp_transport_options_block *);
33 #if defined(MACRO_PREDEF) && !defined(DISABLE_TLS)
34 # include "macro_predef.h"
38 # include "tls-openssl.c"
44 static void tls_per_lib_daemon_init(void);
45 static void tls_per_lib_daemon_tick(void);
46 static unsigned tls_server_creds_init(void);
47 static void tls_server_creds_invalidate(void);
48 static void tls_client_creds_init(transport_instance *, BOOL);
49 static void tls_client_creds_invalidate(transport_instance *);
50 static void tls_daemon_creds_reload(void);
51 static BOOL opt_set_and_noexpand(const uschar *);
52 static BOOL opt_unset_or_noexpand(const uschar *);
56 /* This module is compiled only when it is specifically requested in the
57 build-time configuration. However, some compilers don't like compiling empty
58 modules, so keep them happy with a dummy when skipping the rest. Make it
59 reference itself to stop picky compilers complaining that it is unused, and put
60 in a dummy argument to stop even pickier compilers complaining about infinite
64 static void dummy(int x) { dummy(x-1); }
65 #else /* most of the rest of the file */
67 const exim_tlslib_state null_tls_preload = {0};
69 /* Static variables that are used for buffering data by both sets of
70 functions and the common functions below.
72 We're moving away from this; GnuTLS is already using a state, which
73 can switch, so we can do TLS callouts during ACLs. */
75 static const int ssl_xfer_buffer_size = 4096;
77 static uschar *ssl_xfer_buffer = NULL;
78 static int ssl_xfer_buffer_lwm = 0;
79 static int ssl_xfer_buffer_hwm = 0;
80 static int ssl_xfer_eof = FALSE;
81 static BOOL ssl_xfer_error = FALSE;
84 #ifdef EXIM_HAVE_KEVENT
85 # define KEV_SIZE 16 /* Eight file,dir pairs */
86 static struct kevent kev[KEV_SIZE];
87 static int kev_used = 0;
90 static unsigned tls_creds_expire = 0;
92 /*************************************************
93 * Expand string; give error on failure *
94 *************************************************/
96 /* If expansion is forced to fail, set the result NULL and return TRUE.
97 Other failures return FALSE. For a server, an SMTP response is given.
100 s the string to expand; if NULL just return TRUE
101 name name of string being expanded (for error)
102 result where to put the result
104 Returns: TRUE if OK; result may still be NULL after forced failure
108 expand_check(const uschar *s, const uschar *name, uschar **result, uschar ** errstr)
112 else if ( !(*result = expand_string(US s)) /* need to clean up const more */
113 && !f.expand_string_forcedfail
116 *errstr = US"Internal error";
117 log_write(0, LOG_MAIN|LOG_PANIC, "expansion of %s failed: %s", name,
118 expand_string_message);
125 #if defined(EXIM_HAVE_INOTIFY) || defined(EXIM_HAVE_KEVENT)
126 /* Add the directory for a filename to the inotify handle, creating that if
127 needed. This is enough to see changes to files in that dir.
128 Return boolean success.
130 The word "system" fails, which is on the safe side as we don't know what
131 directory it implies nor if the TLS library handles a watch for us.
133 The string "system,cache" is recognised and explicitly accepted without
134 setting a watch. This permits the system CA bundle to be cached even though
135 we have no way to tell when it gets modified by an update.
136 The call chain for OpenSSL uses a (undocumented) call into the library
137 to discover the actual file. We don't know what GnuTLS uses.
139 A full set of caching including the CAs takes 35ms output off of the
140 server tls_init() (GnuTLS, Fedora 32, 2018-class x86_64 laptop hardware).
143 tls_set_one_watch(const uschar * filename)
144 # ifdef EXIM_HAVE_INOTIFY
146 uschar buf[PATH_MAX];
150 if (Ustrcmp(filename, "system,cache") == 0) return TRUE;
151 if (!(s = Ustrrchr(filename, '/'))) return FALSE;
153 for (unsigned loop = 20;
154 (len = readlink(CCS filename, CS buf, sizeof(buf))) >= 0; )
156 if (--loop == 0) { errno = ELOOP; return FALSE; }
157 filename = buf[0] == '/'
158 ? string_copyn(buf, (unsigned)len) /* mem released by tls_set_watch */
159 : string_sprintf("%.*s/%.*s", (int)(s - filename), (int)len);
160 s = Ustrrchr(filename, '/');
163 return FALSE; /* other error */
166 s = string_copyn(filename, s - filename); /* mem released by tls_set_watch */
168 DEBUG(D_tls) debug_printf("watch dir '%s'\n", s);
170 if (inotify_add_watch(tls_watch_fd, CCS s,
171 IN_ONESHOT | IN_CLOSE_WRITE | IN_DELETE | IN_DELETE_SELF
172 | IN_MOVED_FROM | IN_MOVED_TO | IN_MOVE_SELF) >= 0)
174 DEBUG(D_tls) debug_printf("notify_add_watch: %s\n", strerror(errno));
178 # ifdef EXIM_HAVE_KEVENT
181 int fd1, fd2, i, j, cnt = 0;
184 struct kevent k_dummy;
185 struct timespec ts = {0};
189 if (Ustrcmp(filename, "system,cache") == 0) return TRUE;
193 if (kev_used > KEV_SIZE-2) { s = US"out of kev space"; goto bad; }
194 if (!(s = Ustrrchr(filename, '/'))) return FALSE;
195 s = string_copyn(filename, s - filename); /* mem released by tls_set_watch */
197 /* The dir open will fail if there is a symlink on the path. Fine; it's too
198 much effort to handle all possible cases; just refuse the preload. */
200 if ((fd2 = open(CCS s, O_RDONLY | O_NOFOLLOW)) < 0) { s = US"open dir"; goto bad; }
202 if ((lstat(CCS filename, &sb)) < 0) { s = US"lstat"; goto bad; }
203 if (!S_ISLNK(sb.st_mode))
205 if ((fd1 = open(CCS filename, O_RDONLY | O_NOFOLLOW)) < 0)
206 { s = US"open file"; goto bad; }
207 DEBUG(D_tls) debug_printf("watch file '%s':\t%d\n", filename, fd1);
208 EV_SET(&kev[kev_used++],
211 EV_ADD | EV_ENABLE | EV_ONESHOT,
212 NOTE_DELETE | NOTE_WRITE | NOTE_EXTEND
213 | NOTE_ATTRIB | NOTE_RENAME | NOTE_REVOKE,
218 DEBUG(D_tls) debug_printf("watch dir '%s':\t%d\n", s, fd2);
219 EV_SET(&kev[kev_used++],
222 EV_ADD | EV_ENABLE | EV_ONESHOT,
223 NOTE_DELETE | NOTE_WRITE | NOTE_EXTEND
224 | NOTE_ATTRIB | NOTE_RENAME | NOTE_REVOKE,
229 if (!(S_ISLNK(sb.st_mode))) break;
231 t = store_get(1024, GET_UNTAINTED);
232 Ustrncpy(t, s, 1022);
235 if ((i = readlink(CCS filename, (void *)(t+j), 1023-j)) < 0) { s = US"readlink"; goto bad; }
238 store_release_above(t+1);
242 if (kevent(tls_watch_fd, &kev[kev_used-cnt], cnt, &k_dummy, 1, &ts) >= 0)
245 if (kevent(tls_watch_fd, &kev[kev_used-cnt], cnt, NULL, 0, NULL) >= 0)
253 debug_printf("%s: %s: %s\n", __FUNCTION__, s, strerror(errno));
255 debug_printf("%s: %s\n", __FUNCTION__, s);
258 # endif /*EXIM_HAVE_KEVENT*/
261 /* Create an inotify facility if needed.
262 Then set watches on the dir containing the given file or (optionally)
263 list of files. Return boolean success. */
266 tls_set_watch(const uschar * filename, BOOL list)
271 if (!filename || !*filename) return TRUE;
272 if (Ustrncmp(filename, "system", 6) == 0) return TRUE;
274 DEBUG(D_tls) debug_printf("tls_set_watch: '%s'\n", filename);
276 if ( tls_watch_fd < 0
277 # ifdef EXIM_HAVE_INOTIFY
278 && (tls_watch_fd = inotify_init1(O_CLOEXEC)) < 0
280 # ifdef EXIM_HAVE_KEVENT
281 && (tls_watch_fd = kqueue()) < 0
285 DEBUG(D_tls) debug_printf("inotify_init: %s\n", strerror(errno));
294 for (uschar * s; s = string_nextinlist(&filename, &sep, NULL, 0); )
295 if (!(rc = tls_set_one_watch(s))) break;
298 rc = tls_set_one_watch(filename);
301 if (!rc) DEBUG(D_tls) debug_printf("tls_set_watch() fail on '%s': %s\n", filename, strerror(errno));
307 tls_watch_discard_event(int fd)
309 #ifdef EXIM_HAVE_INOTIFY
310 (void) read(fd, big_buffer, big_buffer_size);
312 #ifdef EXIM_HAVE_KEVENT
314 struct timespec t = {0};
315 (void) kevent(fd, NULL, 0, &kev, 1, &t);
318 #endif /*EXIM_HAVE_INOTIFY*/
322 tls_client_creds_reload(BOOL watch)
324 for(transport_instance * t = transports; t; t = t->next)
325 if (Ustrcmp(t->driver_name, "smtp") == 0)
327 tls_client_creds_invalidate(t);
328 tls_client_creds_init(t, watch);
334 tls_watch_invalidate(void)
336 if (tls_watch_fd < 0) return;
338 #ifdef EXIM_HAVE_KEVENT
339 /* Close the files we had open for kevent */
340 for (int i = 0; i < kev_used; i++)
342 DEBUG(D_tls) debug_printf("closing watch fd: %d\n", (int) kev[i].ident);
343 (void) close((int) kev[i].ident);
344 kev[i].ident = (uintptr_t)-1;
355 tls_daemon_creds_reload(void)
359 #ifdef EXIM_HAVE_KEVENT
360 tls_watch_invalidate();
363 tls_server_creds_invalidate();
364 tls_creds_expire = (lifetime = tls_server_creds_init())
365 ? time(NULL) + lifetime : 0;
367 tls_client_creds_reload(TRUE);
371 /* Utility predicates for use by the per-library code */
373 opt_set_and_noexpand(const uschar * opt)
374 { return opt && *opt && Ustrchr(opt, '$') == NULL; }
377 opt_unset_or_noexpand(const uschar * opt)
378 { return !opt || Ustrchr(opt, '$') == NULL; }
382 /* Called every time round the daemon loop.
384 If we reloaded fd-watcher, return the old watch fd
385 having modified the global for the new one. Otherwise
390 tls_daemon_tick(void)
392 int old_watch_fd = tls_watch_fd;
394 tls_per_lib_daemon_tick();
395 #if defined(EXIM_HAVE_INOTIFY) || defined(EXIM_HAVE_KEVENT)
396 if (tls_creds_expire && time(NULL) >= tls_creds_expire)
398 /* The server cert is a selfsign, with limited lifetime. Dump it and
399 generate a new one. Reload the rest of the creds also as the machinery
402 DEBUG(D_tls) debug_printf("selfsign cert rotate\n");
403 tls_creds_expire = 0;
404 tls_daemon_creds_reload();
407 else if (tls_watch_trigger_time && time(NULL) >= tls_watch_trigger_time + 5)
409 /* Called, after a delay for multiple file ops to get done, from
410 the daemon when any of the watches added (above) fire.
411 Dump the set of watches and arrange to reload cached creds (which
412 will set up new watches). */
414 DEBUG(D_tls) debug_printf("watch triggered\n");
415 tls_watch_trigger_time = tls_creds_expire = 0;
416 tls_daemon_creds_reload();
423 /* Called once at daemon startup */
426 tls_daemon_init(void)
428 tls_per_lib_daemon_init();
432 /*************************************************
433 * Timezone environment flipping *
434 *************************************************/
439 uschar * old = US getenv("TZ");
440 (void) setenv("TZ", CCS tz, 1);
446 restore_tz(uschar * tz)
449 (void) setenv("TZ", CCS tz, 1);
451 (void) os_unsetenv(US"TZ");
455 /*************************************************
456 * Many functions are package-specific *
457 *************************************************/
460 # include "tls-gnu.c"
461 # include "tlscert-gnu.c"
462 # define ssl_xfer_buffer (state_server.xfer_buffer)
463 # define ssl_xfer_buffer_lwm (state_server.xfer_buffer_lwm)
464 # define ssl_xfer_buffer_hwm (state_server.xfer_buffer_hwm)
465 # define ssl_xfer_eof (state_server.xfer_eof)
466 # define ssl_xfer_error (state_server.xfer_error)
470 # include "tls-openssl.c"
471 # include "tlscert-openssl.c"
476 /*************************************************
477 * TLS version of ungetc *
478 *************************************************/
480 /* Puts a character back in the input buffer. Only ever
482 Only used by the server-side TLS.
487 Returns: the character
493 if (ssl_xfer_buffer_lwm <= 0)
494 log_write(0, LOG_MAIN|LOG_PANIC_DIE, "buffer underflow in tls_ungetc");
496 ssl_xfer_buffer[--ssl_xfer_buffer_lwm] = ch;
502 /*************************************************
503 * TLS version of feof *
504 *************************************************/
506 /* Tests for a previous EOF
507 Only used by the server-side TLS.
510 Returns: non-zero if the eof flag is set
516 return (int)ssl_xfer_eof;
521 /*************************************************
522 * TLS version of ferror *
523 *************************************************/
525 /* Tests for a previous read error, and returns with errno
526 restored to what it was when the error was detected.
527 Only used by the server-side TLS.
529 >>>>> Hmm. Errno not handled yet. Where do we get it from? >>>>>
532 Returns: non-zero if the error flag is set
538 return (int)ssl_xfer_error;
542 /*************************************************
543 * TLS version of smtp_buffered *
544 *************************************************/
546 /* Tests for unused chars in the TLS input buffer.
547 Only used by the server-side TLS.
554 tls_smtp_buffered(void)
556 return ssl_xfer_buffer_lwm < ssl_xfer_buffer_hwm;
560 #endif /*DISABLE_TLS*/
563 tls_modify_variables(tls_support * dest_tsp)
565 modify_variable(US"tls_bits", &dest_tsp->bits);
566 modify_variable(US"tls_certificate_verified", &dest_tsp->certificate_verified);
567 modify_variable(US"tls_cipher", &dest_tsp->cipher);
568 modify_variable(US"tls_peerdn", &dest_tsp->peerdn);
570 modify_variable(US"tls_sni", &dest_tsp->sni);
576 /************************************************
577 * TLS certificate name operations *
578 ************************************************/
580 /* Convert an rfc4514 DN to an exim comma-sep list.
581 Backslashed commas need to be replaced by doublecomma
582 for Exim's list quoting. We modify the given string
587 dn_to_list(uschar * dn)
589 for (uschar * cp = dn; *cp; cp++)
590 if (cp[0] == '\\' && cp[1] == ',')
595 /* Extract fields of a given type from an RFC4514-
596 format Distinguished Name. Return an Exim list.
597 NOTE: We modify the supplied dn string during operation.
600 dn Distinguished Name string
601 mod list containing optional output list-sep and
602 field selector match, comma-separated
604 allocated string with list of matching fields,
609 tls_field_from_dn(uschar * dn, const uschar * mod)
612 uschar outsep = '\n';
614 uschar * match = NULL;
616 gstring * list = NULL;
618 while ((ele = string_nextinlist(&mod, &insep, NULL, 0)))
620 match = ele; /* field tag to match */
622 outsep = ele[1]; /* nondefault output separator */
626 len = match ? Ustrlen(match) : -1;
627 while ((ele = string_nextinlist(CUSS &dn, &insep, NULL, 0)))
629 || Ustrncmp(ele, match, len) == 0 && ele[len] == '='
631 list = string_append_listele(list, outsep, ele+len+1);
632 return string_from_gstring(list);
636 /* Compare a domain name with a possibly-wildcarded name. Wildcards
637 are restricted to a single one, as the first element of patterns
638 having at least three dot-separated elements. Case-independent.
639 Return TRUE for a match
642 is_name_match(const uschar * name, const uschar * pat)
645 return *pat == '*' /* possible wildcard match */
646 ? *++pat == '.' /* starts star, dot */
647 && !Ustrchr(++pat, '*') /* has no more stars */
648 && Ustrchr(pat, '.') /* and has another dot. */
649 && (cp = Ustrchr(name, '.'))/* The name has at least one dot */
650 && strcmpic(++cp, pat) == 0 /* and we only compare after it. */
651 : !Ustrchr(pat+1, '*')
652 && strcmpic(name, pat) == 0;
655 /* Compare a list of names with the dnsname elements
656 of the Subject Alternate Name, if any, and the
660 namelist names to compare
668 tls_is_name_for_cert(const uschar * namelist, void * cert)
670 uschar * altnames = tls_cert_subject_altname(cert, US"dns");
676 if ((altnames = tls_cert_subject_altname(cert, US"dns")))
679 while ((cmpname = string_nextinlist(&namelist, &cmp_sep, NULL, 0)))
681 const uschar * an = altnames;
682 while ((certname = string_nextinlist(&an, &alt_sep, NULL, 0)))
683 if (is_name_match(cmpname, certname))
688 else if ((subjdn = tls_cert_subject(cert, NULL)))
693 while ((cmpname = string_nextinlist(&namelist, &cmp_sep, NULL, 0)))
695 const uschar * sn = subjdn;
696 while ((certname = string_nextinlist(&sn, &sn_sep, NULL, 0)))
697 if ( *certname++ == 'C'
698 && *certname++ == 'N'
699 && *certname++ == '='
700 && is_name_match(cmpname, certname)
708 /* Environment cleanup: The GnuTLS library uses SSLKEYLOGFILE in the environment
709 and writes a file by that name. Our OpenSSL code does the same, using keying
710 info from the library API.
711 The GnuTLS support only works if exim is run by root, not taking advantage of
713 You can use either the external environment (modulo the keep_environment config)
714 or the add_environment config option for SSLKEYLOGFILE; the latter takes
717 If the path is absolute, require it starts with the spooldir; otherwise delete
718 the env variable. If relative, prefix the spooldir.
723 uschar * path = US getenv("SSLKEYLOGFILE");
726 unsetenv("SSLKEYLOGFILE");
727 else if (*path != '/')
730 debug_printf("prepending spooldir to env SSLKEYLOGFILE\n");
731 setenv("SSLKEYLOGFILE", CCS string_sprintf("%s/%s", spool_directory, path), 1);
733 else if (Ustrncmp(path, spool_directory, Ustrlen(spool_directory)) != 0)
736 debug_printf("removing env SSLKEYLOGFILE=%s: not under spooldir\n", path);
737 unsetenv("SSLKEYLOGFILE");
741 /*************************************************
742 * Drop privs for checking TLS config *
743 *************************************************/
745 /* We want to validate TLS options during readconf, but do not want to be
746 root when we call into the TLS library, in case of library linkage errors
747 which cause segfaults; before this check, those were always done as the Exim
748 runtime user and it makes sense to continue with that.
750 Assumes: tls_require_ciphers has been set, if it will be
751 exim_user has been set, if it will be
752 exim_group has been set, if it will be
754 Returns: bool for "okay"; false will cause caller to immediately exit.
758 tls_dropprivs_validate_require_cipher(BOOL nowarn)
760 const uschar *errmsg;
763 void (*oldsignal)(int);
765 /* If TLS will never be used, no point checking ciphers */
767 if ( !tls_advertise_hosts
768 || !*tls_advertise_hosts
769 || Ustrcmp(tls_advertise_hosts, ":") == 0
772 else if (!nowarn && !tls_certificate)
773 log_write(0, LOG_MAIN,
774 "Warning: No server certificate defined; will use a selfsigned one.\n"
775 " Suggested action: either install a certificate or change tls_advertise_hosts option");
777 oldsignal = signal(SIGCHLD, SIG_DFL);
780 if ((pid = exim_fork(US"cipher-validate")) < 0)
781 log_write(0, LOG_MAIN|LOG_PANIC_DIE, "fork failed for TLS check");
785 /* in some modes, will have dropped privilege already */
787 exim_setugid(exim_uid, exim_gid, FALSE,
788 US"calling tls_validate_require_cipher");
790 if ((errmsg = tls_validate_require_cipher()))
791 log_write(0, LOG_PANIC_DIE|LOG_CONFIG,
792 "tls_require_ciphers invalid: %s", errmsg);
794 exim_underbar_exit(EXIT_SUCCESS);
798 rc = waitpid(pid, &status, 0);
799 } while (rc < 0 && errno == EINTR);
802 debug_printf("tls_validate_require_cipher child %d ended: status=0x%x\n",
805 signal(SIGCHLD, oldsignal);
814 tls_client_resmption_key(tls_support * tlsp, smtp_connect_args * conn_args,
815 smtp_transport_options_block * ob)
817 #ifndef DISABLE_TLS_RESUME
818 hctx * h = &tlsp->resume_hctx;
822 DEBUG(D_tls) if (conn_args->host_lbserver)
823 debug_printf("TLS: lbserver '%s'\n", conn_args->host_lbserver);
825 # ifdef EXIM_HAVE_SHA2
826 exim_sha_init(h, HASH_SHA2_256);
828 exim_sha_init(h, HASH_SHA1);
830 exim_sha_update_string(h, conn_args->host_lbserver);
833 exim_sha_update(h, CUS &conn_args->tlsa_dnsa, sizeof(dns_answer));
835 exim_sha_update_string(h, conn_args->host->address);
836 exim_sha_update(h, CUS &conn_args->host->port, sizeof(conn_args->host->port));
837 exim_sha_update_string(h, conn_args->sending_ip_address);
838 exim_sha_update_string(h, openssl_options);
839 exim_sha_update_string(h, ob->tls_require_ciphers);
840 exim_sha_update_string(h, tlsp->sni);
841 # ifdef EXIM_HAVE_ALPN
842 exim_sha_update_string(h, ob->tls_alpn);
844 exim_sha_finish(h, &b);
845 for (g = string_get(b.len*2+1); b.len-- > 0; )
846 g = string_fmt_append(g, "%02x", *b.data++);
847 tlsp->resume_index = string_from_gstring(g);
848 DEBUG(D_tls) debug_printf("TLS: resume session index %s\n", tlsp->resume_index);
852 #endif /*!DISABLE_TLS*/
853 #endif /*!MACRO_PREDEF*/