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. */
8 /* SPDX-License-Identifier: GPL-2.0-or-later */
10 /* This module provides TLS (aka SSL) support for Exim. The code for OpenSSL is
11 based on a patch that was originally contributed by Steve Haslam. It was
12 adapted from stunnel, a GPL program by Michal Trojnara. The code for GNU TLS is
13 based on a patch contributed by Nikos Mavrogiannopoulos. Because these packages
14 are so very different, the functions for each are kept in separate files. The
15 relevant file is #included as required, after any any common functions.
17 No cryptographic code is included in Exim. All this module does is to call
18 functions from the OpenSSL or GNU TLS libraries. */
22 #include "transports/smtp.h"
24 #if !defined(DISABLE_TLS) && !defined(USE_OPENSSL) && !defined(USE_GNUTLS)
25 # error One of USE_OPENSSL or USE_GNUTLS must be defined for a TLS build
29 #if defined(MACRO_PREDEF) && !defined(DISABLE_TLS)
30 # include "macro_predef.h"
34 # include "tls-openssl.c"
40 static void tls_per_lib_daemon_init(void);
41 static void tls_per_lib_daemon_tick(void);
42 static unsigned tls_server_creds_init(void);
43 static void tls_server_creds_invalidate(void);
44 static void tls_client_creds_init(transport_instance *, BOOL);
45 static void tls_client_creds_invalidate(transport_instance *);
46 static void tls_daemon_creds_reload(void);
47 static BOOL opt_set_and_noexpand(const uschar *);
48 static BOOL opt_unset_or_noexpand(const uschar *);
52 /* This module is compiled only when it is specifically requested in the
53 build-time configuration. However, some compilers don't like compiling empty
54 modules, so keep them happy with a dummy when skipping the rest. Make it
55 reference itself to stop picky compilers complaining that it is unused, and put
56 in a dummy argument to stop even pickier compilers complaining about infinite
60 static void dummy(int x) { dummy(x-1); }
61 #else /* most of the rest of the file */
63 const exim_tlslib_state null_tls_preload = {0};
65 /* Static variables that are used for buffering data by both sets of
66 functions and the common functions below.
68 We're moving away from this; GnuTLS is already using a state, which
69 can switch, so we can do TLS callouts during ACLs. */
71 static const int ssl_xfer_buffer_size = 4096;
73 static uschar *ssl_xfer_buffer = NULL;
74 static int ssl_xfer_buffer_lwm = 0;
75 static int ssl_xfer_buffer_hwm = 0;
76 static int ssl_xfer_eof = FALSE;
77 static BOOL ssl_xfer_error = FALSE;
80 #ifdef EXIM_HAVE_KEVENT
81 # define KEV_SIZE 16 /* Eight file,dir pairs */
82 static struct kevent kev[KEV_SIZE];
83 static int kev_used = 0;
86 static unsigned tls_creds_expire = 0;
88 /*************************************************
89 * Expand string; give error on failure *
90 *************************************************/
92 /* If expansion is forced to fail, set the result NULL and return TRUE.
93 Other failures return FALSE. For a server, an SMTP response is given.
96 s the string to expand; if NULL just return TRUE
97 name name of string being expanded (for error)
98 result where to put the result
100 Returns: TRUE if OK; result may still be NULL after forced failure
104 expand_check(const uschar * s, const uschar * name,
105 uschar ** result, uschar ** errstr)
109 else if ( !(*result = expand_string(US s)) /* need to clean up const more */
110 && !f.expand_string_forcedfail
113 *errstr = US"Internal error";
114 log_write(0, LOG_MAIN|LOG_PANIC, "expansion of %s failed: %s", name,
115 expand_string_message);
122 #if defined(EXIM_HAVE_INOTIFY) || defined(EXIM_HAVE_KEVENT)
123 /* Add the directory for a filename to the inotify handle, creating that if
124 needed. This is enough to see changes to files in that dir.
125 Return boolean success.
127 The word "system" fails, which is on the safe side as we don't know what
128 directory it implies nor if the TLS library handles a watch for us.
130 The string "system,cache" is recognised and explicitly accepted without
131 setting a watch. This permits the system CA bundle to be cached even though
132 we have no way to tell when it gets modified by an update.
133 The call chain for OpenSSL uses a (undocumented) call into the library
134 to discover the actual file. We don't know what GnuTLS uses.
136 A full set of caching including the CAs takes 35ms output off of the
137 server tls_init() (GnuTLS, Fedora 32, 2018-class x86_64 laptop hardware).
140 tls_set_one_watch(const uschar * filename)
141 # ifdef EXIM_HAVE_INOTIFY
143 uschar buf[PATH_MAX];
147 if (Ustrcmp(filename, "system,cache") == 0) return TRUE;
148 if (!(s = Ustrrchr(filename, '/'))) return FALSE;
150 for (unsigned loop = 20;
151 (len = readlink(CCS filename, CS buf, sizeof(buf))) >= 0; )
153 if (--loop == 0) { errno = ELOOP; return FALSE; }
154 filename = buf[0] == '/'
155 ? string_copyn(buf, (unsigned)len) /* mem released by tls_set_watch */
156 : string_sprintf("%.*s/%.*s", (int)(s - filename), filename, (int)len, buf);
157 s = Ustrrchr(filename, '/');
160 return FALSE; /* other error */
163 s = string_copyn(filename, s - filename); /* mem released by tls_set_watch */
165 DEBUG(D_tls) debug_printf("watch dir '%s'\n", s);
167 if (inotify_add_watch(tls_watch_fd, CCS s,
168 IN_ONESHOT | IN_CLOSE_WRITE | IN_DELETE | IN_DELETE_SELF
169 | IN_MOVED_FROM | IN_MOVED_TO | IN_MOVE_SELF) >= 0)
171 DEBUG(D_tls) debug_printf("notify_add_watch: %s\n", strerror(errno));
175 # ifdef EXIM_HAVE_KEVENT
178 int fd1, fd2, i, j, cnt = 0;
181 struct kevent k_dummy;
182 struct timespec ts = {0};
186 if (Ustrcmp(filename, "system,cache") == 0) return TRUE;
190 if (kev_used > KEV_SIZE-2) { s = US"out of kev space"; goto bad; }
191 if (!(s = Ustrrchr(filename, '/'))) return FALSE;
192 s = string_copyn(filename, s - filename); /* mem released by tls_set_watch */
194 /* The dir open will fail if there is a symlink on the path. Fine; it's too
195 much effort to handle all possible cases; just refuse the preload. */
197 if ((fd2 = open(CCS s, O_RDONLY | O_NOFOLLOW)) < 0) { s = US"open dir"; goto bad; }
199 if ((lstat(CCS filename, &sb)) < 0) { s = US"lstat"; goto bad; }
200 if (!S_ISLNK(sb.st_mode))
202 if ((fd1 = open(CCS filename, O_RDONLY | O_NOFOLLOW)) < 0)
203 { s = US"open file"; goto bad; }
204 DEBUG(D_tls) debug_printf("watch file '%s':\t%d\n", filename, fd1);
205 EV_SET(&kev[kev_used++],
208 EV_ADD | EV_ENABLE | EV_ONESHOT,
209 NOTE_DELETE | NOTE_WRITE | NOTE_EXTEND
210 | NOTE_ATTRIB | NOTE_RENAME | NOTE_REVOKE,
215 DEBUG(D_tls) debug_printf("watch dir '%s':\t%d\n", s, fd2);
216 EV_SET(&kev[kev_used++],
219 EV_ADD | EV_ENABLE | EV_ONESHOT,
220 NOTE_DELETE | NOTE_WRITE | NOTE_EXTEND
221 | NOTE_ATTRIB | NOTE_RENAME | NOTE_REVOKE,
226 if (!(S_ISLNK(sb.st_mode))) break;
228 t = store_get(1024, GET_UNTAINTED);
229 Ustrncpy(t, s, 1022);
232 if ((i = readlink(CCS filename, (void *)(t+j), 1023-j)) < 0) { s = US"readlink"; goto bad; }
235 store_release_above(t+1);
239 if (kevent(tls_watch_fd, &kev[kev_used-cnt], cnt, &k_dummy, 1, &ts) >= 0)
242 if (kevent(tls_watch_fd, &kev[kev_used-cnt], cnt, NULL, 0, NULL) >= 0)
250 debug_printf("%s: %s: %s\n", __FUNCTION__, s, strerror(errno));
252 debug_printf("%s: %s\n", __FUNCTION__, s);
255 # endif /*EXIM_HAVE_KEVENT*/
258 /* Create an inotify facility if needed.
259 Then set watches on the dir containing the given file or (optionally)
260 list of files. Return boolean success. */
263 tls_set_watch(const uschar * filename, BOOL list)
268 if (!filename || !*filename) return TRUE;
269 if (Ustrncmp(filename, "system", 6) == 0) return TRUE;
271 DEBUG(D_tls) debug_printf("tls_set_watch: '%s'\n", filename);
273 if ( tls_watch_fd < 0
274 # ifdef EXIM_HAVE_INOTIFY
275 && (tls_watch_fd = inotify_init1(O_CLOEXEC)) < 0
277 # ifdef EXIM_HAVE_KEVENT
278 && (tls_watch_fd = kqueue()) < 0
282 DEBUG(D_tls) debug_printf("inotify_init: %s\n", strerror(errno));
291 for (uschar * s; s = string_nextinlist(&filename, &sep, NULL, 0); )
292 if (!(rc = tls_set_one_watch(s))) break;
295 rc = tls_set_one_watch(filename);
298 if (!rc) DEBUG(D_tls) debug_printf("tls_set_watch() fail on '%s': %s\n", filename, strerror(errno));
304 tls_watch_discard_event(int fd)
306 #ifdef EXIM_HAVE_INOTIFY
307 (void) read(fd, big_buffer, big_buffer_size);
309 #ifdef EXIM_HAVE_KEVENT
311 struct timespec t = {0};
312 (void) kevent(fd, NULL, 0, &kev, 1, &t);
315 #endif /*EXIM_HAVE_INOTIFY*/
319 tls_client_creds_reload(BOOL watch)
321 for(transport_instance * t = transports; t; t = t->next)
322 if (Ustrcmp(t->driver_name, "smtp") == 0)
324 tls_client_creds_invalidate(t);
325 tls_client_creds_init(t, watch);
331 tls_watch_invalidate(void)
333 if (tls_watch_fd < 0) return;
335 #ifdef EXIM_HAVE_KEVENT
336 /* Close the files we had open for kevent */
337 for (int i = 0; i < kev_used; i++)
339 DEBUG(D_tls) debug_printf("closing watch fd: %d\n", (int) kev[i].ident);
340 (void) close((int) kev[i].ident);
341 kev[i].ident = (uintptr_t)-1;
352 tls_daemon_creds_reload(void)
356 #ifdef EXIM_HAVE_KEVENT
357 tls_watch_invalidate();
360 tls_server_creds_invalidate();
362 /* _expire is for a time-limited selfsign server cert */
363 tls_creds_expire = (lifetime = tls_server_creds_init())
364 ? time(NULL) + lifetime : 0;
366 tls_client_creds_reload(TRUE);
370 /* Utility predicates for use by the per-library code */
372 opt_set_and_noexpand(const uschar * opt)
373 { return opt && *opt && Ustrchr(opt, '$') == NULL; }
376 opt_unset_or_noexpand(const uschar * opt)
377 { return !opt || Ustrchr(opt, '$') == NULL; }
381 /* Called every time round the daemon loop.
383 If we reloaded fd-watcher, return the old watch fd
384 having modified the global for the new one. Otherwise
389 tls_daemon_tick(void)
391 int old_watch_fd = tls_watch_fd;
393 tls_per_lib_daemon_tick();
394 #if defined(EXIM_HAVE_INOTIFY) || defined(EXIM_HAVE_KEVENT)
395 if (tls_creds_expire && time(NULL) >= tls_creds_expire)
397 /* The server cert is a selfsign, with limited lifetime. Dump it and
398 generate a new one. Reload the rest of the creds also as the machinery
401 DEBUG(D_tls) debug_printf("selfsign cert rotate\n");
402 tls_creds_expire = 0;
403 tls_daemon_creds_reload();
406 else if (tls_watch_trigger_time && time(NULL) >= tls_watch_trigger_time + 5)
408 /* Called, after a delay for multiple file ops to get done, from
409 the daemon when any of the watches added (above) fire.
410 Dump the set of watches and arrange to reload cached creds (which
411 will set up new watches). */
413 DEBUG(D_tls) debug_printf("watch triggered\n");
414 tls_watch_trigger_time = tls_creds_expire = 0;
415 tls_daemon_creds_reload();
422 /* Called once at daemon startup */
425 tls_daemon_init(void)
427 tls_per_lib_daemon_init();
431 /*************************************************
432 * Timezone environment flipping *
433 *************************************************/
438 uschar * old = US getenv("TZ");
439 (void) setenv("TZ", CCS tz, 1);
445 restore_tz(uschar * tz)
448 (void) setenv("TZ", CCS tz, 1);
450 (void) os_unsetenv(US"TZ");
454 /*************************************************
455 * Many functions are package-specific *
456 *************************************************/
458 static void tls_client_resmption_key(tls_support *, smtp_connect_args *,
459 smtp_transport_options_block *);
463 # include "tls-gnu.c"
464 # include "tlscert-gnu.c"
465 # define ssl_xfer_buffer (state_server.xfer_buffer)
466 # define ssl_xfer_buffer_lwm (state_server.xfer_buffer_lwm)
467 # define ssl_xfer_buffer_hwm (state_server.xfer_buffer_hwm)
468 # define ssl_xfer_eof (state_server.xfer_eof)
469 # define ssl_xfer_error (state_server.xfer_error)
473 # include "tls-openssl.c"
474 # include "tlscert-openssl.c"
479 /*************************************************
480 * TLS version of ungetc *
481 *************************************************/
483 /* Puts a character back in the input buffer. Only ever
485 Only used by the server-side TLS.
490 Returns: the character
496 if (ssl_xfer_buffer_lwm <= 0)
497 log_write(0, LOG_MAIN|LOG_PANIC_DIE, "buffer underflow in tls_ungetc");
499 ssl_xfer_buffer[--ssl_xfer_buffer_lwm] = ch;
505 /*************************************************
506 * TLS version of feof *
507 *************************************************/
509 /* Tests for a previous EOF
510 Only used by the server-side TLS.
513 Returns: non-zero if the eof flag is set
519 return (int)ssl_xfer_eof;
524 /*************************************************
525 * TLS version of ferror *
526 *************************************************/
528 /* Tests for a previous read error, and returns with errno
529 restored to what it was when the error was detected.
530 Only used by the server-side TLS.
532 >>>>> Hmm. Errno not handled yet. Where do we get it from? >>>>>
535 Returns: non-zero if the error flag is set
541 return (int)ssl_xfer_error;
545 /*************************************************
546 * TLS version of smtp_buffered *
547 *************************************************/
549 /* Tests for unused chars in the TLS input buffer.
550 Only used by the server-side TLS.
557 tls_smtp_buffered(void)
559 return ssl_xfer_buffer_lwm < ssl_xfer_buffer_hwm;
563 #endif /*DISABLE_TLS*/
566 tls_modify_variables(tls_support * dest_tsp)
568 modify_variable(US"tls_bits", &dest_tsp->bits);
569 modify_variable(US"tls_certificate_verified", &dest_tsp->certificate_verified);
570 modify_variable(US"tls_cipher", &dest_tsp->cipher);
571 modify_variable(US"tls_peerdn", &dest_tsp->peerdn);
573 modify_variable(US"tls_sni", &dest_tsp->sni);
579 /************************************************
580 * TLS certificate name operations *
581 ************************************************/
583 /* Convert an rfc4514 DN to an exim comma-sep list.
584 Backslashed commas need to be replaced by doublecomma
585 for Exim's list quoting. We modify the given string
590 dn_to_list(uschar * dn)
592 for (uschar * cp = dn; *cp; cp++)
593 if (cp[0] == '\\' && cp[1] == ',')
598 /* Extract fields of a given type from an RFC4514-
599 format Distinguished Name. Return an Exim list.
600 NOTE: We modify the supplied dn string during operation.
603 dn Distinguished Name string
604 mod list containing optional output list-sep and
605 field selector match, comma-separated
607 allocated string with list of matching fields,
612 tls_field_from_dn(uschar * dn, const uschar * mod)
615 uschar outsep = '\n';
617 uschar * match = NULL;
619 gstring * list = NULL;
621 while ((ele = string_nextinlist(&mod, &insep, NULL, 0)))
623 match = ele; /* field tag to match */
625 outsep = ele[1]; /* nondefault output separator */
629 len = match ? Ustrlen(match) : -1;
630 while ((ele = string_nextinlist(CUSS &dn, &insep, NULL, 0)))
632 || Ustrncmp(ele, match, len) == 0 && ele[len] == '='
634 list = string_append_listele(list, outsep, ele+len+1);
635 return string_from_gstring(list);
639 /* Compare a domain name with a possibly-wildcarded name. Wildcards
640 are restricted to a single one, as the first element of patterns
641 having at least three dot-separated elements. Case-independent.
642 Return TRUE for a match
645 is_name_match(const uschar * name, const uschar * pat)
648 return *pat == '*' /* possible wildcard match */
649 ? *++pat == '.' /* starts star, dot */
650 && !Ustrchr(++pat, '*') /* has no more stars */
651 && Ustrchr(pat, '.') /* and has another dot. */
652 && (cp = Ustrchr(name, '.'))/* The name has at least one dot */
653 && strcmpic(++cp, pat) == 0 /* and we only compare after it. */
654 : !Ustrchr(pat+1, '*')
655 && strcmpic(name, pat) == 0;
658 /* Compare a list of names with the dnsname elements
659 of the Subject Alternate Name, if any, and the
663 namelist names to compare
671 tls_is_name_for_cert(const uschar * namelist, void * cert)
673 uschar * altnames = tls_cert_subject_altname(cert, US"dns");
679 if ((altnames = tls_cert_subject_altname(cert, US"dns")))
682 while ((cmpname = string_nextinlist(&namelist, &cmp_sep, NULL, 0)))
684 const uschar * an = altnames;
685 while ((certname = string_nextinlist(&an, &alt_sep, NULL, 0)))
686 if (is_name_match(cmpname, certname))
691 else if ((subjdn = tls_cert_subject(cert, NULL)))
696 while ((cmpname = string_nextinlist(&namelist, &cmp_sep, NULL, 0)))
698 const uschar * sn = subjdn;
699 while ((certname = string_nextinlist(&sn, &sn_sep, NULL, 0)))
700 if ( *certname++ == 'C'
701 && *certname++ == 'N'
702 && *certname++ == '='
703 && is_name_match(cmpname, certname)
711 /* Environment cleanup: The GnuTLS library uses SSLKEYLOGFILE in the environment
712 and writes a file by that name. Our OpenSSL code does the same, using keying
713 info from the library API.
714 The GnuTLS support only works if exim is run by root, not taking advantage of
716 You can use either the external environment (modulo the keep_environment config)
717 or the add_environment config option for SSLKEYLOGFILE; the latter takes
720 If the path is absolute, require it starts with the spooldir; otherwise delete
721 the env variable. If relative, prefix the spooldir.
726 uschar * path = US getenv("SSLKEYLOGFILE");
729 unsetenv("SSLKEYLOGFILE");
730 else if (*path != '/')
733 debug_printf("prepending spooldir to env SSLKEYLOGFILE\n");
734 setenv("SSLKEYLOGFILE", CCS string_sprintf("%s/%s", spool_directory, path), 1);
736 else if (Ustrncmp(path, spool_directory, Ustrlen(spool_directory)) != 0)
739 debug_printf("removing env SSLKEYLOGFILE=%s: not under spooldir\n", path);
740 unsetenv("SSLKEYLOGFILE");
744 /*************************************************
745 * Drop privs for checking TLS config *
746 *************************************************/
748 /* We want to validate TLS options during readconf, but do not want to be
749 root when we call into the TLS library, in case of library linkage errors
750 which cause segfaults; before this check, those were always done as the Exim
751 runtime user and it makes sense to continue with that.
753 Assumes: tls_require_ciphers has been set, if it will be
754 exim_user has been set, if it will be
755 exim_group has been set, if it will be
757 Returns: bool for "okay"; false will cause caller to immediately exit.
761 tls_dropprivs_validate_require_cipher(BOOL nowarn)
763 const uschar *errmsg;
766 void (*oldsignal)(int);
768 /* If TLS will never be used, no point checking ciphers */
770 if ( !tls_advertise_hosts
771 || !*tls_advertise_hosts
772 || Ustrcmp(tls_advertise_hosts, ":") == 0
775 else if (!nowarn && !tls_certificate)
776 log_write(0, LOG_MAIN,
777 "Warning: No server certificate defined; will use a selfsigned one.\n"
778 " Suggested action: either install a certificate or change tls_advertise_hosts option");
780 oldsignal = signal(SIGCHLD, SIG_DFL);
783 if ((pid = exim_fork(US"cipher-validate")) < 0)
784 log_write(0, LOG_MAIN|LOG_PANIC_DIE, "fork failed for TLS check");
788 /* in some modes, will have dropped privilege already */
790 exim_setugid(exim_uid, exim_gid, FALSE,
791 US"calling tls_validate_require_cipher");
793 if ((errmsg = tls_validate_require_cipher()))
794 log_write(0, LOG_PANIC_DIE|LOG_CONFIG,
795 "tls_require_ciphers invalid: %s", errmsg);
797 exim_underbar_exit(EXIT_SUCCESS);
801 rc = waitpid(pid, &status, 0);
802 } while (rc < 0 && errno == EINTR);
805 debug_printf("tls_validate_require_cipher child %d ended: status=0x%x\n",
808 signal(SIGCHLD, oldsignal);
817 tls_client_resmption_key(tls_support * tlsp, smtp_connect_args * conn_args,
818 smtp_transport_options_block * ob)
820 #ifndef DISABLE_TLS_RESUME
821 hctx * h = &tlsp->resume_hctx;
825 DEBUG(D_tls) if (conn_args->host_lbserver)
826 debug_printf("TLS: lbserver '%s'\n", conn_args->host_lbserver);
828 # ifdef EXIM_HAVE_SHA2
829 exim_sha_init(h, HASH_SHA2_256);
831 exim_sha_init(h, HASH_SHA1);
833 exim_sha_update_string(h, conn_args->host_lbserver);
836 exim_sha_update(h, CUS &conn_args->tlsa_dnsa, sizeof(dns_answer));
838 exim_sha_update_string(h, conn_args->host->address);
839 exim_sha_update(h, CUS &conn_args->host->port, sizeof(conn_args->host->port));
840 exim_sha_update_string(h, conn_args->sending_ip_address);
841 exim_sha_update_string(h, openssl_options);
842 exim_sha_update_string(h, ob->tls_require_ciphers);
843 exim_sha_update_string(h, tlsp->sni);
844 # ifdef EXIM_HAVE_ALPN
845 exim_sha_update_string(h, ob->tls_alpn);
847 exim_sha_finish(h, &b);
848 for (g = string_get(b.len*2+1); b.len-- > 0; )
849 g = string_fmt_append(g, "%02x", *b.data++);
850 tlsp->resume_index = string_from_gstring(g);
851 DEBUG(D_tls) debug_printf("TLS: resume session index %s\n", tlsp->resume_index);
855 #endif /*!DISABLE_TLS*/
856 #endif /*!MACRO_PREDEF*/