1 /*************************************************
2 * Exim - an Internet mail transport agent *
3 *************************************************/
5 /* Copyright (c) University of Cambridge 1995 - 2018 */
6 /* Copyright (c) The Exim Maintainers 2020 */
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
28 #if defined(MACRO_PREDEF) && !defined(DISABLE_TLS)
29 # include "macro_predef.h"
33 # include "tls-openssl.c"
39 static void tls_per_lib_daemon_init(void);
40 static void tls_per_lib_daemon_tick(void);
41 static unsigned tls_server_creds_init(void);
42 static void tls_server_creds_invalidate(void);
43 static void tls_client_creds_init(transport_instance *, BOOL);
44 static void tls_client_creds_invalidate(transport_instance *);
45 static void tls_daemon_creds_reload(void);
46 static BOOL opt_set_and_noexpand(const uschar *);
47 static BOOL opt_unset_or_noexpand(const uschar *);
51 /* This module is compiled only when it is specifically requested in the
52 build-time configuration. However, some compilers don't like compiling empty
53 modules, so keep them happy with a dummy when skipping the rest. Make it
54 reference itself to stop picky compilers complaining that it is unused, and put
55 in a dummy argument to stop even pickier compilers complaining about infinite
59 static void dummy(int x) { dummy(x-1); }
60 #else /* most of the rest of the file */
62 const exim_tlslib_state null_tls_preload = {0};
64 /* Static variables that are used for buffering data by both sets of
65 functions and the common functions below.
67 We're moving away from this; GnuTLS is already using a state, which
68 can switch, so we can do TLS callouts during ACLs. */
70 static const int ssl_xfer_buffer_size = 4096;
72 static uschar *ssl_xfer_buffer = NULL;
73 static int ssl_xfer_buffer_lwm = 0;
74 static int ssl_xfer_buffer_hwm = 0;
75 static int ssl_xfer_eof = FALSE;
76 static BOOL ssl_xfer_error = FALSE;
79 #ifdef EXIM_HAVE_KEVENT
80 # define KEV_SIZE 16 /* Eight file,dir pairs */
81 static struct kevent kev[KEV_SIZE];
82 static int kev_used = 0;
85 static unsigned tls_creds_expire = 0;
87 /*************************************************
88 * Expand string; give error on failure *
89 *************************************************/
91 /* If expansion is forced to fail, set the result NULL and return TRUE.
92 Other failures return FALSE. For a server, an SMTP response is given.
95 s the string to expand; if NULL just return TRUE
96 name name of string being expanded (for error)
97 result where to put the result
99 Returns: TRUE if OK; result may still be NULL after forced failure
103 expand_check(const uschar *s, const uschar *name, uschar **result, uschar ** errstr)
107 else if ( !(*result = expand_string(US s)) /* need to clean up const more */
108 && !f.expand_string_forcedfail
111 *errstr = US"Internal error";
112 log_write(0, LOG_MAIN|LOG_PANIC, "expansion of %s failed: %s", name,
113 expand_string_message);
120 #if defined(EXIM_HAVE_INOTIFY) || defined(EXIM_HAVE_KEVENT)
121 /* Add the directory for a filename to the inotify handle, creating that if
122 needed. This is enough to see changes to files in that dir.
123 Return boolean success.
125 The word "system" fails, which is on the safe side as we don't know what
126 directory it implies nor if the TLS library handles a watch for us.
128 The string "system,cache" is recognised and explicitly accepted without
129 setting a watch. This permits the system CA bundle to be cached even though
130 we have no way to tell when it gets modified by an update.
131 The call chain for OpenSSL uses a (undocumented) call into the library
132 to discover the actual file. We don't know what GnuTLS uses.
134 A full set of caching including the CAs takes 35ms output off of the
135 server tls_init() (GnuTLS, Fedora 32, 2018-class x86_64 laptop hardware).
138 tls_set_one_watch(const uschar * filename)
139 # ifdef EXIM_HAVE_INOTIFY
143 if (Ustrcmp(filename, "system,cache") == 0) return TRUE;
145 if (!(s = Ustrrchr(filename, '/'))) return FALSE;
146 s = string_copyn(filename, s - filename); /* mem released by tls_set_watch */
147 DEBUG(D_tls) debug_printf("watch dir '%s'\n", s);
149 /*XXX unclear what effect symlinked files will have for inotify */
151 if (inotify_add_watch(tls_watch_fd, CCS s,
152 IN_ONESHOT | IN_CLOSE_WRITE | IN_DELETE | IN_DELETE_SELF
153 | IN_MOVED_FROM | IN_MOVED_TO | IN_MOVE_SELF) >= 0)
155 DEBUG(D_tls) debug_printf("notify_add_watch: %s\n", strerror(errno));
159 # ifdef EXIM_HAVE_KEVENT
162 int fd1, fd2, i, j, cnt = 0;
165 struct kevent k_dummy;
166 struct timespec ts = {0};
170 if (Ustrcmp(filename, "system,cache") == 0) return TRUE;
174 if (kev_used > KEV_SIZE-2) { s = US"out of kev space"; goto bad; }
175 if (!(s = Ustrrchr(filename, '/'))) return FALSE;
176 s = string_copyn(filename, s - filename); /* mem released by tls_set_watch */
178 /* The dir open will fail if there is a symlink on the path. Fine; it's too
179 much effort to handle all possible cases; just refuse the preload. */
181 if ((fd2 = open(CCS s, O_RDONLY | O_NOFOLLOW)) < 0) { s = US"open dir"; goto bad; }
183 if ((lstat(CCS filename, &sb)) < 0) { s = US"lstat"; goto bad; }
184 if (!S_ISLNK(sb.st_mode))
186 if ((fd1 = open(CCS filename, O_RDONLY | O_NOFOLLOW)) < 0)
187 { s = US"open file"; goto bad; }
188 DEBUG(D_tls) debug_printf("watch file '%s'\n", filename);
189 EV_SET(&kev[++kev_used],
192 EV_ADD | EV_ENABLE | EV_ONESHOT,
193 NOTE_DELETE | NOTE_WRITE | NOTE_EXTEND
194 | NOTE_ATTRIB | NOTE_RENAME | NOTE_REVOKE,
199 DEBUG(D_tls) debug_printf("watch dir '%s'\n", s);
200 EV_SET(&kev[++kev_used],
203 EV_ADD | EV_ENABLE | EV_ONESHOT,
204 NOTE_DELETE | NOTE_WRITE | NOTE_EXTEND
205 | NOTE_ATTRIB | NOTE_RENAME | NOTE_REVOKE,
210 if (!(S_ISLNK(sb.st_mode))) break;
212 t = store_get(1024, FALSE);
213 Ustrncpy(t, s, 1022);
216 if ((i = readlink(CCS filename, (void *)(t+j), 1023-j)) < 0) { s = US"readlink"; goto bad; }
219 store_release_above(t+1);
223 if (kevent(tls_watch_fd, &kev[kev_used-cnt], cnt, &k_dummy, 1, &ts) >= 0)
226 if (kevent(tls_watch_fd, &kev[kev_used-cnt], cnt, NULL, 0, NULL) >= 0)
234 debug_printf("%s: %s: %s\n", __FUNCTION__, s, strerror(errno));
236 debug_printf("%s: %s\n", __FUNCTION__, s);
239 # endif /*EXIM_HAVE_KEVENT*/
242 /* Create an inotify facility if needed.
243 Then set watches on the dir containing the given file or (optionally)
244 list of files. Return boolean success. */
247 tls_set_watch(const uschar * filename, BOOL list)
252 if (!filename || !*filename) return TRUE;
253 if (Ustrncmp(filename, "system", 6) == 0) return TRUE;
255 DEBUG(D_tls) debug_printf("tls_set_watch: '%s'\n", filename);
257 if ( tls_watch_fd < 0
258 # ifdef EXIM_HAVE_INOTIFY
259 && (tls_watch_fd = inotify_init1(O_CLOEXEC)) < 0
261 # ifdef EXIM_HAVE_KEVENT
262 && (tls_watch_fd = kqueue()) < 0
266 DEBUG(D_tls) debug_printf("inotify_init: %s\n", strerror(errno));
275 for (uschar * s; s = string_nextinlist(&filename, &sep, NULL, 0); )
276 if (!(rc = tls_set_one_watch(s))) break;
279 rc = tls_set_one_watch(filename);
282 if (!rc) DEBUG(D_tls) debug_printf("tls_set_watch() fail on '%s': %s\n", filename, strerror(errno));
288 tls_watch_discard_event(int fd)
290 #ifdef EXIM_HAVE_INOTIFY
291 (void) read(fd, big_buffer, big_buffer_size);
293 #ifdef EXIM_HAVE_KEVENT
295 struct timespec t = {0};
296 (void) kevent(fd, NULL, 0, &kev, 1, &t);
299 #endif /*EXIM_HAVE_INOTIFY*/
303 tls_client_creds_reload(BOOL watch)
305 for(transport_instance * t = transports; t; t = t->next)
306 if (Ustrcmp(t->driver_name, "smtp") == 0)
308 tls_client_creds_invalidate(t);
309 tls_client_creds_init(t, watch);
315 tls_watch_invalidate(void)
317 if (tls_watch_fd < 0) return;
319 #ifdef EXIM_HAVE_KEVENT
320 /* Close the files we had open for kevent */
321 for (int i = 0; i < kev_used; i++)
323 (void) close((int) kev[i].ident);
324 kev[i].ident = (uintptr_t)-1;
335 tls_daemon_creds_reload(void)
339 #ifdef EXIM_HAVE_KEVENT
340 tls_watch_invalidate();
343 tls_server_creds_invalidate();
344 tls_creds_expire = (lifetime = tls_server_creds_init())
345 ? time(NULL) + lifetime : 0;
347 tls_client_creds_reload(TRUE);
351 /* Utility predicates for use by the per-library code */
353 opt_set_and_noexpand(const uschar * opt)
354 { return opt && *opt && Ustrchr(opt, '$') == NULL; }
357 opt_unset_or_noexpand(const uschar * opt)
358 { return !opt || Ustrchr(opt, '$') == NULL; }
362 /* Called every time round the daemon loop */
365 tls_daemon_tick(void)
367 tls_per_lib_daemon_tick();
368 #if defined(EXIM_HAVE_INOTIFY) || defined(EXIM_HAVE_KEVENT)
369 if (tls_creds_expire && time(NULL) >= tls_creds_expire)
371 /* The server cert is a selfsign, with limited lifetime. Dump it and
372 generate a new one. Reload the rest of the creds also as the machinery
375 DEBUG(D_tls) debug_printf("selfsign cert rotate\n");
376 tls_creds_expire = 0;
377 tls_daemon_creds_reload();
379 else if (tls_watch_trigger_time && time(NULL) >= tls_watch_trigger_time + 5)
381 /* Called, after a delay for multiple file ops to get done, from
382 the daemon when any of the watches added (above) fire.
383 Dump the set of watches and arrange to reload cached creds (which
384 will set up new watches). */
386 DEBUG(D_tls) debug_printf("watch triggered\n");
387 tls_watch_trigger_time = tls_creds_expire = 0;
388 tls_daemon_creds_reload();
393 /* Called once at daemon startup */
396 tls_daemon_init(void)
398 tls_per_lib_daemon_init();
402 /*************************************************
403 * Timezone environment flipping *
404 *************************************************/
409 uschar * old = US getenv("TZ");
410 (void) setenv("TZ", CCS tz, 1);
416 restore_tz(uschar * tz)
419 (void) setenv("TZ", CCS tz, 1);
421 (void) os_unsetenv(US"TZ");
425 /*************************************************
426 * Many functions are package-specific *
427 *************************************************/
430 # include "tls-gnu.c"
431 # include "tlscert-gnu.c"
432 # define ssl_xfer_buffer (state_server.xfer_buffer)
433 # define ssl_xfer_buffer_lwm (state_server.xfer_buffer_lwm)
434 # define ssl_xfer_buffer_hwm (state_server.xfer_buffer_hwm)
435 # define ssl_xfer_eof (state_server.xfer_eof)
436 # define ssl_xfer_error (state_server.xfer_error)
440 # include "tls-openssl.c"
441 # include "tlscert-openssl.c"
446 /*************************************************
447 * TLS version of ungetc *
448 *************************************************/
450 /* Puts a character back in the input buffer. Only ever
452 Only used by the server-side TLS.
457 Returns: the character
463 if (ssl_xfer_buffer_lwm <= 0)
464 log_write(0, LOG_MAIN|LOG_PANIC_DIE, "buffer underflow in tls_ungetc");
466 ssl_xfer_buffer[--ssl_xfer_buffer_lwm] = ch;
472 /*************************************************
473 * TLS version of feof *
474 *************************************************/
476 /* Tests for a previous EOF
477 Only used by the server-side TLS.
480 Returns: non-zero if the eof flag is set
486 return (int)ssl_xfer_eof;
491 /*************************************************
492 * TLS version of ferror *
493 *************************************************/
495 /* Tests for a previous read error, and returns with errno
496 restored to what it was when the error was detected.
497 Only used by the server-side TLS.
499 >>>>> Hmm. Errno not handled yet. Where do we get it from? >>>>>
502 Returns: non-zero if the error flag is set
508 return (int)ssl_xfer_error;
512 /*************************************************
513 * TLS version of smtp_buffered *
514 *************************************************/
516 /* Tests for unused chars in the TLS input buffer.
517 Only used by the server-side TLS.
524 tls_smtp_buffered(void)
526 return ssl_xfer_buffer_lwm < ssl_xfer_buffer_hwm;
530 #endif /*DISABLE_TLS*/
533 tls_modify_variables(tls_support * dest_tsp)
535 modify_variable(US"tls_bits", &dest_tsp->bits);
536 modify_variable(US"tls_certificate_verified", &dest_tsp->certificate_verified);
537 modify_variable(US"tls_cipher", &dest_tsp->cipher);
538 modify_variable(US"tls_peerdn", &dest_tsp->peerdn);
540 modify_variable(US"tls_sni", &dest_tsp->sni);
546 /************************************************
547 * TLS certificate name operations *
548 ************************************************/
550 /* Convert an rfc4514 DN to an exim comma-sep list.
551 Backslashed commas need to be replaced by doublecomma
552 for Exim's list quoting. We modify the given string
557 dn_to_list(uschar * dn)
559 for (uschar * cp = dn; *cp; cp++)
560 if (cp[0] == '\\' && cp[1] == ',')
565 /* Extract fields of a given type from an RFC4514-
566 format Distinguished Name. Return an Exim list.
567 NOTE: We modify the supplied dn string during operation.
570 dn Distinguished Name string
571 mod list containing optional output list-sep and
572 field selector match, comma-separated
574 allocated string with list of matching fields,
579 tls_field_from_dn(uschar * dn, const uschar * mod)
582 uschar outsep = '\n';
584 uschar * match = NULL;
586 gstring * list = NULL;
588 while ((ele = string_nextinlist(&mod, &insep, NULL, 0)))
590 match = ele; /* field tag to match */
592 outsep = ele[1]; /* nondefault output separator */
596 len = match ? Ustrlen(match) : -1;
597 while ((ele = string_nextinlist(CUSS &dn, &insep, NULL, 0)))
599 || Ustrncmp(ele, match, len) == 0 && ele[len] == '='
601 list = string_append_listele(list, outsep, ele+len+1);
602 return string_from_gstring(list);
606 /* Compare a domain name with a possibly-wildcarded name. Wildcards
607 are restricted to a single one, as the first element of patterns
608 having at least three dot-separated elements. Case-independent.
609 Return TRUE for a match
612 is_name_match(const uschar * name, const uschar * pat)
615 return *pat == '*' /* possible wildcard match */
616 ? *++pat == '.' /* starts star, dot */
617 && !Ustrchr(++pat, '*') /* has no more stars */
618 && Ustrchr(pat, '.') /* and has another dot. */
619 && (cp = Ustrchr(name, '.'))/* The name has at least one dot */
620 && strcmpic(++cp, pat) == 0 /* and we only compare after it. */
621 : !Ustrchr(pat+1, '*')
622 && strcmpic(name, pat) == 0;
625 /* Compare a list of names with the dnsname elements
626 of the Subject Alternate Name, if any, and the
630 namelist names to compare
638 tls_is_name_for_cert(const uschar * namelist, void * cert)
640 uschar * altnames = tls_cert_subject_altname(cert, US"dns");
646 if ((altnames = tls_cert_subject_altname(cert, US"dns")))
649 while ((cmpname = string_nextinlist(&namelist, &cmp_sep, NULL, 0)))
651 const uschar * an = altnames;
652 while ((certname = string_nextinlist(&an, &alt_sep, NULL, 0)))
653 if (is_name_match(cmpname, certname))
658 else if ((subjdn = tls_cert_subject(cert, NULL)))
663 while ((cmpname = string_nextinlist(&namelist, &cmp_sep, NULL, 0)))
665 const uschar * sn = subjdn;
666 while ((certname = string_nextinlist(&sn, &sn_sep, NULL, 0)))
667 if ( *certname++ == 'C'
668 && *certname++ == 'N'
669 && *certname++ == '='
670 && is_name_match(cmpname, certname)
679 /* Environment cleanup: The GnuTLS library uses SSLKEYLOGFILE in the environment
680 and writes a file by that name. Our OpenSSL code does the same, using keying
681 info from the library API.
682 The GnuTLS support only works if exim is run by root, not taking advantage of
684 You can use either the external environment (modulo the keep_environment config)
685 or the add_environment config option for SSLKEYLOGFILE; the latter takes
688 If the path is absolute, require it starts with the spooldir; otherwise delete
689 the env variable. If relative, prefix the spooldir.
694 uschar * path = US getenv("SSLKEYLOGFILE");
697 unsetenv("SSLKEYLOGFILE");
698 else if (*path != '/')
701 debug_printf("prepending spooldir to env SSLKEYLOGFILE\n");
702 setenv("SSLKEYLOGFILE", CCS string_sprintf("%s/%s", spool_directory, path), 1);
704 else if (Ustrncmp(path, spool_directory, Ustrlen(spool_directory)) != 0)
707 debug_printf("removing env SSLKEYLOGFILE=%s: not under spooldir\n", path);
708 unsetenv("SSLKEYLOGFILE");
712 /*************************************************
713 * Drop privs for checking TLS config *
714 *************************************************/
716 /* We want to validate TLS options during readconf, but do not want to be
717 root when we call into the TLS library, in case of library linkage errors
718 which cause segfaults; before this check, those were always done as the Exim
719 runtime user and it makes sense to continue with that.
721 Assumes: tls_require_ciphers has been set, if it will be
722 exim_user has been set, if it will be
723 exim_group has been set, if it will be
725 Returns: bool for "okay"; false will cause caller to immediately exit.
729 tls_dropprivs_validate_require_cipher(BOOL nowarn)
731 const uschar *errmsg;
734 void (*oldsignal)(int);
736 /* If TLS will never be used, no point checking ciphers */
738 if ( !tls_advertise_hosts
739 || !*tls_advertise_hosts
740 || Ustrcmp(tls_advertise_hosts, ":") == 0
743 else if (!nowarn && !tls_certificate)
744 log_write(0, LOG_MAIN,
745 "Warning: No server certificate defined; will use a selfsigned one.\n"
746 " Suggested action: either install a certificate or change tls_advertise_hosts option");
748 oldsignal = signal(SIGCHLD, SIG_DFL);
751 if ((pid = exim_fork(US"cipher-validate")) < 0)
752 log_write(0, LOG_MAIN|LOG_PANIC_DIE, "fork failed for TLS check");
756 /* in some modes, will have dropped privilege already */
758 exim_setugid(exim_uid, exim_gid, FALSE,
759 US"calling tls_validate_require_cipher");
761 if ((errmsg = tls_validate_require_cipher()))
762 log_write(0, LOG_PANIC_DIE|LOG_CONFIG,
763 "tls_require_ciphers invalid: %s", errmsg);
765 exim_underbar_exit(EXIT_SUCCESS);
769 rc = waitpid(pid, &status, 0);
770 } while (rc < 0 && errno == EINTR);
773 debug_printf("tls_validate_require_cipher child %d ended: status=0x%x\n",
776 signal(SIGCHLD, oldsignal);
784 #endif /*!DISABLE_TLS*/
785 #endif /*!MACRO_PREDEF*/