1 /*************************************************
2 * Exim - an Internet mail transport agent *
3 *************************************************/
5 /* Copyright (c) University of Cambridge 1995 - 2018 */
6 /* Copyright (c) The Exim Maintainers 2020 - 2021 */
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':\t%d\n", filename, fd1);
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':\t%d\n", s, fd2);
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 DEBUG(D_tls) debug_printf("closing watch fd: %d\n", (int) kev[i].ident);
324 (void) close((int) kev[i].ident);
325 kev[i].ident = (uintptr_t)-1;
336 tls_daemon_creds_reload(void)
340 #ifdef EXIM_HAVE_KEVENT
341 tls_watch_invalidate();
344 tls_server_creds_invalidate();
345 tls_creds_expire = (lifetime = tls_server_creds_init())
346 ? time(NULL) + lifetime : 0;
348 tls_client_creds_reload(TRUE);
352 /* Utility predicates for use by the per-library code */
354 opt_set_and_noexpand(const uschar * opt)
355 { return opt && *opt && Ustrchr(opt, '$') == NULL; }
358 opt_unset_or_noexpand(const uschar * opt)
359 { return !opt || Ustrchr(opt, '$') == NULL; }
363 /* Called every time round the daemon loop.
365 If we reloaded fd-watcher, return the old watch fd
366 having modified the global for the new one. Otherwise
371 tls_daemon_tick(void)
373 int old_watch_fd = tls_watch_fd;
375 tls_per_lib_daemon_tick();
376 #if defined(EXIM_HAVE_INOTIFY) || defined(EXIM_HAVE_KEVENT)
377 if (tls_creds_expire && time(NULL) >= tls_creds_expire)
379 /* The server cert is a selfsign, with limited lifetime. Dump it and
380 generate a new one. Reload the rest of the creds also as the machinery
383 DEBUG(D_tls) debug_printf("selfsign cert rotate\n");
384 tls_creds_expire = 0;
385 tls_daemon_creds_reload();
388 else if (tls_watch_trigger_time && time(NULL) >= tls_watch_trigger_time + 5)
390 /* Called, after a delay for multiple file ops to get done, from
391 the daemon when any of the watches added (above) fire.
392 Dump the set of watches and arrange to reload cached creds (which
393 will set up new watches). */
395 DEBUG(D_tls) debug_printf("watch triggered\n");
396 tls_watch_trigger_time = tls_creds_expire = 0;
397 tls_daemon_creds_reload();
404 /* Called once at daemon startup */
407 tls_daemon_init(void)
409 tls_per_lib_daemon_init();
413 /*************************************************
414 * Timezone environment flipping *
415 *************************************************/
420 uschar * old = US getenv("TZ");
421 (void) setenv("TZ", CCS tz, 1);
427 restore_tz(uschar * tz)
430 (void) setenv("TZ", CCS tz, 1);
432 (void) os_unsetenv(US"TZ");
436 /*************************************************
437 * Many functions are package-specific *
438 *************************************************/
441 # include "tls-gnu.c"
442 # include "tlscert-gnu.c"
443 # define ssl_xfer_buffer (state_server.xfer_buffer)
444 # define ssl_xfer_buffer_lwm (state_server.xfer_buffer_lwm)
445 # define ssl_xfer_buffer_hwm (state_server.xfer_buffer_hwm)
446 # define ssl_xfer_eof (state_server.xfer_eof)
447 # define ssl_xfer_error (state_server.xfer_error)
451 # include "tls-openssl.c"
452 # include "tlscert-openssl.c"
457 /*************************************************
458 * TLS version of ungetc *
459 *************************************************/
461 /* Puts a character back in the input buffer. Only ever
463 Only used by the server-side TLS.
468 Returns: the character
474 if (ssl_xfer_buffer_lwm <= 0)
475 log_write(0, LOG_MAIN|LOG_PANIC_DIE, "buffer underflow in tls_ungetc");
477 ssl_xfer_buffer[--ssl_xfer_buffer_lwm] = ch;
483 /*************************************************
484 * TLS version of feof *
485 *************************************************/
487 /* Tests for a previous EOF
488 Only used by the server-side TLS.
491 Returns: non-zero if the eof flag is set
497 return (int)ssl_xfer_eof;
502 /*************************************************
503 * TLS version of ferror *
504 *************************************************/
506 /* Tests for a previous read error, and returns with errno
507 restored to what it was when the error was detected.
508 Only used by the server-side TLS.
510 >>>>> Hmm. Errno not handled yet. Where do we get it from? >>>>>
513 Returns: non-zero if the error flag is set
519 return (int)ssl_xfer_error;
523 /*************************************************
524 * TLS version of smtp_buffered *
525 *************************************************/
527 /* Tests for unused chars in the TLS input buffer.
528 Only used by the server-side TLS.
535 tls_smtp_buffered(void)
537 return ssl_xfer_buffer_lwm < ssl_xfer_buffer_hwm;
541 #endif /*DISABLE_TLS*/
544 tls_modify_variables(tls_support * dest_tsp)
546 modify_variable(US"tls_bits", &dest_tsp->bits);
547 modify_variable(US"tls_certificate_verified", &dest_tsp->certificate_verified);
548 modify_variable(US"tls_cipher", &dest_tsp->cipher);
549 modify_variable(US"tls_peerdn", &dest_tsp->peerdn);
551 modify_variable(US"tls_sni", &dest_tsp->sni);
557 /************************************************
558 * TLS certificate name operations *
559 ************************************************/
561 /* Convert an rfc4514 DN to an exim comma-sep list.
562 Backslashed commas need to be replaced by doublecomma
563 for Exim's list quoting. We modify the given string
568 dn_to_list(uschar * dn)
570 for (uschar * cp = dn; *cp; cp++)
571 if (cp[0] == '\\' && cp[1] == ',')
576 /* Extract fields of a given type from an RFC4514-
577 format Distinguished Name. Return an Exim list.
578 NOTE: We modify the supplied dn string during operation.
581 dn Distinguished Name string
582 mod list containing optional output list-sep and
583 field selector match, comma-separated
585 allocated string with list of matching fields,
590 tls_field_from_dn(uschar * dn, const uschar * mod)
593 uschar outsep = '\n';
595 uschar * match = NULL;
597 gstring * list = NULL;
599 while ((ele = string_nextinlist(&mod, &insep, NULL, 0)))
601 match = ele; /* field tag to match */
603 outsep = ele[1]; /* nondefault output separator */
607 len = match ? Ustrlen(match) : -1;
608 while ((ele = string_nextinlist(CUSS &dn, &insep, NULL, 0)))
610 || Ustrncmp(ele, match, len) == 0 && ele[len] == '='
612 list = string_append_listele(list, outsep, ele+len+1);
613 return string_from_gstring(list);
617 /* Compare a domain name with a possibly-wildcarded name. Wildcards
618 are restricted to a single one, as the first element of patterns
619 having at least three dot-separated elements. Case-independent.
620 Return TRUE for a match
623 is_name_match(const uschar * name, const uschar * pat)
626 return *pat == '*' /* possible wildcard match */
627 ? *++pat == '.' /* starts star, dot */
628 && !Ustrchr(++pat, '*') /* has no more stars */
629 && Ustrchr(pat, '.') /* and has another dot. */
630 && (cp = Ustrchr(name, '.'))/* The name has at least one dot */
631 && strcmpic(++cp, pat) == 0 /* and we only compare after it. */
632 : !Ustrchr(pat+1, '*')
633 && strcmpic(name, pat) == 0;
636 /* Compare a list of names with the dnsname elements
637 of the Subject Alternate Name, if any, and the
641 namelist names to compare
649 tls_is_name_for_cert(const uschar * namelist, void * cert)
651 uschar * altnames = tls_cert_subject_altname(cert, US"dns");
657 if ((altnames = tls_cert_subject_altname(cert, US"dns")))
660 while ((cmpname = string_nextinlist(&namelist, &cmp_sep, NULL, 0)))
662 const uschar * an = altnames;
663 while ((certname = string_nextinlist(&an, &alt_sep, NULL, 0)))
664 if (is_name_match(cmpname, certname))
669 else if ((subjdn = tls_cert_subject(cert, NULL)))
674 while ((cmpname = string_nextinlist(&namelist, &cmp_sep, NULL, 0)))
676 const uschar * sn = subjdn;
677 while ((certname = string_nextinlist(&sn, &sn_sep, NULL, 0)))
678 if ( *certname++ == 'C'
679 && *certname++ == 'N'
680 && *certname++ == '='
681 && is_name_match(cmpname, certname)
689 /* Environment cleanup: The GnuTLS library uses SSLKEYLOGFILE in the environment
690 and writes a file by that name. Our OpenSSL code does the same, using keying
691 info from the library API.
692 The GnuTLS support only works if exim is run by root, not taking advantage of
694 You can use either the external environment (modulo the keep_environment config)
695 or the add_environment config option for SSLKEYLOGFILE; the latter takes
698 If the path is absolute, require it starts with the spooldir; otherwise delete
699 the env variable. If relative, prefix the spooldir.
704 uschar * path = US getenv("SSLKEYLOGFILE");
707 unsetenv("SSLKEYLOGFILE");
708 else if (*path != '/')
711 debug_printf("prepending spooldir to env SSLKEYLOGFILE\n");
712 setenv("SSLKEYLOGFILE", CCS string_sprintf("%s/%s", spool_directory, path), 1);
714 else if (Ustrncmp(path, spool_directory, Ustrlen(spool_directory)) != 0)
717 debug_printf("removing env SSLKEYLOGFILE=%s: not under spooldir\n", path);
718 unsetenv("SSLKEYLOGFILE");
722 /*************************************************
723 * Drop privs for checking TLS config *
724 *************************************************/
726 /* We want to validate TLS options during readconf, but do not want to be
727 root when we call into the TLS library, in case of library linkage errors
728 which cause segfaults; before this check, those were always done as the Exim
729 runtime user and it makes sense to continue with that.
731 Assumes: tls_require_ciphers has been set, if it will be
732 exim_user has been set, if it will be
733 exim_group has been set, if it will be
735 Returns: bool for "okay"; false will cause caller to immediately exit.
739 tls_dropprivs_validate_require_cipher(BOOL nowarn)
741 const uschar *errmsg;
744 void (*oldsignal)(int);
746 /* If TLS will never be used, no point checking ciphers */
748 if ( !tls_advertise_hosts
749 || !*tls_advertise_hosts
750 || Ustrcmp(tls_advertise_hosts, ":") == 0
753 else if (!nowarn && !tls_certificate)
754 log_write(0, LOG_MAIN,
755 "Warning: No server certificate defined; will use a selfsigned one.\n"
756 " Suggested action: either install a certificate or change tls_advertise_hosts option");
758 oldsignal = signal(SIGCHLD, SIG_DFL);
761 if ((pid = exim_fork(US"cipher-validate")) < 0)
762 log_write(0, LOG_MAIN|LOG_PANIC_DIE, "fork failed for TLS check");
766 /* in some modes, will have dropped privilege already */
768 exim_setugid(exim_uid, exim_gid, FALSE,
769 US"calling tls_validate_require_cipher");
771 if ((errmsg = tls_validate_require_cipher()))
772 log_write(0, LOG_PANIC_DIE|LOG_CONFIG,
773 "tls_require_ciphers invalid: %s", errmsg);
775 exim_underbar_exit(EXIT_SUCCESS);
779 rc = waitpid(pid, &status, 0);
780 } while (rc < 0 && errno == EINTR);
783 debug_printf("tls_validate_require_cipher child %d ended: status=0x%x\n",
786 signal(SIGCHLD, oldsignal);
794 #endif /*!DISABLE_TLS*/
795 #endif /*!MACRO_PREDEF*/