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 void 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 /*************************************************
86 * Expand string; give error on failure *
87 *************************************************/
89 /* If expansion is forced to fail, set the result NULL and return TRUE.
90 Other failures return FALSE. For a server, an SMTP response is given.
93 s the string to expand; if NULL just return TRUE
94 name name of string being expanded (for error)
95 result where to put the result
97 Returns: TRUE if OK; result may still be NULL after forced failure
101 expand_check(const uschar *s, const uschar *name, uschar **result, uschar ** errstr)
105 else if ( !(*result = expand_string(US s)) /* need to clean up const more */
106 && !f.expand_string_forcedfail
109 *errstr = US"Internal error";
110 log_write(0, LOG_MAIN|LOG_PANIC, "expansion of %s failed: %s", name,
111 expand_string_message);
118 #if defined(EXIM_HAVE_INOTIFY) || defined(EXIM_HAVE_KEVENT)
119 /* Add the directory for a filename to the inotify handle, creating that if
120 needed. This is enough to see changes to files in that dir.
121 Return boolean success.
123 The word "system" fails, which is on the safe side as we don't know what
124 directory it implies nor if the TLS library handles a watch for us.
126 The string "system,cache" is recognised and explicitly accepted without
127 setting a watch. This permits the system CA bundle to be cached even though
128 we have no way to tell when it gets modified by an update.
129 The call chain for OpenSSL uses a (undocumented) call into the library
130 to discover the actual file. We don't know what GnuTLS uses.
132 A full set of caching including the CAs takes 35ms output off of the
133 server tls_init() (GnuTLS, Fedora 32, 2018-class x86_64 laptop hardware).
136 tls_set_one_watch(const uschar * filename)
137 # ifdef EXIM_HAVE_INOTIFY
141 if (Ustrcmp(filename, "system,cache") == 0) return TRUE;
143 if (!(s = Ustrrchr(filename, '/'))) return FALSE;
144 s = string_copyn(filename, s - filename); /* mem released by tls_set_watch */
145 DEBUG(D_tls) debug_printf("watch dir '%s'\n", s);
147 /*XXX unclear what effect symlinked files will have for inotify */
149 if (inotify_add_watch(tls_watch_fd, CCS s,
150 IN_ONESHOT | IN_CLOSE_WRITE | IN_DELETE | IN_DELETE_SELF
151 | IN_MOVED_FROM | IN_MOVED_TO | IN_MOVE_SELF) >= 0)
153 DEBUG(D_tls) debug_printf("notify_add_watch: %s\n", strerror(errno));
157 # ifdef EXIM_HAVE_KEVENT
160 int fd1, fd2, i, cnt = 0;
164 if (Ustrcmp(filename, "system,cache") == 0) return TRUE;
168 if (!(s = Ustrrchr(filename, '/'))) return FALSE;
169 if ((lstat(CCS filename, &sb)) < 0) { s = US"lstat"; goto bad; }
170 if (kev_used > KEV_SIZE-2) { s = US"out of kev space"; goto bad; }
172 /* The dir open will fail if there is a symlink on the path. Fine; it's too
173 much effort to handle all possible cases; just refuse the preload. */
175 if ((fd2 = open(CCS s, O_RDONLY | O_NOFOLLOW)) < 0) { s = US"open dir"; goto bad; }
177 if (!S_ISLNK(sb.st_mode))
179 if ((fd1 = open(CCS filename, O_RDONLY | O_NOFOLLOW)) < 0)
180 { s = US"open file"; goto bad; }
181 DEBUG(D_tls) debug_printf("watch file '%s'\n", filename);
182 EV_SET(&kev[++kev_used],
185 EV_ADD | EV_ENABLE | EV_ONESHOT,
186 NOTE_DELETE | NOTE_WRITE | NOTE_EXTEND
187 | NOTE_ATTRIB | NOTE_RENAME | NOTE_REVOKE,
192 DEBUG(D_tls) debug_printf("watch dir '%s'\n", s);
193 EV_SET(&kev[++kev_used],
196 EV_ADD | EV_ENABLE | EV_ONESHOT,
197 NOTE_DELETE | NOTE_WRITE | NOTE_EXTEND
198 | NOTE_ATTRIB | NOTE_RENAME | NOTE_REVOKE,
203 if (!(S_ISLNK(sb.st_mode))) break;
205 s = store_get(1024, FALSE);
206 if ((i = readlink(CCS filename, s, 1024)) < 0) { s = US"readlink"; goto bad; }
209 store_release_above(s+1);
212 if (kevent(tls_watch_fd, &kev[kev_used-cnt], cnt, NULL, 0, NULL) >= 0)
219 debug_printf("%s: %s: %s\n", __FUNCTION__, s, strerror(errno));
221 debug_printf("%s: %s\n", __FUNCTION__, s);
224 # endif /*EXIM_HAVE_KEVENT*/
227 /* Create an inotify facility if needed.
228 Then set watches on the dir containing the given file or (optionally)
229 list of files. Return boolean success. */
232 tls_set_watch(const uschar * filename, BOOL list)
237 if (!filename || !*filename) return TRUE;
238 if (Ustrncmp(filename, "system", 6) == 0) return TRUE;
240 DEBUG(D_tls) debug_printf("tls_set_watch: '%s'\n", filename);
242 if ( tls_watch_fd < 0
243 # ifdef EXIM_HAVE_INOTIFY
244 && (tls_watch_fd = inotify_init1(O_CLOEXEC)) < 0
246 # ifdef EXIM_HAVE_KEVENT
247 && (tls_watch_fd = kqueue()) < 0
251 DEBUG(D_tls) debug_printf("inotify_init: %s\n", strerror(errno));
260 for (uschar * s; s = string_nextinlist(&filename, &sep, NULL, 0); )
261 if (!(rc = tls_set_one_watch(s))) break;
264 rc = tls_set_one_watch(filename);
267 if (!rc) DEBUG(D_tls) debug_printf("tls_set_watch() fail on '%s': %s\n", filename, strerror(errno));
273 tls_watch_discard_event(int fd)
275 #ifdef EXIM_HAVE_INOTIFY
276 (void) read(fd, big_buffer, big_buffer_size);
278 #ifdef EXIM_HAVE_KEVENT
280 struct timespec t = {0};
281 (void) kevent(fd, NULL, 0, &kev, 1, &t);
285 /* Called, after a delay for multiple file ops to get done, from
286 the daemon when any of the watches added (above) fire.
288 Dump the set of watches and arrange to reload cached creds (which
289 will set up new watches). */
292 tls_watch_triggered(void)
294 DEBUG(D_tls) debug_printf("watch triggered\n");
296 tls_daemon_creds_reload();
298 #endif /*EXIM_HAVE_INOTIFY*/
302 tls_client_creds_reload(BOOL watch)
304 for(transport_instance * t = transports; t; t = t->next)
305 if (Ustrcmp(t->driver_name, "smtp") == 0)
307 tls_client_creds_invalidate(t);
308 tls_client_creds_init(t, watch);
314 tls_watch_invalidate(void)
316 if (tls_watch_fd < 0) return;
318 #ifdef EXIM_HAVE_KEVENT
319 /* Close the files we had open for kevent */
320 for (int fd, i = 0; i < kev_used; i++)
322 (void) close((int) kev[i].ident);
323 kev[i].ident = (uintptr_t)-1;
334 tls_daemon_creds_reload(void)
336 #ifdef EXIM_HAVE_KEVENT
337 tls_watch_invalidate();
340 tls_server_creds_invalidate();
341 tls_server_creds_init();
343 tls_client_creds_reload(TRUE);
347 /* Utility predicates for use by the per-library code */
349 opt_set_and_noexpand(const uschar * opt)
350 { return opt && *opt && Ustrchr(opt, '$') == NULL; }
353 opt_unset_or_noexpand(const uschar * opt)
354 { return !opt || Ustrchr(opt, '$') == NULL; }
358 /* Called every time round the daemon loop */
361 tls_daemon_tick(void)
363 tls_per_lib_daemon_tick();
364 #if defined(EXIM_HAVE_INOTIFY) || defined(EXIM_HAVE_KEVENT)
365 if (tls_watch_trigger_time && time(NULL) >= tls_watch_trigger_time + 5)
367 tls_watch_trigger_time = 0;
368 tls_watch_triggered();
373 /* Called once at daemon startup */
376 tls_daemon_init(void)
378 tls_per_lib_daemon_init();
382 /*************************************************
383 * Timezone environment flipping *
384 *************************************************/
389 uschar * old = US getenv("TZ");
390 (void) setenv("TZ", CCS tz, 1);
396 restore_tz(uschar * tz)
399 (void) setenv("TZ", CCS tz, 1);
401 (void) os_unsetenv(US"TZ");
405 /*************************************************
406 * Many functions are package-specific *
407 *************************************************/
410 # include "tls-gnu.c"
411 # include "tlscert-gnu.c"
412 # define ssl_xfer_buffer (state_server.xfer_buffer)
413 # define ssl_xfer_buffer_lwm (state_server.xfer_buffer_lwm)
414 # define ssl_xfer_buffer_hwm (state_server.xfer_buffer_hwm)
415 # define ssl_xfer_eof (state_server.xfer_eof)
416 # define ssl_xfer_error (state_server.xfer_error)
420 # include "tls-openssl.c"
421 # include "tlscert-openssl.c"
426 /*************************************************
427 * TLS version of ungetc *
428 *************************************************/
430 /* Puts a character back in the input buffer. Only ever
432 Only used by the server-side TLS.
437 Returns: the character
443 ssl_xfer_buffer[--ssl_xfer_buffer_lwm] = ch;
449 /*************************************************
450 * TLS version of feof *
451 *************************************************/
453 /* Tests for a previous EOF
454 Only used by the server-side TLS.
457 Returns: non-zero if the eof flag is set
463 return (int)ssl_xfer_eof;
468 /*************************************************
469 * TLS version of ferror *
470 *************************************************/
472 /* Tests for a previous read error, and returns with errno
473 restored to what it was when the error was detected.
474 Only used by the server-side TLS.
476 >>>>> Hmm. Errno not handled yet. Where do we get it from? >>>>>
479 Returns: non-zero if the error flag is set
485 return (int)ssl_xfer_error;
489 /*************************************************
490 * TLS version of smtp_buffered *
491 *************************************************/
493 /* Tests for unused chars in the TLS input buffer.
494 Only used by the server-side TLS.
501 tls_smtp_buffered(void)
503 return ssl_xfer_buffer_lwm < ssl_xfer_buffer_hwm;
507 #endif /*DISABLE_TLS*/
510 tls_modify_variables(tls_support * dest_tsp)
512 modify_variable(US"tls_bits", &dest_tsp->bits);
513 modify_variable(US"tls_certificate_verified", &dest_tsp->certificate_verified);
514 modify_variable(US"tls_cipher", &dest_tsp->cipher);
515 modify_variable(US"tls_peerdn", &dest_tsp->peerdn);
517 modify_variable(US"tls_sni", &dest_tsp->sni);
523 /************************************************
524 * TLS certificate name operations *
525 ************************************************/
527 /* Convert an rfc4514 DN to an exim comma-sep list.
528 Backslashed commas need to be replaced by doublecomma
529 for Exim's list quoting. We modify the given string
534 dn_to_list(uschar * dn)
536 for (uschar * cp = dn; *cp; cp++)
537 if (cp[0] == '\\' && cp[1] == ',')
542 /* Extract fields of a given type from an RFC4514-
543 format Distinguished Name. Return an Exim list.
544 NOTE: We modify the supplied dn string during operation.
547 dn Distinguished Name string
548 mod list containing optional output list-sep and
549 field selector match, comma-separated
551 allocated string with list of matching fields,
556 tls_field_from_dn(uschar * dn, const uschar * mod)
559 uschar outsep = '\n';
561 uschar * match = NULL;
563 gstring * list = NULL;
565 while ((ele = string_nextinlist(&mod, &insep, NULL, 0)))
567 match = ele; /* field tag to match */
569 outsep = ele[1]; /* nondefault output separator */
573 len = match ? Ustrlen(match) : -1;
574 while ((ele = string_nextinlist(CUSS &dn, &insep, NULL, 0)))
576 || Ustrncmp(ele, match, len) == 0 && ele[len] == '='
578 list = string_append_listele(list, outsep, ele+len+1);
579 return string_from_gstring(list);
583 /* Compare a domain name with a possibly-wildcarded name. Wildcards
584 are restricted to a single one, as the first element of patterns
585 having at least three dot-separated elements. Case-independent.
586 Return TRUE for a match
589 is_name_match(const uschar * name, const uschar * pat)
592 return *pat == '*' /* possible wildcard match */
593 ? *++pat == '.' /* starts star, dot */
594 && !Ustrchr(++pat, '*') /* has no more stars */
595 && Ustrchr(pat, '.') /* and has another dot. */
596 && (cp = Ustrchr(name, '.'))/* The name has at least one dot */
597 && strcmpic(++cp, pat) == 0 /* and we only compare after it. */
598 : !Ustrchr(pat+1, '*')
599 && strcmpic(name, pat) == 0;
602 /* Compare a list of names with the dnsname elements
603 of the Subject Alternate Name, if any, and the
607 namelist names to compare
615 tls_is_name_for_cert(const uschar * namelist, void * cert)
617 uschar * altnames = tls_cert_subject_altname(cert, US"dns");
623 if ((altnames = tls_cert_subject_altname(cert, US"dns")))
626 while ((cmpname = string_nextinlist(&namelist, &cmp_sep, NULL, 0)))
628 const uschar * an = altnames;
629 while ((certname = string_nextinlist(&an, &alt_sep, NULL, 0)))
630 if (is_name_match(cmpname, certname))
635 else if ((subjdn = tls_cert_subject(cert, NULL)))
640 while ((cmpname = string_nextinlist(&namelist, &cmp_sep, NULL, 0)))
642 const uschar * sn = subjdn;
643 while ((certname = string_nextinlist(&sn, &sn_sep, NULL, 0)))
644 if ( *certname++ == 'C'
645 && *certname++ == 'N'
646 && *certname++ == '='
647 && is_name_match(cmpname, certname)
656 /* Environment cleanup: The GnuTLS library uses SSLKEYLOGFILE in the environment
657 and writes a file by that name. Our OpenSSL code does the same, using keying
658 info from the library API.
659 The GnuTLS support only works if exim is run by root, not taking advantage of
661 You can use either the external environment (modulo the keep_environment config)
662 or the add_environment config option for SSLKEYLOGFILE; the latter takes
665 If the path is absolute, require it starts with the spooldir; otherwise delete
666 the env variable. If relative, prefix the spooldir.
671 uschar * path = US getenv("SSLKEYLOGFILE");
674 unsetenv("SSLKEYLOGFILE");
675 else if (*path != '/')
678 debug_printf("prepending spooldir to env SSLKEYLOGFILE\n");
679 setenv("SSLKEYLOGFILE", CCS string_sprintf("%s/%s", spool_directory, path), 1);
681 else if (Ustrncmp(path, spool_directory, Ustrlen(spool_directory)) != 0)
684 debug_printf("removing env SSLKEYLOGFILE=%s: not under spooldir\n", path);
685 unsetenv("SSLKEYLOGFILE");
689 /*************************************************
690 * Drop privs for checking TLS config *
691 *************************************************/
693 /* We want to validate TLS options during readconf, but do not want to be
694 root when we call into the TLS library, in case of library linkage errors
695 which cause segfaults; before this check, those were always done as the Exim
696 runtime user and it makes sense to continue with that.
698 Assumes: tls_require_ciphers has been set, if it will be
699 exim_user has been set, if it will be
700 exim_group has been set, if it will be
702 Returns: bool for "okay"; false will cause caller to immediately exit.
706 tls_dropprivs_validate_require_cipher(BOOL nowarn)
708 const uschar *errmsg;
711 void (*oldsignal)(int);
713 /* If TLS will never be used, no point checking ciphers */
715 if ( !tls_advertise_hosts
716 || !*tls_advertise_hosts
717 || Ustrcmp(tls_advertise_hosts, ":") == 0
720 else if (!nowarn && !tls_certificate)
721 log_write(0, LOG_MAIN,
722 "Warning: No server certificate defined; will use a selfsigned one.\n"
723 " Suggested action: either install a certificate or change tls_advertise_hosts option");
725 oldsignal = signal(SIGCHLD, SIG_DFL);
728 if ((pid = exim_fork(US"cipher-validate")) < 0)
729 log_write(0, LOG_MAIN|LOG_PANIC_DIE, "fork failed for TLS check");
733 /* in some modes, will have dropped privilege already */
735 exim_setugid(exim_uid, exim_gid, FALSE,
736 US"calling tls_validate_require_cipher");
738 if ((errmsg = tls_validate_require_cipher()))
739 log_write(0, LOG_PANIC_DIE|LOG_CONFIG,
740 "tls_require_ciphers invalid: %s", errmsg);
742 exim_underbar_exit(EXIT_SUCCESS);
746 rc = waitpid(pid, &status, 0);
747 } while (rc < 0 && errno == EINTR);
750 debug_printf("tls_validate_require_cipher child %d ended: status=0x%x\n",
753 signal(SIGCHLD, oldsignal);
761 #endif /*!DISABLE_TLS*/
762 #endif /*!MACRO_PREDEF*/