Adding upstream version 4.94.2.upstream/4.94.2upstream

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 486 insertions, 0 deletions

diff --git a/src/tls.c b/src/tls.c
new file mode 100644
index 0000000..d37a8f9
--- /dev/null
+++ b/src/tls.c
@@ -0,0 +1,486 @@
+/*************************************************
+*     Exim - an Internet mail transport agent    *
+*************************************************/
+
+/* Copyright (c) University of Cambridge 1995 - 2018 */
+/* Copyright (c) The Exim Maintainers 2020 */
+/* See the file NOTICE for conditions of use and distribution. */
+
+/* This module provides TLS (aka SSL) support for Exim. The code for OpenSSL is
+based on a patch that was originally contributed by Steve Haslam. It was
+adapted from stunnel, a GPL program by Michal Trojnara. The code for GNU TLS is
+based on a patch contributed by Nikos Mavrogiannopoulos. Because these packages
+are so very different, the functions for each are kept in separate files. The
+relevant file is #included as required, after any any common functions.
+
+No cryptographic code is included in Exim. All this module does is to call
+functions from the OpenSSL or GNU TLS libraries. */
+
+
+#include "exim.h"
+#include "transports/smtp.h"
+
+#if !defined(DISABLE_TLS) && !defined(USE_OPENSSL) && !defined(USE_GNUTLS)
+# error One of USE_OPENSSL or USE_GNUTLS must be defined for a TLS build
+#endif
+
+
+#if defined(MACRO_PREDEF) && !defined(DISABLE_TLS)
+# include "macro_predef.h"
+# ifdef USE_GNUTLS
+#  include "tls-gnu.c"
+# else
+#  include "tls-openssl.c"
+# endif
+#endif
+
+#ifndef MACRO_PREDEF
+
+/* This module is compiled only when it is specifically requested in the
+build-time configuration. However, some compilers don't like compiling empty
+modules, so keep them happy with a dummy when skipping the rest. Make it
+reference itself to stop picky compilers complaining that it is unused, and put
+in a dummy argument to stop even pickier compilers complaining about infinite
+loops. */
+
+#ifdef DISABLE_TLS
+static void dummy(int x) { dummy(x-1); }
+#else
+
+/* Static variables that are used for buffering data by both sets of
+functions and the common functions below.
+
+We're moving away from this; GnuTLS is already using a state, which
+can switch, so we can do TLS callouts during ACLs. */
+
+static const int ssl_xfer_buffer_size = 4096;
+#ifdef USE_OPENSSL
+static uschar *ssl_xfer_buffer = NULL;
+static int ssl_xfer_buffer_lwm = 0;
+static int ssl_xfer_buffer_hwm = 0;
+static int ssl_xfer_eof = FALSE;
+static BOOL ssl_xfer_error = FALSE;
+#endif
+
+
+/*************************************************
+*       Expand string; give error on failure     *
+*************************************************/
+
+/* If expansion is forced to fail, set the result NULL and return TRUE.
+Other failures return FALSE. For a server, an SMTP response is given.
+
+Arguments:
+  s         the string to expand; if NULL just return TRUE
+  name      name of string being expanded (for error)
+  result    where to put the result
+
+Returns:    TRUE if OK; result may still be NULL after forced failure
+*/
+
+static BOOL
+expand_check(const uschar *s, const uschar *name, uschar **result, uschar ** errstr)
+{
+if (!s)
+  *result = NULL;
+else if (  !(*result = expand_string(US s)) /* need to clean up const more */
+	&& !f.expand_string_forcedfail
+	)
+  {
+  *errstr = US"Internal error";
+  log_write(0, LOG_MAIN|LOG_PANIC, "expansion of %s failed: %s", name,
+    expand_string_message);
+  return FALSE;
+  }
+return TRUE;
+}
+
+
+/*************************************************
+*        Timezone environment flipping           *
+*************************************************/
+
+static uschar *
+to_tz(uschar * tz)
+{
+uschar * old = US getenv("TZ");
+(void) setenv("TZ", CCS tz, 1);
+tzset();
+return old;
+}
+
+static void
+restore_tz(uschar * tz)
+{
+if (tz)
+  (void) setenv("TZ", CCS tz, 1);
+else
+  (void) os_unsetenv(US"TZ");
+tzset();
+}
+
+/*************************************************
+*        Many functions are package-specific     *
+*************************************************/
+
+#ifdef USE_GNUTLS
+# include "tls-gnu.c"
+# include "tlscert-gnu.c"
+# define ssl_xfer_buffer (state_server.xfer_buffer)
+# define ssl_xfer_buffer_lwm (state_server.xfer_buffer_lwm)
+# define ssl_xfer_buffer_hwm (state_server.xfer_buffer_hwm)
+# define ssl_xfer_eof (state_server.xfer_eof)
+# define ssl_xfer_error (state_server.xfer_error)
+#endif
+
+#ifdef USE_OPENSSL
+# include "tls-openssl.c"
+# include "tlscert-openssl.c"
+#endif
+
+
+
+/*************************************************
+*           TLS version of ungetc                *
+*************************************************/
+
+/* Puts a character back in the input buffer. Only ever
+called once.
+Only used by the server-side TLS.
+
+Arguments:
+  ch           the character
+
+Returns:       the character
+*/
+
+int
+tls_ungetc(int ch)
+{
+if (ssl_xfer_buffer_lwm <= 0)
+  log_write(0, LOG_MAIN|LOG_PANIC_DIE, "buffer underflow in tls_ungetc");
+
+ssl_xfer_buffer[--ssl_xfer_buffer_lwm] = ch;
+return ch;
+}
+
+
+
+/*************************************************
+*           TLS version of feof                  *
+*************************************************/
+
+/* Tests for a previous EOF
+Only used by the server-side TLS.
+
+Arguments:     none
+Returns:       non-zero if the eof flag is set
+*/
+
+int
+tls_feof(void)
+{
+return (int)ssl_xfer_eof;
+}
+
+
+
+/*************************************************
+*              TLS version of ferror             *
+*************************************************/
+
+/* Tests for a previous read error, and returns with errno
+restored to what it was when the error was detected.
+Only used by the server-side TLS.
+
+>>>>> Hmm. Errno not handled yet. Where do we get it from?  >>>>>
+
+Arguments:     none
+Returns:       non-zero if the error flag is set
+*/
+
+int
+tls_ferror(void)
+{
+return (int)ssl_xfer_error;
+}
+
+
+/*************************************************
+*           TLS version of smtp_buffered         *
+*************************************************/
+
+/* Tests for unused chars in the TLS input buffer.
+Only used by the server-side TLS.
+
+Arguments:     none
+Returns:       TRUE/FALSE
+*/
+
+BOOL
+tls_smtp_buffered(void)
+{
+return ssl_xfer_buffer_lwm < ssl_xfer_buffer_hwm;
+}
+
+
+#endif  /*DISABLE_TLS*/
+
+void
+tls_modify_variables(tls_support * dest_tsp)
+{
+modify_variable(US"tls_bits",                 &dest_tsp->bits);
+modify_variable(US"tls_certificate_verified", &dest_tsp->certificate_verified);
+modify_variable(US"tls_cipher",               &dest_tsp->cipher);
+modify_variable(US"tls_peerdn",               &dest_tsp->peerdn);
+#ifdef USE_OPENSSL
+modify_variable(US"tls_sni",                  &dest_tsp->sni);
+#endif
+}
+
+
+#ifndef DISABLE_TLS
+/************************************************
+*	TLS certificate name operations         *
+************************************************/
+
+/* Convert an rfc4514 DN to an exim comma-sep list.
+Backslashed commas need to be replaced by doublecomma
+for Exim's list quoting.  We modify the given string
+inplace.
+*/
+
+static void
+dn_to_list(uschar * dn)
+{
+for (uschar * cp = dn; *cp; cp++)
+  if (cp[0] == '\\' && cp[1] == ',')
+    *cp++ = ',';
+}
+
+
+/* Extract fields of a given type from an RFC4514-
+format Distinguished Name.  Return an Exim list.
+NOTE: We modify the supplied dn string during operation.
+
+Arguments:
+	dn	Distinguished Name string
+	mod	list containing optional output list-sep and
+		field selector match, comma-separated
+Return:
+	allocated string with list of matching fields,
+	field type stripped
+*/
+
+uschar *
+tls_field_from_dn(uschar * dn, const uschar * mod)
+{
+int insep = ',';
+uschar outsep = '\n';
+uschar * ele;
+uschar * match = NULL;
+int len;
+gstring * list = NULL;
+
+while ((ele = string_nextinlist(&mod, &insep, NULL, 0)))
+  if (ele[0] != '>')
+    match = ele;	/* field tag to match */
+  else if (ele[1])
+    outsep = ele[1];	/* nondefault output separator */
+
+dn_to_list(dn);
+insep = ',';
+len = match ? Ustrlen(match) : -1;
+while ((ele = string_nextinlist(CUSS &dn, &insep, NULL, 0)))
+  if (  !match
+     || Ustrncmp(ele, match, len) == 0 && ele[len] == '='
+     )
+    list = string_append_listele(list, outsep, ele+len+1);
+return string_from_gstring(list);
+}
+
+
+/* Compare a domain name with a possibly-wildcarded name. Wildcards
+are restricted to a single one, as the first element of patterns
+having at least three dot-separated elements.  Case-independent.
+Return TRUE for a match
+*/
+static BOOL
+is_name_match(const uschar * name, const uschar * pat)
+{
+uschar * cp;
+return *pat == '*'		/* possible wildcard match */
+  ?    *++pat == '.'		/* starts star, dot              */
+    && !Ustrchr(++pat, '*')	/* has no more stars             */
+    && Ustrchr(pat, '.')	/* and has another dot.          */
+    && (cp = Ustrchr(name, '.'))/* The name has at least one dot */
+    && strcmpic(++cp, pat) == 0 /* and we only compare after it. */
+  :    !Ustrchr(pat+1, '*')
+    && strcmpic(name, pat) == 0;
+}
+
+/* Compare a list of names with the dnsname elements
+of the Subject Alternate Name, if any, and the
+Subject otherwise.
+
+Arguments:
+	namelist names to compare
+	cert	 certificate
+
+Returns:
+	TRUE/FALSE
+*/
+
+BOOL
+tls_is_name_for_cert(const uschar * namelist, void * cert)
+{
+uschar * altnames = tls_cert_subject_altname(cert, US"dns");
+uschar * subjdn;
+uschar * certname;
+int cmp_sep = 0;
+uschar * cmpname;
+
+if ((altnames = tls_cert_subject_altname(cert, US"dns")))
+  {
+  int alt_sep = '\n';
+  while ((cmpname = string_nextinlist(&namelist, &cmp_sep, NULL, 0)))
+    {
+    const uschar * an = altnames;
+    while ((certname = string_nextinlist(&an, &alt_sep, NULL, 0)))
+      if (is_name_match(cmpname, certname))
+	return TRUE;
+    }
+  }
+
+else if ((subjdn = tls_cert_subject(cert, NULL)))
+  {
+  int sn_sep = ',';
+
+  dn_to_list(subjdn);
+  while ((cmpname = string_nextinlist(&namelist, &cmp_sep, NULL, 0)))
+    {
+    const uschar * sn = subjdn;
+    while ((certname = string_nextinlist(&sn, &sn_sep, NULL, 0)))
+      if (  *certname++ == 'C'
+	 && *certname++ == 'N'
+	 && *certname++ == '='
+	 && is_name_match(cmpname, certname)
+	 )
+	return TRUE;
+    }
+  }
+return FALSE;
+}
+
+
+/* Environment cleanup: The GnuTLS library uses SSLKEYLOGFILE in the environment
+and writes a file by that name.  Our OpenSSL code does the same, using keying
+info from the library API.
+The GnuTLS support only works if exim is run by root, not taking advantage of
+the setuid bit.
+You can use either the external environment (modulo the keep_environment config)
+or the add_environment config option for SSLKEYLOGFILE; the latter takes
+precedence.
+
+If the path is absolute, require it starts with the spooldir; otherwise delete
+the env variable.  If relative, prefix the spooldir.
+*/
+void
+tls_clean_env(void)
+{
+uschar * path = US getenv("SSLKEYLOGFILE");
+if (path)
+  if (!*path)
+    unsetenv("SSLKEYLOGFILE");
+  else if (*path != '/')
+    {
+    DEBUG(D_tls)
+      debug_printf("prepending spooldir to  env SSLKEYLOGFILE\n");
+    setenv("SSLKEYLOGFILE", CCS string_sprintf("%s/%s", spool_directory, path), 1);
+    }
+  else if (Ustrncmp(path, spool_directory, Ustrlen(spool_directory)) != 0)
+    {
+    DEBUG(D_tls)
+      debug_printf("removing env SSLKEYLOGFILE=%s: not under spooldir\n", path);
+    unsetenv("SSLKEYLOGFILE");
+    }
+}
+
+/*************************************************
+*       Drop privs for checking TLS config      *
+*************************************************/
+
+/* We want to validate TLS options during readconf, but do not want to be
+root when we call into the TLS library, in case of library linkage errors
+which cause segfaults; before this check, those were always done as the Exim
+runtime user and it makes sense to continue with that.
+
+Assumes:  tls_require_ciphers has been set, if it will be
+          exim_user has been set, if it will be
+          exim_group has been set, if it will be
+
+Returns:  bool for "okay"; false will cause caller to immediately exit.
+*/
+
+BOOL
+tls_dropprivs_validate_require_cipher(BOOL nowarn)
+{
+const uschar *errmsg;
+pid_t pid;
+int rc, status;
+void (*oldsignal)(int);
+
+/* If TLS will never be used, no point checking ciphers */
+
+if (  !tls_advertise_hosts
+   || !*tls_advertise_hosts
+   || Ustrcmp(tls_advertise_hosts, ":") == 0
+   )
+  return TRUE;
+else if (!nowarn && !tls_certificate)
+  log_write(0, LOG_MAIN,
+    "Warning: No server certificate defined; will use a selfsigned one.\n"
+    " Suggested action: either install a certificate or change tls_advertise_hosts option");
+
+oldsignal = signal(SIGCHLD, SIG_DFL);
+
+fflush(NULL);
+if ((pid = exim_fork(US"cipher-validate")) < 0)
+  log_write(0, LOG_MAIN|LOG_PANIC_DIE, "fork failed for TLS check");
+
+if (pid == 0)
+  {
+  /* in some modes, will have dropped privilege already */
+  if (!geteuid())
+    exim_setugid(exim_uid, exim_gid, FALSE,
+        US"calling tls_validate_require_cipher");
+
+  if ((errmsg = tls_validate_require_cipher()))
+    log_write(0, LOG_PANIC_DIE|LOG_CONFIG,
+        "tls_require_ciphers invalid: %s", errmsg);
+  fflush(NULL);
+  exim_underbar_exit(EXIT_SUCCESS);
+  }
+
+do {
+  rc = waitpid(pid, &status, 0);
+} while (rc < 0 && errno == EINTR);
+
+DEBUG(D_tls)
+  debug_printf("tls_validate_require_cipher child %d ended: status=0x%x\n",
+      (int)pid, status);
+
+signal(SIGCHLD, oldsignal);
+
+return status == 0;
+}
+
+
+
+
+#endif	/*!DISABLE_TLS*/
+#endif	/*!MACRO_PREDEF*/
+
+/* vi: aw ai sw=2
+*/
+/* End of tls.c */