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tls.c
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tls.c
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/* tls.c - STARTTLS helper functions for imapd
* Tim Martin
* 9/21/99
*
* Based upon Lutz Jaenicke's TLS patches for postfix
*
* Copyright (c) 1994-2008 Carnegie Mellon University. All rights reserved.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions
* are met:
*
* 1. Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
*
* 2. Redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in
* the documentation and/or other materials provided with the
* distribution.
*
* 3. The name "Carnegie Mellon University" must not be used to
* endorse or promote products derived from this software without
* prior written permission. For permission or any legal
* details, please contact
* Carnegie Mellon University
* Center for Technology Transfer and Enterprise Creation
* 4615 Forbes Avenue
* Suite 302
* Pittsburgh, PA 15213
* (412) 268-7393, fax: (412) 268-7395
* innovation@andrew.cmu.edu
*
* 4. Redistributions of any form whatsoever must retain the following
* acknowledgment:
* "This product includes software developed by Computing Services
* at Carnegie Mellon University (http://www.cmu.edu/computing/)."
*
* CARNEGIE MELLON UNIVERSITY DISCLAIMS ALL WARRANTIES WITH REGARD TO
* THIS SOFTWARE, INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY
* AND FITNESS, IN NO EVENT SHALL CARNEGIE MELLON UNIVERSITY BE LIABLE
* FOR ANY SPECIAL, INDIRECT OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
* WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN
* AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING
* OUT OF OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
*/
/*
* NAME
* tls
* SUMMARY
* interface to openssl routines
* SYNOPSIS
* #include <tls.h>
*
* DESCRIPTION
* This module is the interface between Cyrus Imapd and the OpenSSL library.
* As of now only one filedescriptor can be handled, so only one
* TLS channel can be open at a time.
*
* tls_init_serverengine() is called once when the server is started
* in order to initialize as much of the TLS stuff as possible.
* The certificate handling is also decided during the setup phase,
* so that a peer specific handling is not possible.
*
* tls_start_servertls() activates the TLS feature for the
* filedescriptor selected with tls_setfd() before. We expect
* that all buffers are flushed and the TLS handshake can begin
* immediately.
*
* tls_stop_servertls() sends the "close notify" alert via
* SSL_shutdown() to the peer and resets all connection specific
* TLS data. As RFC2487 does not specify a separate shutdown, it
* is supposed that the underlying TCP connection is shut down
* immediately afterwards, so we don't care about additional data
* coming through the channel.
*
* Once the TLS connection is initiated, information about the TLS
* state is available:
* tls_protocol holds the protocol name (SSLv2, SSLv3, TLSv1),
* tls_cipher_name the cipher name (e.g. RC4/MD5),
* tls_cipher_usebits the number of bits actually used (e.g. 40),
* tls_cipher_algbits the number of bits the algorithm is based on
* (e.g. 128).
* The last two values may be different when talking to a crippled
* - ahem - export controled peer (e.g. 40/128).
*
* xxx we need to offer a callback to do peer issuer certification.
* data that should be available for inspection:
* If the peer offered a certifcate _and_ the certificate could be
* verified successfully, part of the certificate data are available as:
* tls_peer_subject X509v3-oneline with the DN of the peer
* pfixlts_peer_CN extracted CommonName of the peer
* tls_peer_issuer X509v3-oneline with the DN of the issuer
* pfixlts_peer_CN extracted CommonName of the issuer
* tls_peer_fingerprint fingerprint of the certificate
*
*/
#include <config.h>
#ifdef HAVE_SSL
/* System library. */
#include <sys/types.h>
#include <unistd.h>
#include <stdio.h>
#include <string.h>
#include <syslog.h>
/* OpenSSL library. */
#include <openssl/lhash.h>
#include <openssl/bn.h>
#include <openssl/err.h>
#include <openssl/pem.h>
#include <openssl/x509.h>
#include <openssl/ssl.h>
/* Application-specific. */
#include "assert.h"
#include "nonblock.h"
#include "xmalloc.h"
#include "tls.h"
#include "tls_th-lock.h"
/* Session caching/reuse stuff */
#include "global.h"
#include "cyrusdb.h"
#define DB (config_tls_sessions_db) /* sessions are binary -> MUST use DB3 */
static struct db *sessdb = NULL;
static int sess_dbopen = 0;
enum {
var_imapd_tls_loglevel = 0,
var_proxy_tls_loglevel = 0,
CCERT_BUFSIZ = 256
};
static int verify_depth = 5;
static int verify_error = X509_V_OK;
static SSL_CTX *s_ctx = NULL, *c_ctx = NULL;
static int tls_serverengine = 0; /* server engine initialized? */
static int tls_clientengine = 0; /* client engine initialized? */
static int do_dump = 0; /* actively dumping protocol? */
EXPORTED int tls_enabled(void)
{
const char *val;
val = config_getstring(IMAPOPT_TLS_SERVER_CERT);
if (!val || !strcasecmp(val, "disabled")) return 0;
val = config_getstring(IMAPOPT_TLS_SERVER_KEY);
if (!val || !strcasecmp(val, "disabled")) return 0;
if (config_getswitch(IMAPOPT_CHATTY))
syslog(LOG_INFO, "TLS is available.");
return 1;
}
/* taken from OpenSSL apps/s_cb.c
* tim - this seems to just be giving logging messages
*/
static void apps_ssl_info_callback(const SSL * s, int where, int ret)
{
char *str;
int w;
if (var_imapd_tls_loglevel==0) return;
w = where & ~SSL_ST_MASK;
if (w & SSL_ST_CONNECT)
str = "SSL_connect";
else if (w & SSL_ST_ACCEPT)
str = "SSL_accept";
else
str = "undefined";
if (where & SSL_CB_LOOP) {
if (tls_serverengine && (var_imapd_tls_loglevel >= 2))
syslog(LOG_DEBUG, "%s:%s", str, SSL_state_string_long(s));
} else if (where & SSL_CB_ALERT) {
str = (where & SSL_CB_READ) ? "read" : "write";
if ((tls_serverengine && (var_imapd_tls_loglevel >= 2)) ||
((ret & 0xff) != SSL3_AD_CLOSE_NOTIFY))
syslog(LOG_DEBUG, "SSL3 alert %s:%s:%s", str,
SSL_alert_type_string_long(ret),
SSL_alert_desc_string_long(ret));
} else if (where & SSL_CB_EXIT) {
if (ret == 0)
syslog(LOG_DEBUG, "%s:failed in %s",
str, SSL_state_string_long(s));
else if (ret < 0) {
syslog(LOG_DEBUG, "%s:error in %s",
str, SSL_state_string_long(s));
}
}
}
#if OPENSSL_VERSION_NUMBER < 0x10100000L
/* taken from OpenSSL apps/s_cb.c
not thread safe! */
static RSA *tmp_rsa_cb(SSL * s __attribute__((unused)),
int export __attribute__((unused)),
int keylength)
{
static RSA *rsa_tmp = NULL;
if (rsa_tmp == NULL) {
rsa_tmp = RSA_generate_key(keylength, RSA_F4, NULL, NULL);
}
return (rsa_tmp);
}
#endif
#if OPENSSL_VERSION_NUMBER < 0x10100000L
/* replacements for new 1.1 API accessors */
/* XXX probably put these somewhere central */
static int DH_set0_pqg(DH *dh, BIGNUM *p, BIGNUM *q, BIGNUM *g)
{
if (p == NULL || g == NULL) return 0;
dh->p = p;
dh->q = q; /* optional */
dh->g = g;
return 1;
}
#endif
#if (OPENSSL_VERSION_NUMBER >= 0x0090800fL)
/* Logic copied from OpenSSL apps/s_server.c: give the TLS context
* DH params to work with DHE-* cipher suites. Hardcoded fallback
* in case no DH params in server_key or server_cert.
* Modified quite a bit for openssl 1.1.0 compatibility.
* XXX we might be able to just replace this with DH_get_1024_160?
* XXX the apps/s_server.c example doesn't use this anymore at all.
*/
static DH *get_dh1024(void)
{
/* Second Oakley group 1024-bits MODP group from RFC2409 */
DH *dh;
BIGNUM *p = NULL, *g = NULL;
dh = DH_new();
if (!dh) return NULL;
p = get_rfc2409_prime_1024(NULL);
BN_dec2bn(&g, "2");
if (DH_set0_pqg(dh, p, NULL, g))
return dh;
if (g) BN_free(g);
if (p) BN_free(p);
DH_free(dh);
return NULL;
}
static DH *load_dh_param(const char *keyfile, const char *certfile)
{
DH *ret=NULL;
BIO *bio = NULL;
if (keyfile) bio = BIO_new_file(keyfile, "r");
if ((bio == NULL) && certfile) bio = BIO_new_file(certfile,"r");
if (bio) ret=PEM_read_bio_DHparams(bio,NULL,NULL,NULL);
if (ret == NULL) {
ret = get_dh1024();
syslog(LOG_NOTICE, "inittls: Loading hard-coded DH parameters");
} else {
syslog(LOG_NOTICE, "inittls: Loading DH parameters from file");
}
if (bio != NULL) BIO_free(bio);
return(ret);
}
#endif /* OPENSSL_VERSION_NUMBER >= 0x009080fL */
/* taken from OpenSSL apps/s_cb.c */
static int verify_callback(int ok, X509_STORE_CTX * ctx)
{
char buf[256];
X509 *err_cert;
int err;
int depth;
syslog(LOG_DEBUG, "Doing a peer verify");
err_cert = X509_STORE_CTX_get_current_cert(ctx);
err = X509_STORE_CTX_get_error(ctx);
depth = X509_STORE_CTX_get_error_depth(ctx);
X509_NAME_oneline(X509_get_subject_name(err_cert), buf, sizeof(buf));
if (ok==0)
{
syslog(LOG_ERR, "verify error:num=%d:%s", err,
X509_verify_cert_error_string(err));
if (verify_depth >= depth) {
ok = 0;
verify_error = X509_V_OK;
} else {
ok = 0;
verify_error = X509_V_ERR_CERT_CHAIN_TOO_LONG;
}
}
switch (err) {
case X509_V_ERR_UNABLE_TO_GET_ISSUER_CERT:
X509_NAME_oneline(X509_get_issuer_name(err_cert), buf, sizeof(buf));
syslog(LOG_NOTICE, "issuer= %s", buf);
break;
case X509_V_ERR_CERT_NOT_YET_VALID:
case X509_V_ERR_ERROR_IN_CERT_NOT_BEFORE_FIELD:
syslog(LOG_NOTICE, "cert not yet valid");
break;
case X509_V_ERR_CERT_HAS_EXPIRED:
case X509_V_ERR_ERROR_IN_CERT_NOT_AFTER_FIELD:
syslog(LOG_NOTICE, "cert has expired");
break;
}
return (ok);
}
#if (OPENSSL_VERSION_NUMBER >= 0x0090806fL)
static int servername_callback(SSL *ssl, int *ad __attribute__((unused)),
void *arg __attribute__((unused)))
{
const char *servername = SSL_get_servername(ssl, TLSEXT_NAMETYPE_host_name);
if (servername) {
syslog(LOG_DEBUG, "TLS Server Name Indication (SNI) Extension: \"%s\"",
servername);
}
return SSL_TLSEXT_ERR_OK;
}
#endif
/*
* taken from OpenSSL crypto/bio/b_dump.c, modified to save a lot of strcpy
* and strcat by Matti Aarnio.
*/
#define TRUNCATE
#define DUMP_WIDTH 16
static int tls_dump(const char *s, int len)
{
int ret = 0;
char buf[160 + 1];
char *ss;
int i;
int j;
int rows;
int trunc;
unsigned char ch;
trunc = 0;
#ifdef TRUNCATE
for (; (len > 0) && ((s[len - 1] == ' ') || (s[len - 1] == '\0')); len--)
trunc++;
#endif
rows = (len / DUMP_WIDTH);
if ((rows * DUMP_WIDTH) < len)
rows++;
for (i = 0; i < rows; i++) {
unsigned int val;
buf[0] = '\0'; /* start with empty string */
ss = buf;
val = i * DUMP_WIDTH;
assert(val <= 0xFFFF);
sprintf(ss, "%04x ", i * DUMP_WIDTH);
ss += strlen(ss);
for (j = 0; j < DUMP_WIDTH; j++) {
if (((i * DUMP_WIDTH) + j) >= len) {
strcpy(ss, " ");
} else {
ch = ((unsigned char) *((char *) (s) + i * DUMP_WIDTH + j))
& 0xFF;
sprintf(ss, "%02x%c", ch, j == 7 ? '|' : ' ');
ss += 3;
}
}
ss += strlen(ss);
*ss+= ' ';
for (j = 0; j < DUMP_WIDTH; j++) {
if (((i * DUMP_WIDTH) + j) >= len)
break;
ch = ((unsigned char) *((char *) (s) + i * DUMP_WIDTH + j)) & 0xff;
*ss+= (((ch >= ' ') && (ch <= '~')) ? ch : '.');
if (j == 7) *ss+= ' ';
}
*ss = 0;
/*
* if this is the last call then update the ddt_dump thing so that
* we will move the selection point in the debug window
*/
if (var_imapd_tls_loglevel>0)
syslog(LOG_DEBUG, "%s", buf);
ret += strlen(buf);
}
#ifdef TRUNCATE
if (trunc > 0) {
snprintf(buf, sizeof(buf), "%04x - <SPACES/NULS>\n", len+ trunc);
if (var_imapd_tls_loglevel>0)
syslog(LOG_DEBUG, "%s", buf);
ret += strlen(buf);
}
#endif
return (ret);
}
/*
* Set up the cert things on the server side. We do need both the
* private key (in key_file) and the cert (in cert_file).
* Both files may be identical.
*
* This function is taken from OpenSSL apps/s_cb.c
*/
static int set_cert_stuff(SSL_CTX * ctx,
const char *cert_file, const char *key_file)
{
if (cert_file != NULL) {
/* SSL_CTX_use_certificate_chain_file() requires an empty error stack.
* To make sure there is no error from previous op, we clear it here...
*/
ERR_clear_error();
if (SSL_CTX_use_certificate_chain_file(ctx, cert_file) <= 0) {
syslog(LOG_ERR, "unable to get certificate from '%s'", cert_file);
return (0);
}
if (key_file == NULL)
key_file = cert_file;
if (SSL_CTX_use_PrivateKey_file(ctx, key_file,
SSL_FILETYPE_PEM) <= 0) {
syslog(LOG_ERR, "unable to get private key from '%s'", key_file);
return (0);
}
/* Now we know that a key and cert have been set against
* the SSL context */
if (!SSL_CTX_check_private_key(ctx)) {
syslog(
LOG_ERR,
"Private key '%s' does not match public key '%s'",
cert_file,
key_file
);
return (0);
}
}
return (1);
}
/*
* The new_session_cb() is called, whenever a new session has been
* negotiated and session caching is enabled. We save the session in
* a database so that we can share sessions between processes.
*/
static int new_session_cb(SSL *ssl __attribute__((unused)),
SSL_SESSION *sess)
{
int len;
unsigned char *data = NULL;
time_t expire;
int ret = -1;
unsigned char *asn;
const unsigned char *session_id = NULL;
unsigned int session_id_length = 0;
assert(sess);
if (!sess_dbopen) return 0;
/* find the size of the ASN1 representation of the session */
len = i2d_SSL_SESSION(sess, NULL);
/*
* create the data buffer. the data is stored as:
* <expire time><ASN1 data>
*/
data = (unsigned char *) xmalloc(sizeof(time_t)+len*sizeof(unsigned char));
/* transform the session into its ASN1 representation */
asn = data + sizeof(time_t);
len = i2d_SSL_SESSION(sess, &asn);
if (!len) syslog(LOG_ERR, "i2d_SSL_SESSION failed");
/* set the expire time for the external cache, and prepend it to data */
expire = SSL_SESSION_get_time(sess) + SSL_SESSION_get_timeout(sess);
memcpy(data, &expire, sizeof(time_t));
if (len) {
/* store the session in our database */
session_id = SSL_SESSION_get_id(sess, &session_id_length);
if (session_id_length) {
do {
ret = cyrusdb_store(sessdb, (const char *) session_id,
session_id_length,
(const char *) data, len + sizeof(time_t), NULL);
} while (ret == CYRUSDB_AGAIN);
}
}
free(data);
/* log this transaction */
if (var_imapd_tls_loglevel > 0) {
unsigned int i;
char idstr[SSL_MAX_SSL_SESSION_ID_LENGTH*2 + 1];
for (i = 0; i < session_id_length; i++) {
sprintf(idstr+i*2, "%02X", session_id[i]);
}
syslog(LOG_DEBUG, "new TLS session: id=%s, expire=%s, status=%s",
idstr, ctime(&expire), ret ? "failed" : "ok");
}
return (ret == 0);
}
/*
* Function for removing a session from our database.
*/
static void remove_session(const unsigned char *id, int idlen)
{
int ret;
assert(id);
assert(idlen <= SSL_MAX_SSL_SESSION_ID_LENGTH);
if (!idlen) return;
if (!sess_dbopen) return;
do {
ret = cyrusdb_delete(sessdb, (const char *) id, idlen, NULL, 1);
} while (ret == CYRUSDB_AGAIN);
/* log this transaction */
if (var_imapd_tls_loglevel > 0) {
char idstr[SSL_MAX_SSL_SESSION_ID_LENGTH*2 + 1];
bin_to_hex(id, idlen, idstr, BH_UPPER);
syslog(LOG_DEBUG, "remove TLS session: id=%s", idstr);
}
}
/*
* The remove_session_cb() is called, whenever the SSL engine removes
* a session from the internal cache. This happens if the session is
* removed because it is expired or when a connection was not shutdown
* cleanly.
*/
static void remove_session_cb(SSL_CTX *ctx __attribute__((unused)),
SSL_SESSION *sess)
{
const unsigned char *session_id = NULL;
unsigned int session_id_length = 0;
assert(sess);
session_id = SSL_SESSION_get_id(sess, &session_id_length);
remove_session(session_id, session_id_length);
}
/*
* The get_session_cb() is only called on SSL/TLS servers with the
* session id proposed by the client. The get_session_cb() is always
* called, also when session caching was disabled. We lookup the
* session in our database in case it was stored by another process.
*/
#if OPENSSL_VERSION_NUMBER >= 0x10100000L
static SSL_SESSION *get_session_cb(SSL *ssl __attribute__((unused)),
const unsigned char *id, int idlen, int *copy)
#else
static SSL_SESSION *get_session_cb(SSL *ssl __attribute__((unused)),
unsigned char *id, int idlen, int *copy)
#endif
{
int ret;
const char *data = NULL;
size_t len = 0;
time_t expire = 0, now = time(0);
SSL_SESSION *sess = NULL;
assert(id);
assert(idlen <= SSL_MAX_SSL_SESSION_ID_LENGTH);
if (!sess_dbopen) return NULL;
do {
ret = cyrusdb_fetch(sessdb, (const char *) id, idlen, &data, &len, NULL);
} while (ret == CYRUSDB_AGAIN);
if (!ret && data) {
assert(len >= (int) sizeof(time_t));
/* grab the expire time */
memcpy(&expire, data, sizeof(time_t));
/* check if the session has expired */
if (expire < now) {
remove_session(id, idlen);
}
else {
/* transform the ASN1 representation of the session
into an SSL_SESSION object */
const unsigned char *asn = (unsigned char *) data + sizeof(time_t);
sess = d2i_SSL_SESSION(NULL, &asn, len - sizeof(time_t));
if (!sess) syslog(LOG_ERR, "d2i_SSL_SESSION failed: %m");
}
}
/* log this transaction */
if (var_imapd_tls_loglevel > 0) {
int i;
char idstr[SSL_MAX_SSL_SESSION_ID_LENGTH*2 + 1];
for (i = 0; i < idlen; i++)
sprintf(idstr+i*2, "%02X", id[i]);
syslog(LOG_DEBUG, "get TLS session: id=%s, expire=%s, status=%s",
idstr, ctime(&expire),
!data ? "not found" : expire < now ? "expired" : "ok");
}
*copy = 0;
return sess;
}
/*
* Seed the random number generator.
*/
static int tls_rand_init(void)
{
#ifdef EGD_SOCKET
return (RAND_egd(EGD_SOCKET));
#else
/* otherwise let OpenSSL do it internally */
return 0;
#endif
}
/*
* This is the setup routine for the SSL server. As smtpd might be called
* more than once, we only want to do the initialization one time.
*
* The skeleton of this function is taken from OpenSSL apps/s_server.c.
* returns -1 on error
*/
/* must be called after cyrus_init */
// I am the server
EXPORTED int tls_init_serverengine(const char *ident,
int verifydepth,
int askcert)
{
int off = 0;
int verify_flags = SSL_VERIFY_NONE;
const char *cipher_list;
const char *client_ca_dir;
const char *client_ca_file;
const char *server_ca_file;
const char *server_cert_file;
const char *server_key_file;
enum enum_value tls_client_certs;
int server_cipher_order;
int timeout;
/* Whether or not to use any client certificate CA context to
* verify client SSL certificates with.
*
* This is initially switched off by a value of "off" for the
* tls_client_certs setting, or should no client_ca_dir nor
* client_ca_file be specified. */
int use_client_certs = 1;
if (tls_serverengine)
return (0); /* already running */
if (var_imapd_tls_loglevel >= 2)
syslog(LOG_DEBUG, "starting TLS server engine");
SSL_library_init();
SSL_load_error_strings();
if (tls_rand_init() == -1) {
syslog(LOG_ERR,"TLS server engine: cannot seed PRNG");
return -1;
}
#if (OPENSSL_VERSION_NUMBER >= 0x10100000L)
s_ctx = SSL_CTX_new(TLS_server_method());
#else
s_ctx = SSL_CTX_new(SSLv23_server_method());
#endif
if (s_ctx == NULL) {
return (-1);
};
off |= SSL_OP_ALL; /* Work around all known bugs */
off |= SSL_OP_NO_SSLv2; /* Disable insecure SSLv2 */
off |= SSL_OP_NO_SSLv3; /* Disable insecure SSLv3 */
off |= SSL_OP_NO_COMPRESSION; /* Disable TLS compression */
const char *tls_versions = config_getstring(IMAPOPT_TLS_VERSIONS);
if (strstr(tls_versions, "tls1_2") == NULL) {
#if (OPENSSL_VERSION_NUMBER >= 0x1000105fL)
//syslog(LOG_DEBUG, "TLS server engine: Disabled TLSv1.2");
off |= SSL_OP_NO_TLSv1_2;
#else
syslog(LOG_ERR, "ERROR: TLSv1.2 configured, OpenSSL < 1.0.1e insufficient");
#endif // (OPENSSL_VERSION_NUMBER >= 0x1000105fL)
}
if (strstr(tls_versions, "tls1_1") == NULL) {
#if (OPENSSL_VERSION_NUMBER >= 0x1000000fL)
//syslog(LOG_DEBUG, "TLS server engine: Disabled TLSv1.1");
off |= SSL_OP_NO_TLSv1_1;
#else
syslog(LOG_ERR, "ERROR: TLSv1.1 configured, OpenSSL < 1.0.0 insufficient");
#endif // (OPENSSL_VERSION_NUMBER >= 0x1000000fL)
}
if (strstr(tls_versions, "tls1_0") == NULL) {
//syslog(LOG_DEBUG, "TLS server engine: Disabled TLSv1.0");
off |= SSL_OP_NO_TLSv1;
}
server_cipher_order = config_getswitch(IMAPOPT_TLS_PREFER_SERVER_CIPHERS);
if (server_cipher_order)
off |= SSL_OP_CIPHER_SERVER_PREFERENCE;
SSL_CTX_set_options(s_ctx, off);
SSL_CTX_set_info_callback(s_ctx, apps_ssl_info_callback);
cipher_list = config_getstring(IMAPOPT_TLS_CIPHERS);
if (!SSL_CTX_set_cipher_list(s_ctx, cipher_list)) {
syslog(
LOG_ERR,
"TLS server engine: cannot load cipher list '%s'",
cipher_list
);
return (-1);
}
tls_client_certs = config_getenum(IMAPOPT_TLS_CLIENT_CERTS);
if (tls_client_certs != IMAP_ENUM_TLS_CLIENT_CERTS_OFF) {
// The use of client certificates for authentication is
// optional or required.
client_ca_dir = config_getstring(IMAPOPT_TLS_CLIENT_CA_DIR);
client_ca_file = config_getstring(IMAPOPT_TLS_CLIENT_CA_FILE);
if (config_debug) {
syslog(
LOG_DEBUG, "tls_client_ca_dir=%s tls_client_ca_file=%s",
IS_NULL(client_ca_dir), IS_NULL(client_ca_file)
);
}
if (client_ca_dir || client_ca_file) {
// Attempt to load client_ca_dir and/or client_ca_file
if ((!SSL_CTX_load_verify_locations(s_ctx, client_ca_file, client_ca_dir)) ||
(!SSL_CTX_set_default_verify_paths(s_ctx))) {
// Just a warning since this is only necessary for client auth.
syslog(
LOG_WARNING,
"TLS server engine: Failed loading client CA data, cert auth disabled."
);
use_client_certs = 0;
}
} else { // (client_ca_dir || client_ca_file)
// We have no CA to verify client certificates against.
syslog(LOG_DEBUG, "TLS server engine: No client CA data configured.");
// This is fatal should client certificates be required.
if (tls_client_certs == IMAP_ENUM_TLS_CLIENT_CERTS_REQUIRE) {
return (-1);
}
use_client_certs = 0;
}
} else { // (tls_client_certs != IMAP_ENUM_TLS_CLIENT_CERTS_OFF)
// The use of client certificates is turned off.
use_client_certs = 0;
}
server_ca_file = config_getstring(IMAPOPT_TLS_SERVER_CA_FILE);
server_cert_file = config_getstring(IMAPOPT_TLS_SERVER_CERT);
server_key_file = config_getstring(IMAPOPT_TLS_SERVER_KEY);
if (config_debug) {
syslog(
LOG_DEBUG, "tls_server_cert=%s tls_server_key=%s",
IS_NULL(server_cert_file), IS_NULL(server_key_file)
);
}
/* Only consider adding additional CA certificates -used to verify certificates
* issued to clients, which may have been issued by an intermediate CA and
* not the CA that issued our server certificate- when indeed we are using
* SSL/TLS on this server.
*/
if (server_ca_file && !strcasecmp(server_cert_file, "disabled")) {
SSL_CTX_set_mode(s_ctx,SSL_CTX_get_mode(s_ctx) | SSL_MODE_NO_AUTO_CHAIN);
BIO *filebio = BIO_new_file(server_ca_file, "r");
if (filebio) {
X509 *cacert;
syslog(
LOG_DEBUG,
"TLS server engine: loading additional client CA information from file %s",
server_ca_file
);
while ((cacert = PEM_read_bio_X509(filebio,NULL,NULL,NULL)) != NULL) {
char buf[256];
X509_NAME_oneline(X509_get_subject_name(cacert), buf, sizeof(buf));
if (!SSL_CTX_add_extra_chain_cert(s_ctx, cacert)) {
syslog(
LOG_ERR,
"TLS server engine: failed to add client_ca_cert to chain: %s",
buf
);
X509_free(cacert);
} else {
syslog(LOG_DEBUG, "TLS server engine: added CA cert to chain: %s", buf);
}
}
BIO_free(filebio);
} else {
syslog(
LOG_ERR,
"TLS server engine: Cannot load additional client CA information from file %s",
server_ca_file
);
return (-1);
}
}
if (!set_cert_stuff(s_ctx, server_cert_file, server_key_file)) {
syslog(LOG_ERR, "TLS server engine: cannot load cert/key data, may be a cert/key mismatch?");
return (-1);
}
#if OPENSSL_VERSION_NUMBER < 0x10100000L
SSL_CTX_set_tmp_rsa_callback(s_ctx, tmp_rsa_cb);
#endif
#if (OPENSSL_VERSION_NUMBER >= 0x0090800fL)
/* Load DH params for DHE-* key exchanges */
DH* dh_freeme = load_dh_param(server_key_file, server_cert_file);
SSL_CTX_set_tmp_dh(s_ctx, dh_freeme);
#endif
#if (OPENSSL_VERSION_NUMBER >= 0x1000103fL)
const char *ec = config_getstring(IMAPOPT_TLS_ECCURVE);
int openssl_nid = OBJ_sn2nid(ec);
if (openssl_nid != 0) {
EC_KEY *ecdh;
ecdh = EC_KEY_new_by_curve_name(openssl_nid);
if (ecdh != NULL) {
SSL_CTX_set_tmp_ecdh(s_ctx, ecdh);
EC_KEY_free(ecdh);
}
}
#endif
verify_depth = verifydepth;
if (!use_client_certs) {
if ((tls_client_certs == IMAP_ENUM_TLS_CLIENT_CERTS_REQUIRE) && askcert)
syslog(LOG_ERR, "TLS server engine: No client cert CA specified.");
} else {
STACK_OF(X509_NAME) *CAnames = SSL_load_client_CA_file(client_ca_file);
if (!CAnames || sk_X509_NAME_num(CAnames) < 1) {
syslog(
LOG_ERR,
"TLS server engine: No client CA certs specified. Client side certs may not work"
);
} else {
if (askcert || tls_client_certs)
verify_flags = SSL_VERIFY_PEER | SSL_VERIFY_CLIENT_ONCE;
if (tls_client_certs == IMAP_ENUM_TLS_CLIENT_CERTS_REQUIRE)
verify_flags |= SSL_VERIFY_FAIL_IF_NO_PEER_CERT;
SSL_CTX_set_client_CA_list(s_ctx, CAnames);
syslog(
LOG_DEBUG,
"Set client CA list: Client cert %srequested, %srequired",
verify_flags & SSL_VERIFY_PEER ? "" : "not ",
verify_flags & SSL_VERIFY_FAIL_IF_NO_PEER_CERT ? "":"not "
);
}
}
SSL_CTX_set_verify(s_ctx, verify_flags, verify_callback);
#if (OPENSSL_VERSION_NUMBER >= 0x0090806fL)
SSL_CTX_set_tlsext_servername_callback(s_ctx, servername_callback);
#endif
/* Don't use an internal session cache */
SSL_CTX_sess_set_cache_size(s_ctx, 1); /* 0 is unlimited, so use 1 */
SSL_CTX_set_session_cache_mode(s_ctx, SSL_SESS_CACHE_SERVER |
SSL_SESS_CACHE_NO_AUTO_CLEAR |
SSL_SESS_CACHE_NO_INTERNAL_LOOKUP);
/* Get the session timeout from the config file (in minutes) */
timeout = config_getint(IMAPOPT_TLS_SESSION_TIMEOUT);
if (timeout < 0) timeout = 0;
if (timeout > 1440) timeout = 1440; /* 24 hours max */
/* A timeout of zero disables session caching */
if (timeout) {
const char *fname = NULL;
char *tofree = NULL;
int r;
/* Set the context for session reuse -- use the service ident */
SSL_CTX_set_session_id_context(s_ctx, (void*) ident, strlen(ident));
/* Set the timeout for the internal/external cache (in seconds) */
SSL_CTX_set_timeout(s_ctx, timeout*60);
/* Set the callback functions for the external session cache */
SSL_CTX_sess_set_new_cb(s_ctx, new_session_cb);
SSL_CTX_sess_set_remove_cb(s_ctx, remove_session_cb);
SSL_CTX_sess_set_get_cb(s_ctx, get_session_cb);
fname = config_getstring(IMAPOPT_TLS_SESSIONS_DB_PATH);
/* create the name of the db file */
if (!fname) {
tofree = strconcat(config_dir, FNAME_TLSSESSIONS, (char *)NULL);
fname = tofree;
}
r = cyrusdb_open(DB, fname, CYRUSDB_CREATE, &sessdb);
if (r != 0) {
syslog(LOG_ERR, "DBERROR: opening %s: %s",
fname, cyrusdb_strerror(ret));
}
else
sess_dbopen = 1;
free(tofree);
}
tls_serverengine = 1;
#if (OPENSSL_VERSION_NUMBER >= 0x0090800fL)
DH_free(dh_freeme);
#endif
return (0);
}
/* taken from OpenSSL apps/s_cb.c */