From 4eac1dbb5f70a652d31847eec7c28d245f36cdbb Mon Sep 17 00:00:00 2001
From: Martin Sehnoutka <msehnout@redhat.com>
Date: Thu, 17 Nov 2016 10:48:28 +0100
Subject: [PATCH 21/33] Introduce support for DHE based cipher suites.
---
parseconf.c | 1 +
ssl.c | 93 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++-
tunables.c | 5 +++-
tunables.h | 1 +
vsftpd.conf.5 | 6 ++++
5 files changed, 104 insertions(+), 2 deletions(-)
diff --git a/parseconf.c b/parseconf.c
index 3e0dba4..38e3182 100644
--- a/parseconf.c
+++ b/parseconf.c
@@ -176,6 +176,7 @@ parseconf_str_array[] =
{ "email_password_file", &tunable_email_password_file },
{ "rsa_cert_file", &tunable_rsa_cert_file },
{ "dsa_cert_file", &tunable_dsa_cert_file },
+ { "dh_param_file", &tunable_dh_param_file },
{ "ssl_ciphers", &tunable_ssl_ciphers },
{ "rsa_private_key_file", &tunable_rsa_private_key_file },
{ "dsa_private_key_file", &tunable_dsa_private_key_file },
diff --git a/ssl.c b/ssl.c
index c362983..22b69b3 100644
--- a/ssl.c
+++ b/ssl.c
@@ -28,6 +28,8 @@
#include <openssl/err.h>
#include <openssl/rand.h>
#include <openssl/bio.h>
+#include <openssl/dh.h>
+#include <openssl/bn.h>
#include <errno.h>
#include <limits.h>
@@ -38,6 +40,7 @@ static void setup_bio_callbacks();
static long bio_callback(
BIO* p_bio, int oper, const char* p_arg, int argi, long argl, long retval);
static int ssl_verify_callback(int verify_ok, X509_STORE_CTX* p_ctx);
+static DH *ssl_tmp_dh_callback(SSL *ssl, int is_export, int keylength);
static int ssl_cert_digest(
SSL* p_ssl, struct vsf_session* p_sess, struct mystr* p_str);
static void maybe_log_shutdown_state(struct vsf_session* p_sess);
@@ -51,6 +54,60 @@ static int ssl_read_common(struct vsf_session* p_sess,
static int ssl_inited;
static struct mystr debug_str;
+
+// Grab prime number from OpenSSL; <openssl/bn.h>
+// (get_rfc*) for all available primes.
+// wraps selection of comparable algorithm strength
+#if !defined(match_dh_bits)
+ #define match_dh_bits(keylen) \
+ keylen >= 8191 ? 8192 : \
+ keylen >= 6143 ? 6144 : \
+ keylen >= 4095 ? 4096 : \
+ keylen >= 3071 ? 3072 : \
+ keylen >= 2047 ? 2048 : \
+ keylen >= 1535 ? 1536 : \
+ keylen >= 1023 ? 1024 : 768
+#endif
+
+#if !defined(DH_get_prime)
+ BIGNUM *
+ DH_get_prime(int bits)
+ {
+ switch (bits) {
+ case 768: return get_rfc2409_prime_768(NULL);
+ case 1024: return get_rfc2409_prime_1024(NULL);
+ case 1536: return get_rfc3526_prime_1536(NULL);
+ case 2048: return get_rfc3526_prime_2048(NULL);
+ case 3072: return get_rfc3526_prime_3072(NULL);
+ case 4096: return get_rfc3526_prime_4096(NULL);
+ case 6144: return get_rfc3526_prime_6144(NULL);
+ case 8192: return get_rfc3526_prime_8192(NULL);
+ // shouldn't happen when used match_dh_bits; strict compiler
+ default: return NULL;
+ }
+}
+#endif
+
+#if !defined(DH_get_dh)
+ // Grab DH parameters
+ DH *
+ DH_get_dh(int size)
+ {
+ DH *dh = DH_new();
+ if (!dh) {
+ return NULL;
+ }
+ dh->p = DH_get_prime(match_dh_bits(size));
+ BN_dec2bn(&dh->g, "2");
+ if (!dh->p || !dh->g)
+ {
+ DH_free(dh);
+ return NULL;
+ }
+ return dh;
+ }
+#endif
+
void
ssl_init(struct vsf_session* p_sess)
{
@@ -65,7 +122,7 @@ ssl_init(struct vsf_session* p_sess)
{
die("SSL: could not allocate SSL context");
}
- options = SSL_OP_ALL;
+ options = SSL_OP_ALL | SSL_OP_SINGLE_DH_USE;
if (!tunable_sslv2)
{
options |= SSL_OP_NO_SSLv2;
@@ -111,6 +168,25 @@ ssl_init(struct vsf_session* p_sess)
die("SSL: cannot load DSA private key");
}
}
+ if (tunable_dh_param_file)
+ {
+ BIO *bio;
+ DH *dhparams = NULL;
+ if ((bio = BIO_new_file(tunable_dh_param_file, "r")) == NULL)
+ {
+ die("SSL: cannot load custom DH params");
+ }
+ else
+ {
+ dhparams = PEM_read_bio_DHparams(bio, NULL, NULL, NULL);
+ BIO_free(bio);
+
+ if (!SSL_CTX_set_tmp_dh(p_ctx, dhparams))
+ {
+ die("SSL: setting custom DH params failed");
+ }
+ }
+ }
if (tunable_ssl_ciphers &&
SSL_CTX_set_cipher_list(p_ctx, tunable_ssl_ciphers) != 1)
{
@@ -165,6 +241,9 @@ ssl_init(struct vsf_session* p_sess)
/* Ensure cached session doesn't expire */
SSL_CTX_set_timeout(p_ctx, INT_MAX);
}
+
+ SSL_CTX_set_tmp_dh_callback(p_ctx, ssl_tmp_dh_callback);
+
p_sess->p_ssl_ctx = p_ctx;
ssl_inited = 1;
}
@@ -702,6 +781,18 @@ ssl_verify_callback(int verify_ok, X509_STORE_CTX* p_ctx)
return 1;
}
+#define UNUSED(x) ( (void)(x) )
+
+static DH *
+ssl_tmp_dh_callback(SSL *ssl, int is_export, int keylength)
+{
+ // strict compiler bypassing
+ UNUSED(ssl);
+ UNUSED(is_export);
+
+ return DH_get_dh(keylength);
+}
+
void
ssl_add_entropy(struct vsf_session* p_sess)
{
diff --git a/tunables.c b/tunables.c
index c737465..1ea7227 100644
--- a/tunables.c
+++ b/tunables.c
@@ -140,6 +140,7 @@ const char* tunable_user_sub_token;
const char* tunable_email_password_file;
const char* tunable_rsa_cert_file;
const char* tunable_dsa_cert_file;
+const char* tunable_dh_param_file;
const char* tunable_ssl_ciphers;
const char* tunable_rsa_private_key_file;
const char* tunable_dsa_private_key_file;
@@ -288,7 +289,9 @@ tunables_load_defaults()
install_str_setting("/usr/share/ssl/certs/vsftpd.pem",
&tunable_rsa_cert_file);
install_str_setting(0, &tunable_dsa_cert_file);
- install_str_setting("ECDHE-RSA-AES256-GCM-SHA384", &tunable_ssl_ciphers);
+ install_str_setting(0, &tunable_dh_param_file);
+ install_str_setting("AES128-SHA:DES-CBC3-SHA:DHE-RSA-AES256-SHA",
+ &tunable_ssl_ciphers);
install_str_setting(0, &tunable_rsa_private_key_file);
install_str_setting(0, &tunable_dsa_private_key_file);
install_str_setting(0, &tunable_ca_certs_file);
diff --git a/tunables.h b/tunables.h
index 9553038..3995472 100644
--- a/tunables.h
+++ b/tunables.h
@@ -142,6 +142,7 @@ extern const char* tunable_user_sub_token;
extern const char* tunable_email_password_file;
extern const char* tunable_rsa_cert_file;
extern const char* tunable_dsa_cert_file;
+extern const char* tunable_dh_param_file;
extern const char* tunable_ssl_ciphers;
extern const char* tunable_rsa_private_key_file;
extern const char* tunable_dsa_private_key_file;
diff --git a/vsftpd.conf.5 b/vsftpd.conf.5
index fb6324e..ff94eca 100644
--- a/vsftpd.conf.5
+++ b/vsftpd.conf.5
@@ -893,6 +893,12 @@ to be in the same file as the certificate.
Default: (none)
.TP
+.B dh_param_file
+This option specifies the location of the custom parameters used for
+ephemeral Diffie-Hellman key exchange in SSL.
+
+Default: (none - use built in parameters appropriate for certificate key size)
+.TP
.B email_password_file
This option can be used to provide an alternate file for usage by the
.BR secure_email_list_enable
--
2.7.4
