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 21/59] 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

-- 

2.14.4