[Openvpn-devel,v2,2/2] Add support for OpenSSL TLS 1.3 when using management-external-key

Message ID 20181031165222.5997-2-arne@rfc2549.org
State Superseded
Headers show
Series
  • [Openvpn-devel,v2,1/2] Make tls_version_max return the actual maximum version
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Commit Message

Arne Schwabe Oct. 31, 2018, 4:52 p.m.
For TLS 1.0 to 1.2 and OpenSSL 1.1.0 calls us and requires a PKCS1
padded response. As TLS 1.3 mandates RSA-PSS padding support and also
requires an TLS 1.3 implementation to support RSA-PSS for older TLS
version, OpenSSL will query us to sign an already RSA-PSS padded
string.

This patch adds an 'unpadded' and 'pkcs1' parameter to the
management-external-key option to signal that the client is
able to support pkcs1 as well as unpadded signature requests.

Since clients that implement the management-external-key interface
are usually rather tightly integrated solutions (OpenVPN Connect in the
past, OpenVPN for Android), it is reasonable to expect that
upgrading the OpenSSL library can be done together with
management interface changes. Therefore we provide no backwards
compatbility for mangement-interface clients not supporting
OpenSSL 1.1.1.

Using the management api client version instead might seem like the
more logical way but since we only now that version very late,
it would extra logic and complexity to deal with this asynchronous
behaviour. Instead just give an error early if OpenSSL 1.1.1 and
management-external-key without nopadding is detected.

The interface is prepared for signalling PCKS1 and RSA-PSS support
instead of signalling unpadded support.

Patch v3: fix overlong lines and few other style patches. Note
      two overlong lines concerning mbedtls are not fixed as they
      are removed/shortend by the mbed tls patch to avoid conflicts

Patch v4: Setting minimum TLS version proved to be not enough and
      instead of implementing a whole compability layer we require
      mangement-clients to implement the new feature when they want
      to use OpenSSL 1.1.1

      Add a padding=ALGORITHM argument to pk-sig to indicate the
      algorithm. Drop adding PKCS1 ourselves.

Signed-off-by: Arne Schwabe <arne@rfc2549.org>
---
 doc/management-notes.txt  | 13 ++++++++++-
 doc/openvpn.8             |  7 ++++--
 src/openvpn/manage.c      | 18 +++++++++++---
 src/openvpn/manage.h      | 26 ++++++++++++++-------
 src/openvpn/options.c     | 45 ++++++++++++++++++++++++++++++++---
 src/openvpn/ssl_mbedtls.c |  7 ++++--
 src/openvpn/ssl_openssl.c | 49 +++++++++++++++++++++++++++++++--------
 7 files changed, 136 insertions(+), 29 deletions(-)

Patch

diff --git a/doc/management-notes.txt b/doc/management-notes.txt
index 17645c1d..f685af28 100644
--- a/doc/management-notes.txt
+++ b/doc/management-notes.txt
@@ -816,6 +816,7 @@  actual private key. When the SSL protocol needs to perform a sign
 operation, the data to be signed will be sent to the management interface
 via a notification as follows:
 
+>PK_SIGN:[BASE64_DATA],[ALG] (if client announces support for management version > 2)
 >PK_SIGN:[BASE64_DATA] (if client announces support for management version > 1)
 >RSA_SIGN:[BASE64_DATA] (only older clients will be prompted like this)
 
@@ -823,7 +824,7 @@  The management interface client should then create an appropriate signature of
 the (decoded) BASE64_DATA using the private key and return the SSL signature as
 follows:
 
-pk-sig   (or rsa-sig)
+pk-sig (or rsa-sig)
 [BASE64_SIG_LINE]
 .
 .
@@ -833,6 +834,12 @@  END
 Base 64 encoded output of RSA_private_encrypt for RSA or ECDSA_sign()
 for EC using OpenSSL or mbedtls_pk_sign() using mbed TLS will provide a
 correct signature.
+The rsa-sig interfaces expects PKCS1 padded signatures for RSA keys
+(RSA_PKCS1_PADDING). EC signatures are always unpadded.
+
+The padding field is only present when pk-sig is used and
+currently the following values can be requested PCKS1 and NOPADDING for RSA
+certificates and NOPADDING for EC certificates.
 
 This capability is intended to allow the use of arbitrary cryptographic
 service providers with OpenVPN via the management interface.
@@ -840,6 +847,10 @@  service providers with OpenVPN via the management interface.
 New and updated clients are expected to use the version command to announce
 a version > 1 and handle '>PK_SIGN' prompt and respond with 'pk-sig'.
 
+The older rsa-sig and pk-sig interfaces hav no capability to indidicate the
+requested padding algorithm. When the 'nopadding' using version >= 2 is required.
+To support TLS 1.3 with OpenSSL 1.1.1 supporting unpadded signatures is required.
+
 COMMAND -- certificate (OpenVPN 2.4 or higher)
 ----------------------------------------------
 Provides support for external storage of the certificate. Requires the
diff --git a/doc/openvpn.8 b/doc/openvpn.8
index e80d4696..3cd5d944 100644
--- a/doc/openvpn.8
+++ b/doc/openvpn.8
@@ -2739,10 +2739,13 @@  Allow management interface to override
 directives (client\-only).
 .\"*********************************************************
 .TP
-.B \-\-management\-external\-key
+.B \-\-management\-external\-key [nopadding] [pkcs1]
 Allows usage for external private key file instead of
 .B \-\-key
-option (client\-only).
+option (client\-only). The optional parameters nopadding and
+pkcs1 signal support for different padding algorithms. See
+doc/mangement-notes.txt for a complete description of this
+feature.
 .\"*********************************************************
 .TP
 .B \-\-management\-external\-cert certificate\-hint
diff --git a/src/openvpn/manage.c b/src/openvpn/manage.c
index 8b633f20..62d4bc7b 100644
--- a/src/openvpn/manage.c
+++ b/src/openvpn/manage.c
@@ -3639,18 +3639,30 @@  management_query_multiline_flatten(struct management *man,
 
 char *
 /* returns allocated base64 signature */
-management_query_pk_sig(struct management *man,
-                         const char *b64_data)
+management_query_pk_sig(struct management *man, const char *b64_data,
+                        const char *padding)
 {
     const char *prompt = "PK_SIGN";
     const char *desc = "pk-sign";
+    struct buffer buf_data = alloc_buf(strlen(b64_data) + strlen(padding) + 20);
+
     if (man->connection.client_version <= 1)
     {
         prompt = "RSA_SIGN";
         desc = "rsa-sign";
     }
-    return management_query_multiline_flatten(man, b64_data, prompt, desc,
+
+    buf_write(&buf_data, b64_data, (int) strlen(b64_data));
+    if (man->connection.client_version > 2)
+    {
+        buf_write(&buf_data, ",", (int) strlen(","));
+        buf_write(&buf_data, padding, (int) strlen(padding));
+    }
+    char* ret = management_query_multiline_flatten(man,
+            (char *)buf_bptr(&buf_data), prompt, desc,
             &man->connection.ext_key_state, &man->connection.ext_key_input);
+    free_buf(&buf_data);
+    return ret;
 }
 
 char *
diff --git a/src/openvpn/manage.h b/src/openvpn/manage.h
index d24abe09..5c35a5ca 100644
--- a/src/openvpn/manage.h
+++ b/src/openvpn/manage.h
@@ -31,7 +31,7 @@ 
 #include "socket.h"
 #include "mroute.h"
 
-#define MANAGEMENT_VERSION                      2
+#define MANAGEMENT_VERSION                      3
 #define MANAGEMENT_N_PASSWORD_RETRIES           3
 #define MANAGEMENT_LOG_HISTORY_INITIAL_SIZE   100
 #define MANAGEMENT_ECHO_BUFFER_SIZE           100
@@ -341,12 +341,18 @@  struct management *management_init(void);
 #ifdef MANAGEMENT_PF
 #define MF_CLIENT_PF         (1<<7)
 #endif
-#define MF_UNIX_SOCK       (1<<8)
-#define MF_EXTERNAL_KEY    (1<<9)
-#define MF_UP_DOWN          (1<<10)
-#define MF_QUERY_REMOTE     (1<<11)
-#define MF_QUERY_PROXY      (1<<12)
-#define MF_EXTERNAL_CERT    (1<<13)
+#define MF_UNIX_SOCK                (1<<8)
+#define MF_EXTERNAL_KEY             (1<<9)
+#define MF_EXTERNAL_KEY_NOPADDING   (1<<10)
+#define MF_EXTERNAL_KEY_PKCS1PAD    (1<<11)
+#define MF_UP_DOWN                  (1<<12)
+#define MF_QUERY_REMOTE             (1<<13)
+#define MF_QUERY_PROXY              (1<<14)
+#define MF_EXTERNAL_CERT            (1<<15)
+
+#define MF_RSA_PKCS1_PADDING       1
+#define MF_RSA_NO_PADDING          2
+
 
 bool management_open(struct management *man,
                      const char *addr,
@@ -430,7 +436,11 @@  void management_learn_addr(struct management *management,
 
 #endif
 
-char *management_query_pk_sig(struct management *man, const char *b64_data);
+#define PKSIG_PKCS1     1
+#define PK
+
+char *management_query_pk_sig(struct management *man, const char *b64_data,
+                              const char* pading);
 
 char *management_query_cert(struct management *man, const char *cert_name);
 
diff --git a/src/openvpn/options.c b/src/openvpn/options.c
index 406669a3..229d6ce3 100644
--- a/src/openvpn/options.c
+++ b/src/openvpn/options.c
@@ -2141,6 +2141,22 @@  options_postprocess_verify_ce(const struct options *options, const struct connec
 
 #endif
 
+#if defined(ENABLE_CRYPTOAPI)
+    if (o->cryptoapi_cert && (tls_version_max() >= TLS_VER_1_3))
+    {
+        msg(M_ERR, "Cryptoapi support currently is incompatible "
+                   "with OpenSSL 1.1.1/TLS 1.3");
+    }
+#endif
+#if  defined(ENABLE_MANAGEMENT)
+    if ((options->management_flags & MF_EXTERNAL_KEY) &&
+        !(options->management_flags & (MF_EXTERNAL_KEY_NOPADDING))
+        )
+    {
+        msg(M_ERR, "management-external-key with OpenSSL 1.1.1 requires "
+                   "the nopadding argument/support");
+    }
+#endif
     /*
      * Windows-specific options.
      */
@@ -3068,7 +3084,6 @@  options_postprocess_mutate(struct options *o)
         options_postprocess_http_proxy_override(o);
     }
 #endif
-
 #if P2MP
     /*
      * Save certain parms before modifying options via --pull
@@ -5151,9 +5166,33 @@  add_option(struct options *options,
         options->management_write_peer_info_file = p[1];
     }
 #ifdef ENABLE_MANAGEMENT
-    else if (streq(p[0], "management-external-key") && !p[1])
+    else if (streq(p[0], "management-external-key"))
     {
         VERIFY_PERMISSION(OPT_P_GENERAL);
+        for (int j = 1; j < MAX_PARMS && p[j] != NULL; ++j)
+        {
+            if (streq(p[j], "nopadding"))
+            {
+                options->management_flags |= MF_EXTERNAL_KEY_NOPADDING;
+            }
+            else if (p[1] && streq(p[1], "pkcs1"))
+            {
+                options->management_flags |= MF_EXTERNAL_KEY_PKCS1PAD;
+            }
+            else
+            {
+                msg(msglevel, "Unknown management-external-key flag: %s" , p[j]);
+            }
+        }
+        /*
+         * When no option is present, assume that only PKCS1
+         * padding is supported
+         */
+        if (! (options->management_flags &
+            (MF_EXTERNAL_KEY_NOPADDING | MF_EXTERNAL_KEY_PKCS1PAD)))
+        {
+            options->management_flags |= MF_EXTERNAL_KEY_PKCS1PAD;
+        }
         options->management_flags |= MF_EXTERNAL_KEY;
     }
     else if (streq(p[0], "management-external-cert") && p[1] && !p[2])
@@ -8456,4 +8495,4 @@  add_option(struct options *options,
     }
 err:
     gc_free(&gc);
-}
\ No newline at end of file
+}
diff --git a/src/openvpn/ssl_mbedtls.c b/src/openvpn/ssl_mbedtls.c
index f7e8c2d0..09b1a8fa 100644
--- a/src/openvpn/ssl_mbedtls.c
+++ b/src/openvpn/ssl_mbedtls.c
@@ -626,7 +626,6 @@  tls_ctx_use_external_signing_func(struct tls_root_ctx *ctx,
 }
 
 #ifdef ENABLE_MANAGEMENT
-
 /** Query the management interface for a signature, see external_sign_func. */
 static bool
 management_sign_func(void *sign_ctx, const void *src, size_t src_len,
@@ -641,7 +640,11 @@  management_sign_func(void *sign_ctx, const void *src, size_t src_len,
         goto cleanup;
     }
 
-    if (!(dst_b64 = management_query_pk_sig(management, src_b64)))
+    /*
+     * We only use PKCS1 signatures at the moment in mbed TLS,
+     * there the signature parameter is hardcoded
+     */
+    if (!(dst_b64 = management_query_pk_sig(management, src_b64, "PKCS1")))
     {
         goto cleanup;
     }
diff --git a/src/openvpn/ssl_openssl.c b/src/openvpn/ssl_openssl.c
index c2c8fdc0..237c2b55 100644
--- a/src/openvpn/ssl_openssl.c
+++ b/src/openvpn/ssl_openssl.c
@@ -1079,24 +1079,46 @@  openvpn_extkey_rsa_finish(RSA *rsa)
     return 1;
 }
 
-/* Pass the input hash in 'dgst' to management and get the signature back.
+/*
+ * Convert OpenSSL's constant to the strings used in the management
+ * interface query
+ */
+const char*
+get_sig_padding_name(const int padding)
+{
+    switch(padding)
+    {
+        case RSA_PKCS1_PADDING:
+            return "PKCS1";
+        case RSA_NO_PADDING:
+            return "NOPADDING";
+        default:
+            return "UNKNOWN";
+    }
+}
+
+/*
+ * Pass the input hash in 'dgst' to management and get the signature back.
  * On input siglen contains the capacity of the buffer 'sig'.
  * On return signature is in sig.
+ * pkcs1 controls if pkcs1 padding is required
  * Return value is signature length or -1 on error.
  */
 static int
 get_sig_from_man(const unsigned char *dgst, unsigned int dgstlen,
-                 unsigned char *sig, unsigned int siglen)
+                 unsigned char *sig, unsigned int siglen,
+                 int padding)
 {
     char *in_b64 = NULL;
     char *out_b64 = NULL;
     int len = -1;
 
-    /* convert 'dgst' to base64 */
-    if (management
-        && openvpn_base64_encode(dgst, dgstlen, &in_b64) > 0)
+    int bencret = openvpn_base64_encode(dgst, dgstlen, &in_b64);
+
+    if (management && bencret > 0)
     {
-        out_b64 = management_query_pk_sig(management, in_b64);
+        out_b64 = management_query_pk_sig(management, in_b64,
+                                          get_sig_padding_name(padding));
     }
     if (out_b64)
     {
@@ -1110,18 +1132,19 @@  get_sig_from_man(const unsigned char *dgst, unsigned int dgstlen,
 
 /* sign arbitrary data */
 static int
-rsa_priv_enc(int flen, const unsigned char *from, unsigned char *to, RSA *rsa, int padding)
+rsa_priv_enc(int flen, const unsigned char *from, unsigned char *to, RSA *rsa,
+             int padding)
 {
     unsigned int len = RSA_size(rsa);
     int ret = -1;
 
-    if (padding != RSA_PKCS1_PADDING)
+    if (padding != RSA_PKCS1_PADDING && padding != RSA_NO_PADDING)
     {
         RSAerr(RSA_F_RSA_OSSL_PRIVATE_ENCRYPT, RSA_R_UNKNOWN_PADDING_TYPE);
         return -1;
     }
 
-    ret = get_sig_from_man(from, flen, to, len);
+    ret = get_sig_from_man(from, flen, to, len, padding);
 
     return (ret == len)? ret : -1;
 }
@@ -1215,7 +1238,13 @@  ecdsa_sign(int type, const unsigned char *dgst, int dgstlen, unsigned char *sig,
            unsigned int *siglen, const BIGNUM *kinv, const BIGNUM *r, EC_KEY *ec)
 {
     int capacity = ECDSA_size(ec);
-    int len = get_sig_from_man(dgst, dgstlen, sig, capacity);
+    /*
+     * ECDSA does not seem to have proper constants for paddings since
+     * there are only signatures without padding at the moment, reuse
+     * RSA_NO_PADDING for now as it will trigger querying for "NOPADDING" in the
+     * management interface
+     */
+    int len = get_sig_from_man(dgst, dgstlen, sig, capacity, RSA_NO_PADDING);
 
     if (len > 0)
     {