Message ID | 20200812085539.19620-1-arne@rfc2549.org |
---|---|
State | Superseded |
Headers | show |
Series | [Openvpn-devel,1/3] Refactor key_state_export_keying_material functions | expand |
Hi, Couldn't resist giving this a quick look. Feature-ACK on the patch set, but some comments on the approach: On 12-08-2020 10:55, Arne Schwabe wrote: > This refactors the common code between mbed SSL and OpenSSL into > export_user_keying_material and also prepares the backend functions > to export more than one key. > > Also fix checking the return value of SSL_export_keying_material > only 1 is a sucess, -1 is also an error. > > Signed-off-by: Arne Schwabe <arne@rfc2549.org> > --- > src/openvpn/ssl.c | 33 ++++++++++++++++++++++++- > src/openvpn/ssl_backend.h | 18 ++++++++++++-- > src/openvpn/ssl_mbedtls.c | 22 ++++++----------- > src/openvpn/ssl_openssl.c | 51 +++++++++++++++++++++------------------ > 4 files changed, 83 insertions(+), 41 deletions(-) > > diff --git a/src/openvpn/ssl.c b/src/openvpn/ssl.c > index f16114c2..390114e1 100644 > --- a/src/openvpn/ssl.c > +++ b/src/openvpn/ssl.c > @@ -2412,6 +2412,37 @@ error: > return false; > } > > +static void > +export_user_keying_material(struct key_state_ssl *ssl, > + struct tls_session *session) > +{ > + if (session->opt->ekm_size > 0) > + { > + unsigned int size = session->opt->ekm_size; > + struct gc_arena gc = gc_new(); > + > + unsigned char *ekm; > + if ((ekm = key_state_export_keying_material(ssl, session, > + EXPORT_KEY_USER, &gc))) > + { Hmm, I don't think these abstractions are right. I would argue that the crypto backends should know as few about OpenVPN specifics as possible. So things like "EXPORT_KEY_USER" should probably not be passed to the backend, and instead be handled in ssl.c. Why not give the backend a prototype like key_state_export_keying_material(label, label_len, ekm, ekm_len) I understand that this would mean an extra memcpy() for the mbedtls code, but this is not performance-critical at all, right? (In the follow-up patch, just cache the master secret and client/server random, instead of the derived key material in the mbedtls backend, so you can generate the export at will. For OpenSSL, this API should be trivial.) > + unsigned int len = (size * 2) + 2; > + > + const char *key = format_hex_ex(ekm, size, len, 0, NULL, &gc); > + setenv_str(session->opt->es, "exported_keying_material", key); > + > + dmsg(D_TLS_DEBUG_MED, "%s: exported keying material: %s", > + __func__, key); > + secure_memzero(ekm, size); > + } > + else > + { > + msg(M_WARN, "WARNING: Export keying material failed!"); > + setenv_del(session->opt->es, "exported_keying_material"); > + } > + gc_free(&gc); > + } > +} > + > /** > * Handle reading key data, peer-info, username/password, OCC > * from the TLS control channel (cleartext). > @@ -2541,7 +2572,7 @@ key_method_2_read(struct buffer *buf, struct tls_multi *multi, struct tls_sessio > if ((ks->authenticated > KS_AUTH_FALSE) > && plugin_defined(session->opt->plugins, OPENVPN_PLUGIN_TLS_FINAL)) > { > - key_state_export_keying_material(&ks->ks_ssl, session); > + export_user_keying_material(&ks->ks_ssl, session); > > if (plugin_call(session->opt->plugins, OPENVPN_PLUGIN_TLS_FINAL, NULL, NULL, session->opt->es) != OPENVPN_PLUGIN_FUNC_SUCCESS) > { > diff --git a/src/openvpn/ssl_backend.h b/src/openvpn/ssl_backend.h > index 7f52ab1e..8faaefd5 100644 > --- a/src/openvpn/ssl_backend.h > +++ b/src/openvpn/ssl_backend.h > @@ -389,18 +389,32 @@ void key_state_ssl_free(struct key_state_ssl *ks_ssl); > void backend_tls_ctx_reload_crl(struct tls_root_ctx *ssl_ctx, > const char *crl_file, bool crl_inline); > > + > +/* defines the different RFC5705 that are used in OpenVPN */ Make this /** to have it turn up nicely in the doxygen. > +enum export_key_identifier { > + EXPORT_KEY_USER > +}; > + > /** > * Keying Material Exporters [RFC 5705] allows additional keying material to be > * derived from existing TLS channel. This exported keying material can then be > * used for a variety of purposes. > * > + * Note > + * Note ... what? > * @param ks_ssl The SSL channel's state info > * @param session The session associated with the given key_state > + * @param key The key to export. > + * @param gc gc_arena that might be used to allocate a string Where "a string" is "the keying material", right? Maybe just say that :) > + * @returns The exported key material, the caller may zero the > + * string but should not free it > */ > > -void > +unsigned char* > key_state_export_keying_material(struct key_state_ssl *ks_ssl, > - struct tls_session *session) __attribute__((nonnull)); > + struct tls_session *session, > + enum export_key_identifier export_key, > + struct gc_arena *gc) __attribute__((nonnull)); > > /**************************************************************************/ > /** @addtogroup control_tls > diff --git a/src/openvpn/ssl_mbedtls.c b/src/openvpn/ssl_mbedtls.c > index 9c874788..8ae6ec7b 100644 > --- a/src/openvpn/ssl_mbedtls.c > +++ b/src/openvpn/ssl_mbedtls.c > @@ -231,24 +231,18 @@ mbedtls_ssl_export_keys_cb(void *p_expkey, const unsigned char *ms, > } > #endif /* HAVE_EXPORT_KEYING_MATERIAL */ > > -void > +unsigned char * > key_state_export_keying_material(struct key_state_ssl *ssl, > - struct tls_session *session) > + struct tls_session *session, > + enum export_key_identifier key_id, > + struct gc_arena *gc) > { > - if (ssl->exported_key_material) > + if (key_id == EXPORT_KEY_USER) > { > - unsigned int size = session->opt->ekm_size; > - struct gc_arena gc = gc_new(); > - unsigned int len = (size * 2) + 2; > - > - const char *key = format_hex_ex(ssl->exported_key_material, > - size, len, 0, NULL, &gc); > - setenv_str(session->opt->es, "exported_keying_material", key); > - > - dmsg(D_TLS_DEBUG_MED, "%s: exported keying material: %s", > - __func__, key); > - gc_free(&gc); > + return ssl->exported_key_material; > } > + > + return NULL; > } > > > diff --git a/src/openvpn/ssl_openssl.c b/src/openvpn/ssl_openssl.c > index 5ba74402..1aad4f89 100644 > --- a/src/openvpn/ssl_openssl.c > +++ b/src/openvpn/ssl_openssl.c > @@ -158,35 +158,38 @@ tls_ctx_initialised(struct tls_root_ctx *ctx) > return NULL != ctx->ctx; > } > > -void > +unsigned char * > key_state_export_keying_material(struct key_state_ssl *ssl, > - struct tls_session *session) > + struct tls_session *session, > + enum export_key_identifier key_id, > + struct gc_arena *gc) > + > { > - if (session->opt->ekm_size > 0) > - { > - unsigned int size = session->opt->ekm_size; > - struct gc_arena gc = gc_new(); > - unsigned char *ekm = (unsigned char *) gc_malloc(size, true, &gc); > + const char *label; > + size_t label_size, ekm_size; > > - if (SSL_export_keying_material(ssl->ssl, ekm, size, > - session->opt->ekm_label, > - session->opt->ekm_label_size, > - NULL, 0, 0)) > - { > - unsigned int len = (size * 2) + 2; > + if (key_id == EXPORT_KEY_USER) > + { > + label = session->opt->ekm_label; > + label_size = session->opt->ekm_label_size; > + ekm_size = session->opt->ekm_size; > + } > + else > + { > + ASSERT(0); > + } > > - const char *key = format_hex_ex(ekm, size, len, 0, NULL, &gc); > - setenv_str(session->opt->es, "exported_keying_material", key); > + unsigned char *ekm = (unsigned char *) gc_malloc(ekm_size, true, gc); > > - dmsg(D_TLS_DEBUG_MED, "%s: exported keying material: %s", > - __func__, key); > - } > - else > - { > - msg(M_WARN, "WARNING: Export keying material failed!"); > - setenv_del(session->opt->es, "exported_keying_material"); > - } > - gc_free(&gc); > + if (SSL_export_keying_material(ssl->ssl, ekm, ekm_size, label, > + label_size, NULL, 0, 0) == 1) > + { > + return ekm; > + } > + else > + { > + secure_memzero(ekm, ekm_size); > + return NULL; > } > } > > -Steffan.
diff --git a/src/openvpn/ssl.c b/src/openvpn/ssl.c index f16114c2..390114e1 100644 --- a/src/openvpn/ssl.c +++ b/src/openvpn/ssl.c @@ -2412,6 +2412,37 @@ error: return false; } +static void +export_user_keying_material(struct key_state_ssl *ssl, + struct tls_session *session) +{ + if (session->opt->ekm_size > 0) + { + unsigned int size = session->opt->ekm_size; + struct gc_arena gc = gc_new(); + + unsigned char *ekm; + if ((ekm = key_state_export_keying_material(ssl, session, + EXPORT_KEY_USER, &gc))) + { + unsigned int len = (size * 2) + 2; + + const char *key = format_hex_ex(ekm, size, len, 0, NULL, &gc); + setenv_str(session->opt->es, "exported_keying_material", key); + + dmsg(D_TLS_DEBUG_MED, "%s: exported keying material: %s", + __func__, key); + secure_memzero(ekm, size); + } + else + { + msg(M_WARN, "WARNING: Export keying material failed!"); + setenv_del(session->opt->es, "exported_keying_material"); + } + gc_free(&gc); + } +} + /** * Handle reading key data, peer-info, username/password, OCC * from the TLS control channel (cleartext). @@ -2541,7 +2572,7 @@ key_method_2_read(struct buffer *buf, struct tls_multi *multi, struct tls_sessio if ((ks->authenticated > KS_AUTH_FALSE) && plugin_defined(session->opt->plugins, OPENVPN_PLUGIN_TLS_FINAL)) { - key_state_export_keying_material(&ks->ks_ssl, session); + export_user_keying_material(&ks->ks_ssl, session); if (plugin_call(session->opt->plugins, OPENVPN_PLUGIN_TLS_FINAL, NULL, NULL, session->opt->es) != OPENVPN_PLUGIN_FUNC_SUCCESS) { diff --git a/src/openvpn/ssl_backend.h b/src/openvpn/ssl_backend.h index 7f52ab1e..8faaefd5 100644 --- a/src/openvpn/ssl_backend.h +++ b/src/openvpn/ssl_backend.h @@ -389,18 +389,32 @@ void key_state_ssl_free(struct key_state_ssl *ks_ssl); void backend_tls_ctx_reload_crl(struct tls_root_ctx *ssl_ctx, const char *crl_file, bool crl_inline); + +/* defines the different RFC5705 that are used in OpenVPN */ +enum export_key_identifier { + EXPORT_KEY_USER +}; + /** * Keying Material Exporters [RFC 5705] allows additional keying material to be * derived from existing TLS channel. This exported keying material can then be * used for a variety of purposes. * + * Note + * * @param ks_ssl The SSL channel's state info * @param session The session associated with the given key_state + * @param key The key to export. + * @param gc gc_arena that might be used to allocate a string + * @returns The exported key material, the caller may zero the + * string but should not free it */ -void +unsigned char* key_state_export_keying_material(struct key_state_ssl *ks_ssl, - struct tls_session *session) __attribute__((nonnull)); + struct tls_session *session, + enum export_key_identifier export_key, + struct gc_arena *gc) __attribute__((nonnull)); /**************************************************************************/ /** @addtogroup control_tls diff --git a/src/openvpn/ssl_mbedtls.c b/src/openvpn/ssl_mbedtls.c index 9c874788..8ae6ec7b 100644 --- a/src/openvpn/ssl_mbedtls.c +++ b/src/openvpn/ssl_mbedtls.c @@ -231,24 +231,18 @@ mbedtls_ssl_export_keys_cb(void *p_expkey, const unsigned char *ms, } #endif /* HAVE_EXPORT_KEYING_MATERIAL */ -void +unsigned char * key_state_export_keying_material(struct key_state_ssl *ssl, - struct tls_session *session) + struct tls_session *session, + enum export_key_identifier key_id, + struct gc_arena *gc) { - if (ssl->exported_key_material) + if (key_id == EXPORT_KEY_USER) { - unsigned int size = session->opt->ekm_size; - struct gc_arena gc = gc_new(); - unsigned int len = (size * 2) + 2; - - const char *key = format_hex_ex(ssl->exported_key_material, - size, len, 0, NULL, &gc); - setenv_str(session->opt->es, "exported_keying_material", key); - - dmsg(D_TLS_DEBUG_MED, "%s: exported keying material: %s", - __func__, key); - gc_free(&gc); + return ssl->exported_key_material; } + + return NULL; } diff --git a/src/openvpn/ssl_openssl.c b/src/openvpn/ssl_openssl.c index 5ba74402..1aad4f89 100644 --- a/src/openvpn/ssl_openssl.c +++ b/src/openvpn/ssl_openssl.c @@ -158,35 +158,38 @@ tls_ctx_initialised(struct tls_root_ctx *ctx) return NULL != ctx->ctx; } -void +unsigned char * key_state_export_keying_material(struct key_state_ssl *ssl, - struct tls_session *session) + struct tls_session *session, + enum export_key_identifier key_id, + struct gc_arena *gc) + { - if (session->opt->ekm_size > 0) - { - unsigned int size = session->opt->ekm_size; - struct gc_arena gc = gc_new(); - unsigned char *ekm = (unsigned char *) gc_malloc(size, true, &gc); + const char *label; + size_t label_size, ekm_size; - if (SSL_export_keying_material(ssl->ssl, ekm, size, - session->opt->ekm_label, - session->opt->ekm_label_size, - NULL, 0, 0)) - { - unsigned int len = (size * 2) + 2; + if (key_id == EXPORT_KEY_USER) + { + label = session->opt->ekm_label; + label_size = session->opt->ekm_label_size; + ekm_size = session->opt->ekm_size; + } + else + { + ASSERT(0); + } - const char *key = format_hex_ex(ekm, size, len, 0, NULL, &gc); - setenv_str(session->opt->es, "exported_keying_material", key); + unsigned char *ekm = (unsigned char *) gc_malloc(ekm_size, true, gc); - dmsg(D_TLS_DEBUG_MED, "%s: exported keying material: %s", - __func__, key); - } - else - { - msg(M_WARN, "WARNING: Export keying material failed!"); - setenv_del(session->opt->es, "exported_keying_material"); - } - gc_free(&gc); + if (SSL_export_keying_material(ssl->ssl, ekm, ekm_size, label, + label_size, NULL, 0, 0) == 1) + { + return ekm; + } + else + { + secure_memzero(ekm, ekm_size); + return NULL; } }
This refactors the common code between mbed SSL and OpenSSL into export_user_keying_material and also prepares the backend functions to export more than one key. Also fix checking the return value of SSL_export_keying_material only 1 is a sucess, -1 is also an error. Signed-off-by: Arne Schwabe <arne@rfc2549.org> --- src/openvpn/ssl.c | 33 ++++++++++++++++++++++++- src/openvpn/ssl_backend.h | 18 ++++++++++++-- src/openvpn/ssl_mbedtls.c | 22 ++++++----------- src/openvpn/ssl_openssl.c | 51 +++++++++++++++++++++------------------ 4 files changed, 83 insertions(+), 41 deletions(-)