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[Openvpn-devel] [PATCH 1/2] Normalise ncp-ciphers option and restrict it to 127 bytes
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From: Arne S. <ar...@rf...> - 2020-08-30 14:30:22
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In scenarios of mbed TLS vs OpenSSL we already normalise the ciphers
that are send via the wire protocol via OCC to not have a mismatch
warning between server and client. This is done by
translate_cipher_name_from_openvpn. The same applies also to the
ncp-ciphers list. Specifying non normalised names in ncp-ciphers will
cause negotation not to succeed if ciphers are not in the same form.
Therefore we will normalise the ciphers in options_postmutate.
The alternative and a lot less user friendly alternative would be to
bail if on of the ciphers in ncp-ciphers is not in its normalised form.
Also restrict the ncp-ciphers list to 127. This is somewhat arbitrary
but should prevent too large IV_CIPHER messages and problems sending
those. The server will accept also large IV_CIPHER values from clients.
Cherry picked from be4531564e2be7c8a0222e6923e3f7580b358cab and adjusted
for 2.4 (methods added to ssl.h/ssl.c instead ssl_ncp.c/.h
Signed-off-by: Arne Schwabe <ar...@rf...>
---
doc/openvpn.8 | 2 +
src/openvpn/options.c | 9 ++++
src/openvpn/ssl.c | 63 +++++++++++++++++++++++
src/openvpn/ssl.h | 23 +++++++++
src/openvpn/ssl_ncp.h | 116 ++++++++++++++++++++++++++++++++++++++++++
5 files changed, 213 insertions(+)
create mode 100644 src/openvpn/ssl_ncp.h
diff --git a/doc/openvpn.8 b/doc/openvpn.8
index 8038e1f4..77cc361d 100644
--- a/doc/openvpn.8
+++ b/doc/openvpn.8
@@ -4273,6 +4273,8 @@ NCP server (v2.4+) with "\-\-cipher BF\-CBC" and "\-\-ncp\-ciphers
AES\-256\-GCM:AES\-256\-CBC" set can either specify "\-\-cipher BF\-CBC" or
"\-\-cipher AES\-256\-CBC" and both will work.
+This list is restricted to be 127 chars long after conversion to OpenVPN
+ciphers.
.\"*********************************************************
.TP
.B \-\-ncp\-disable
diff --git a/src/openvpn/options.c b/src/openvpn/options.c
index de30fcb0..f69bbb22 100644
--- a/src/openvpn/options.c
+++ b/src/openvpn/options.c
@@ -2982,6 +2982,15 @@ options_postprocess_mutate(struct options *o)
options_postprocess_mutate_invariant(o);
+ if (o->ncp_enabled)
+ {
+ o->ncp_ciphers = mutate_ncp_cipher_list(o->ncp_ciphers, &o->gc);
+ if (o->ncp_ciphers == NULL)
+ {
+ msg(M_USAGE, "NCP cipher list contains unsupported ciphers or is too long.");
+ }
+ }
+
if (o->remote_list && !o->connection_list)
{
/*
diff --git a/src/openvpn/ssl.c b/src/openvpn/ssl.c
index 215147f3..dd9c52fb 100644
--- a/src/openvpn/ssl.c
+++ b/src/openvpn/ssl.c
@@ -4318,6 +4318,69 @@ delayed_auth_pass_purge(void)
purge_user_pass(&auth_user_pass, false);
}
+char *
+mutate_ncp_cipher_list(const char *list, struct gc_arena *gc)
+{
+ bool error_found = false;
+
+ struct buffer new_list = alloc_buf(MAX_NCP_CIPHERS_LENGTH);
+
+ char *const tmp_ciphers = string_alloc(list, NULL);
+ const char *token = strtok(tmp_ciphers, ":");
+ while (token)
+ {
+ /*
+ * Going through a roundtrip by using translate_cipher_name_from_openvpn
+ * and translate_cipher_name_to_openvpn also normalises the cipher name,
+ * e.g. replacing AeS-128-gCm with AES-128-GCM
+ */
+ const char *cipher_name = translate_cipher_name_from_openvpn(token);
+ const cipher_kt_t *ktc = cipher_kt_get(cipher_name);
+ if (!ktc)
+ {
+ msg(M_WARN, "Unsupported cipher in --ncp-ciphers: %s", token);
+ error_found = true;
+ }
+ else
+ {
+ const char *ovpn_cipher_name =
+ translate_cipher_name_to_openvpn(cipher_kt_name(ktc));
+
+ if (buf_len(&new_list)> 0)
+ {
+ /* The next if condition ensure there is always space for
+ * a :
+ */
+ buf_puts(&new_list, ":");
+ }
+
+ /* Ensure buffer has capacity for cipher name + : + \0 */
+ if (!(buf_forward_capacity(&new_list) >
+ strlen(ovpn_cipher_name) + 2))
+ {
+ msg(M_WARN, "Length of --ncp-ciphers is over the "
+ "limit of 127 chars");
+ error_found = true;
+ }
+ else
+ {
+ buf_puts(&new_list, ovpn_cipher_name);
+ }
+ }
+ token = strtok(NULL, ":");
+ }
+
+ char *ret = NULL;
+ if (!error_found && buf_len(&new_list) > 0)
+ {
+ buf_null_terminate(&new_list);
+ ret = string_alloc(buf_str(&new_list), gc);
+ }
+ free(tmp_ciphers);
+ free_buf(&new_list);
+
+ return ret;
+}
#else /* if defined(ENABLE_CRYPTO) */
static void
dummy(void)
diff --git a/src/openvpn/ssl.h b/src/openvpn/ssl.h
index 3266f386..703de99b 100644
--- a/src/openvpn/ssl.h
+++ b/src/openvpn/ssl.h
@@ -527,6 +527,29 @@ bool tls_check_ncp_cipher_list(const char *list);
*/
bool tls_item_in_cipher_list(const char *item, const char *list);
+/**
+ * Check whether the ciphers in the supplied list are supported.
+ *
+ * @param list Colon-separated list of ciphers
+ * @parms gc gc_arena to allocate the returned string
+ *
+ * @returns colon separated string of normalised (via
+ * translate_cipher_name_from_openvpn) and
+ * zero terminated string iff all ciphers
+ * in list are supported and the total length
+ * is short than MAX_NCP_CIPHERS_LENGTH. NULL
+ * otherwise.
+ */
+char *
+mutate_ncp_cipher_list(const char *list, struct gc_arena *gc);
+
+/**
+ * The maximum length of a ncp-cipher string that is accepted.
+ *
+ * Since this list needs to be pushed as IV_CIPHERS, we are conservative
+ * about its length.
+ */
+#define MAX_NCP_CIPHERS_LENGTH 127
/*
* inline functions
diff --git a/src/openvpn/ssl_ncp.h b/src/openvpn/ssl_ncp.h
new file mode 100644
index 00000000..d00c222d
--- /dev/null
+++ b/src/openvpn/ssl_ncp.h
@@ -0,0 +1,116 @@
+/*
+ * OpenVPN -- An application to securely tunnel IP networks
+ * over a single TCP/UDP port, with support for SSL/TLS-based
+ * session authentication and key exchange,
+ * packet encryption, packet authentication, and
+ * packet compression.
+ *
+ * Copyright (C) 2002-2018 OpenVPN Inc <sa...@op...>
+ * Copyright (C) 2010-2018 Fox Crypto B.V. <op...@fo...>
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 2
+ * as published by the Free Software Foundation.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License along
+ * with this program; if not, write to the Free Software Foundation, Inc.,
+ * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
+ */
+
+/**
+ * @file Control Channel SSL/Data dynamic negotion Module
+ * This file is split from ssl.h to be able to unit test it.
+ */
+
+#ifndef OPENVPN_SSL_NCP_H
+#define OPENVPN_SSL_NCP_H
+
+#include "buffer.h"
+#include "options.h"
+
+/**
+ * Returns whether the client supports NCP either by
+ * announcing IV_NCP>=2 or the IV_CIPHERS list
+ */
+bool
+tls_peer_supports_ncp(const char *peer_info);
+
+/**
+ * "Poor man's NCP": Use peer cipher if it is an allowed (NCP) cipher.
+ * Allows non-NCP peers to upgrade their cipher individually.
+ *
+ * Make sure to call tls_session_update_crypto_params() after calling this
+ * function.
+ */
+void tls_poor_mans_ncp(struct options *o, const char *remote_ciphername);
+
+/**
+ * Iterates through the ciphers in server_list and return the first
+ * cipher that is also supported by the peer according to the IV_NCP
+ * and IV_CIPHER values in peer_info.
+ *
+ * We also accept a cipher that is the remote cipher of the client for
+ * "Poor man's NCP": Use peer cipher if it is an allowed (NCP) cipher.
+ * Allows non-NCP peers to upgrade their cipher individually.
+ *
+ * Make sure to call tls_session_update_crypto_params() after calling this
+ * function.
+ *
+ * @param gc gc arena that is ONLY used to allocate the returned string
+ *
+ * @returns NULL if no common cipher is available, otherwise the best common
+ * cipher
+ */
+char *
+ncp_get_best_cipher(const char *server_list, const char *server_cipher,
+ const char *peer_info, const char *remote_cipher,
+ struct gc_arena *gc);
+
+
+/**
+ * Returns the support cipher list from the peer according to the IV_NCP
+ * and IV_CIPHER values in peer_info.
+ *
+ * @returns Either a string containing the ncp list that is either static
+ * or allocated via gc. If no information is available an empty string
+ * ("") is returned.
+ */
+const char *
+tls_peer_ncp_list(const char *peer_info, struct gc_arena *gc);
+
+/**
+ * Check whether the ciphers in the supplied list are supported.
+ *
+ * @param list Colon-separated list of ciphers
+ * @parms gc gc_arena to allocate the returned string
+ *
+ * @returns colon separated string of normalised (via
+ * translate_cipher_name_from_openvpn) and
+ * zero terminated string iff all ciphers
+ * in list are supported and the total length
+ * is short than MAX_NCP_CIPHERS_LENGTH. NULL
+ * otherwise.
+ */
+char *
+mutate_ncp_cipher_list(const char *list, struct gc_arena *gc);
+
+/**
+ * Return true iff item is present in the colon-separated zero-terminated
+ * cipher list.
+ */
+bool tls_item_in_cipher_list(const char *item, const char *list);
+
+/**
+ * The maximum length of a ncp-cipher string that is accepted.
+ *
+ * Since this list needs to be pushed as IV_CIPHERS, we are conservative
+ * about its length.
+ */
+#define MAX_NCP_CIPHERS_LENGTH 127
+
+#endif /* ifndef OPENVPN_SSL_NCP_H */
--
2.26.2
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