1 files changed, 342 insertions, 0 deletions

diff --git a/src/openvpn/ssl_ncp.c b/src/openvpn/ssl_ncp.c
new file mode 100644
index 0000000..aabfc6d
--- /dev/null
+++ b/src/openvpn/ssl_ncp.c
@@ -0,0 +1,342 @@
+/*
+ *  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) 2002-2021 OpenVPN Inc <sales@openvpn.net>
+ *  Copyright (C) 2010-2021 Fox Crypto B.V. <openvpn@foxcrypto.com>
+ *  Copyright (C) 2008-2021 David Sommerseth <dazo@eurephia.org>
+ *
+ *  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.c to be able to unit test it.
+ */
+
+/*
+ * The routines in this file deal with dynamically negotiating
+ * the data channel HMAC and cipher keys through a TLS session.
+ *
+ * Both the TLS session and the data channel are multiplexed
+ * over the same TCP/UDP port.
+ */
+#ifdef HAVE_CONFIG_H
+#include "config.h"
+#elif defined(_MSC_VER)
+#include "config-msvc.h"
+#endif
+
+#include "syshead.h"
+#include "win32.h"
+
+#include "error.h"
+#include "common.h"
+
+#include "ssl_ncp.h"
+#include "openvpn.h"
+
+/**
+ * Return the Negotiable Crypto Parameters version advertised in the peer info
+ * string, or 0 if none specified.
+ */
+static int
+tls_peer_info_ncp_ver(const char *peer_info)
+{
+    const char *ncpstr = peer_info ? strstr(peer_info, "IV_NCP=") : NULL;
+    if (ncpstr)
+    {
+        int ncp = 0;
+        int r = sscanf(ncpstr, "IV_NCP=%d", &ncp);
+        if (r == 1)
+        {
+            return ncp;
+        }
+    }
+    return 0;
+}
+
+/**
+ * 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)
+{
+    if (!peer_info)
+    {
+        return false;
+    }
+    else if (tls_peer_info_ncp_ver(peer_info) >= 2
+             || strstr(peer_info, "IV_CIPHERS="))
+    {
+        return true;
+    }
+    else
+    {
+        return 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 cipher_kt_get/cipher_kt_name
+         * (and translate_cipher_name_from_openvpn/
+         * translate_cipher_name_to_openvpn) also normalises the cipher name,
+         * e.g. replacing AeS-128-gCm with AES-128-GCM
+         */
+        const cipher_kt_t *ktc = cipher_kt_get(token);
+        if (strcmp(token, "none") == 0)
+        {
+            msg(M_WARN, "WARNING: cipher 'none' specified for --data-ciphers. "
+                        "This allows negotiation of NO encryption and "
+                        "tunnelled data WILL then be transmitted in clear text "
+                        "over the network! "
+                        "PLEASE DO RECONSIDER THIS SETTING!");
+        }
+        if (!ktc && strcmp(token, "none") != 0)
+        {
+            msg(M_WARN, "Unsupported cipher in --data-ciphers: %s", token);
+            error_found = true;
+        }
+        else
+        {
+            const char *ovpn_cipher_name = cipher_kt_name(ktc);
+            if (ktc == NULL)
+            {
+                /* NULL resolves to [null-cipher] but we need none for
+                 * data-ciphers */
+                ovpn_cipher_name = "none";
+            }
+
+            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 --data-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;
+}
+
+bool
+tls_item_in_cipher_list(const char *item, const char *list)
+{
+    char *tmp_ciphers = string_alloc(list, NULL);
+    char *tmp_ciphers_orig = tmp_ciphers;
+
+    const char *token = strtok(tmp_ciphers, ":");
+    while (token)
+    {
+        if (0 == strcmp(token, item))
+        {
+            break;
+        }
+        token = strtok(NULL, ":");
+    }
+    free(tmp_ciphers_orig);
+
+    return token != NULL;
+}
+
+const char *
+tls_peer_ncp_list(const char *peer_info, struct gc_arena *gc)
+{
+    /* Check if the peer sends the IV_CIPHERS list */
+    const char *ncp_ciphers_start;
+    if (peer_info && (ncp_ciphers_start = strstr(peer_info, "IV_CIPHERS=")))
+    {
+        ncp_ciphers_start += strlen("IV_CIPHERS=");
+        const char *ncp_ciphers_end = strstr(ncp_ciphers_start, "\n");
+        if (!ncp_ciphers_end)
+        {
+            /* IV_CIPHERS is at end of the peer_info list and no '\n'
+             * follows */
+            ncp_ciphers_end = ncp_ciphers_start + strlen(ncp_ciphers_start);
+        }
+
+        char *ncp_ciphers_peer = string_alloc(ncp_ciphers_start, gc);
+        /* NULL terminate the copy at the right position */
+        ncp_ciphers_peer[ncp_ciphers_end - ncp_ciphers_start] = '\0';
+        return ncp_ciphers_peer;
+
+    }
+    else if (tls_peer_info_ncp_ver(peer_info)>=2)
+    {
+        /* If the peer announces IV_NCP=2 then it supports the AES GCM
+         * ciphers */
+        return "AES-256-GCM:AES-128-GCM";
+    }
+    else
+    {
+        return "";
+    }
+}
+
+char *
+ncp_get_best_cipher(const char *server_list, const char *peer_info,
+                    const char *remote_cipher, struct gc_arena *gc)
+{
+    /*
+     * The gc of the parameter is tied to the VPN session, create a
+     * short lived gc arena that is only valid for the duration of
+     * this function
+     */
+
+    struct gc_arena gc_tmp = gc_new();
+
+    const char *peer_ncp_list = tls_peer_ncp_list(peer_info, &gc_tmp);
+
+    /* non-NCP client without OCC?  "assume nothing" */
+    /* For client doing the newer version of NCP (that send IV_CIPHER)
+     * we cannot assume that they will accept remote_cipher */
+    if (remote_cipher == NULL ||
+        (peer_info && strstr(peer_info, "IV_CIPHERS=")))
+    {
+        remote_cipher = "";
+    }
+
+    char *tmp_ciphers = string_alloc(server_list, &gc_tmp);
+
+    const char *token;
+    while ((token = strsep(&tmp_ciphers, ":")))
+    {
+        if (tls_item_in_cipher_list(token, peer_ncp_list)
+            || streq(token, remote_cipher))
+        {
+            break;
+        }
+    }
+
+    char *ret = NULL;
+    if (token != NULL)
+    {
+        ret = string_alloc(token, gc);
+    }
+
+    gc_free(&gc_tmp);
+    return ret;
+}
+
+/**
+ * "Poor man's NCP": Use peer cipher if it is an allowed (NCP) cipher.
+ * Allows non-NCP peers to upgrade their cipher individually.
+ *
+ * Returns true if we switched to the peer's cipher
+ *
+ * Make sure to call tls_session_update_crypto_params() after calling this
+ * function.
+ */
+static bool
+tls_poor_mans_ncp(struct options *o, const char *remote_ciphername)
+{
+    if (remote_ciphername
+        && tls_item_in_cipher_list(remote_ciphername, o->ncp_ciphers))
+    {
+        o->ciphername = string_alloc(remote_ciphername, &o->gc);
+        msg(D_TLS_DEBUG_LOW, "Using peer cipher '%s'", o->ciphername);
+        return true;
+    }
+    return false;
+}
+
+bool
+check_pull_client_ncp(struct context *c, const int found)
+{
+    if (found & OPT_P_NCP)
+    {
+        msg(D_PUSH, "OPTIONS IMPORT: data channel crypto options modified");
+        return true;
+    }
+
+    if (!c->options.ncp_enabled)
+    {
+        return true;
+    }
+    /* If the server did not push a --cipher, we will switch to the
+     * remote cipher if it is in our ncp-ciphers list */
+    if(tls_poor_mans_ncp(&c->options, c->c2.tls_multi->remote_ciphername))
+    {
+        return true;
+    }
+
+    /* We could not figure out the peer's cipher but we have fallback
+     * enabled */
+    if (!c->c2.tls_multi->remote_ciphername && c->options.enable_ncp_fallback)
+    {
+        return true;
+    }
+
+    /* We failed negotiation, give appropiate error message */
+    if (c->c2.tls_multi->remote_ciphername)
+    {
+        msg(D_TLS_ERRORS, "OPTIONS ERROR: failed to negotiate "
+            "cipher with server.  Add the server's "
+            "cipher ('%s') to --data-ciphers (currently '%s') if "
+            "you want to connect to this server.",
+            c->c2.tls_multi->remote_ciphername,
+            c->options.ncp_ciphers);
+        return false;
+
+    }
+    else
+    {
+        msg(D_TLS_ERRORS, "OPTIONS ERROR: failed to negotiate "
+            "cipher with server. Configure "
+            "--data-ciphers-fallback if you want to connect "
+            "to this server.");
+        return false;
+    }
+}