Merge branch 'debian/experimental-2.5'

1 files changed, 408 insertions, 0 deletions

diff --git a/src/openvpn/auth_token.c b/src/openvpn/auth_token.c
new file mode 100644
index 0000000..cc70c06
--- /dev/null
+++ b/src/openvpn/auth_token.c
@@ -0,0 +1,408 @@
+#ifdef HAVE_CONFIG_H
+#include "config.h"
+#elif defined(_MSC_VER)
+#include "config-msvc.h"
+#endif
+
+#include "syshead.h"
+
+#include "base64.h"
+#include "buffer.h"
+#include "crypto.h"
+#include "openvpn.h"
+#include "ssl_common.h"
+#include "auth_token.h"
+#include "push.h"
+#include "integer.h"
+#include "ssl.h"
+#include "ssl_verify.h"
+#include <inttypes.h>
+
+const char *auth_token_pem_name = "OpenVPN auth-token server key";
+
+#define AUTH_TOKEN_SESSION_ID_LEN 12
+#if AUTH_TOKEN_SESSION_ID_LEN % 3
+#error AUTH_TOKEN_SESSION_ID_LEN needs to be multiple a 3
+#endif
+
+/* Size of the data of the token (not b64 encoded and without prefix) */
+#define TOKEN_DATA_LEN (2 * sizeof(int64_t) + AUTH_TOKEN_SESSION_ID_LEN + 32)
+
+static struct key_type
+auth_token_kt(void)
+{
+    struct key_type kt = { 0 };
+    /* We do not encrypt our session tokens */
+    kt.cipher = NULL;
+    kt.digest = md_kt_get("SHA256");
+
+    if (!kt.digest)
+    {
+        msg(M_WARN, "ERROR: --tls-crypt requires HMAC-SHA-256 support.");
+        return (struct key_type) { 0 };
+    }
+
+    kt.hmac_length = md_kt_size(kt.digest);
+
+    return kt;
+}
+
+
+void
+add_session_token_env(struct tls_session *session, struct tls_multi *multi,
+                      const struct user_pass *up)
+{
+    if (!multi->opt.auth_token_generate)
+    {
+        return;
+    }
+
+
+    const char *state;
+
+    if (!is_auth_token(up->password))
+    {
+        state = "Initial";
+    }
+    else if (multi->auth_token_state_flags & AUTH_TOKEN_HMAC_OK)
+    {
+        switch (multi->auth_token_state_flags & (AUTH_TOKEN_VALID_EMPTYUSER|AUTH_TOKEN_EXPIRED))
+        {
+            case 0:
+                state = "Authenticated";
+                break;
+
+            case AUTH_TOKEN_EXPIRED:
+                state = "Expired";
+                break;
+
+            case AUTH_TOKEN_VALID_EMPTYUSER:
+                state = "AuthenticatedEmptyUser";
+                break;
+
+            case AUTH_TOKEN_VALID_EMPTYUSER | AUTH_TOKEN_EXPIRED:
+                state = "ExpiredEmptyUser";
+                break;
+
+            default:
+                /* Silence compiler warning, all four possible combinations are covered */
+                ASSERT(0);
+        }
+    }
+    else
+    {
+        state = "Invalid";
+    }
+
+    setenv_str(session->opt->es, "session_state", state);
+
+    /* We had a valid session id before */
+    const char *session_id_source;
+    if (multi->auth_token_state_flags & AUTH_TOKEN_HMAC_OK
+        &!(multi->auth_token_state_flags & AUTH_TOKEN_EXPIRED))
+    {
+        session_id_source = up->password;
+    }
+    else
+    {
+        /*
+         * No session before, generate a new session token for the new session
+         */
+        if (!multi->auth_token)
+        {
+            generate_auth_token(up, multi);
+        }
+        session_id_source = multi->auth_token;
+    }
+    /*
+     * In the auth-token the auth token is already base64 encoded
+     * and being a multiple of 4 ensure that it a multiple of bytes
+     * in the encoding
+     */
+
+    char session_id[AUTH_TOKEN_SESSION_ID_LEN*2] = {0};
+    memcpy(session_id, session_id_source + strlen(SESSION_ID_PREFIX),
+           AUTH_TOKEN_SESSION_ID_LEN*8/6);
+
+    setenv_str(session->opt->es, "session_id", session_id);
+}
+
+void
+auth_token_write_server_key_file(const char *filename)
+{
+    write_pem_key_file(filename, auth_token_pem_name);
+}
+
+void
+auth_token_init_secret(struct key_ctx *key_ctx, const char *key_file,
+                       bool key_inline)
+{
+    struct key_type kt = auth_token_kt();
+
+    struct buffer server_secret_key = alloc_buf(2048);
+
+    bool key_loaded = false;
+    if (key_file)
+    {
+        key_loaded = read_pem_key_file(&server_secret_key,
+                                       auth_token_pem_name,
+                                       key_file, key_inline);
+    }
+    else
+    {
+        key_loaded = generate_ephemeral_key(&server_secret_key,
+                                            auth_token_pem_name);
+    }
+
+    if (!key_loaded)
+    {
+        msg(M_FATAL, "ERROR: Cannot load auth-token secret");
+    }
+
+    struct key key;
+
+    if (!buf_read(&server_secret_key, &key, sizeof(key)))
+    {
+        msg(M_FATAL, "ERROR: not enough data in auth-token secret");
+    }
+    init_key_ctx(key_ctx, &key, &kt, false, "auth-token secret");
+
+    free_buf(&server_secret_key);
+}
+
+void
+generate_auth_token(const struct user_pass *up, struct tls_multi *multi)
+{
+    struct gc_arena gc = gc_new();
+
+    int64_t timestamp = htonll((uint64_t)now);
+    int64_t initial_timestamp = timestamp;
+
+    hmac_ctx_t *ctx = multi->opt.auth_token_key.hmac;
+    ASSERT(hmac_ctx_size(ctx) == 256/8);
+
+    uint8_t sessid[AUTH_TOKEN_SESSION_ID_LEN];
+
+    if (multi->auth_token)
+    {
+        /* Just enough space to fit 8 bytes+ 1 extra to decode a non padded
+         * base64 string (multiple of 3 bytes). 9 bytes => 12 bytes base64
+         * bytes
+         */
+        char old_tstamp_decode[9];
+
+        /*
+         * reuse the same session id and timestamp and null terminate it at
+         * for base64 decode it only decodes the session id part of it
+         */
+        char *old_sessid = multi->auth_token + strlen(SESSION_ID_PREFIX);
+        char *old_tsamp_initial = old_sessid + AUTH_TOKEN_SESSION_ID_LEN*8/6;
+
+        old_tsamp_initial[12] = '\0';
+        ASSERT(openvpn_base64_decode(old_tsamp_initial, old_tstamp_decode, 9) == 9);
+
+        /*
+         * Avoid old gcc (4.8.x) complaining about strict aliasing
+         * by using a temporary variable instead of doing it in one
+         * line
+         */
+        uint64_t *tstamp_ptr = (uint64_t *) old_tstamp_decode;
+        initial_timestamp = *tstamp_ptr;
+
+        old_tsamp_initial[0] = '\0';
+        ASSERT(openvpn_base64_decode(old_sessid, sessid, AUTH_TOKEN_SESSION_ID_LEN)==AUTH_TOKEN_SESSION_ID_LEN);
+
+
+        /* free the auth-token, we will replace it with a new one */
+        free(multi->auth_token);
+    }
+    else if (!rand_bytes(sessid, AUTH_TOKEN_SESSION_ID_LEN))
+    {
+        msg( M_FATAL, "Failed to get enough randomness for "
+             "authentication token");
+    }
+
+    /* Calculate the HMAC */
+    /* We enforce up->username to be \0 terminated in ssl.c.. Allowing username
+     * with \0 in them is asking for troubles in so many ways anyway that we
+     * ignore that corner case here
+     */
+    uint8_t hmac_output[256/8];
+
+    hmac_ctx_reset(ctx);
+
+    /*
+     * If the token was only valid for the empty user, also generate
+     * a new token with the empty username since we do not want to loose
+     * the information that the username cannot be trusted
+     */
+    if (multi->auth_token_state_flags & AUTH_TOKEN_VALID_EMPTYUSER)
+    {
+        hmac_ctx_update(ctx, (const uint8_t *) "", 0);
+    }
+    else
+    {
+        hmac_ctx_update(ctx, (uint8_t *) up->username, (int) strlen(up->username));
+    }
+    hmac_ctx_update(ctx, sessid, AUTH_TOKEN_SESSION_ID_LEN);
+    hmac_ctx_update(ctx, (uint8_t *) &initial_timestamp, sizeof(initial_timestamp));
+    hmac_ctx_update(ctx, (uint8_t *) &timestamp, sizeof(timestamp));
+    hmac_ctx_final(ctx, hmac_output);
+
+    /* Construct the unencoded session token */
+    struct buffer token = alloc_buf_gc(
+        2*sizeof(uint64_t) + AUTH_TOKEN_SESSION_ID_LEN + 256/8, &gc);
+
+    ASSERT(buf_write(&token, sessid, sizeof(sessid)));
+    ASSERT(buf_write(&token, &initial_timestamp, sizeof(initial_timestamp)));
+    ASSERT(buf_write(&token, &timestamp, sizeof(timestamp)));
+    ASSERT(buf_write(&token, hmac_output, sizeof(hmac_output)));
+
+    char *b64output;
+    openvpn_base64_encode(BPTR(&token), BLEN(&token), &b64output);
+
+    struct buffer session_token = alloc_buf_gc(
+        strlen(SESSION_ID_PREFIX) + strlen(b64output) + 1, &gc);
+
+    ASSERT(buf_write(&session_token, SESSION_ID_PREFIX, strlen(SESSION_ID_PREFIX)));
+    ASSERT(buf_write(&session_token, b64output, (int)strlen(b64output)));
+    ASSERT(buf_write_u8(&session_token, 0));
+
+    free(b64output);
+
+    multi->auth_token = strdup((char *)BPTR(&session_token));
+
+    dmsg(D_SHOW_KEYS, "Generated token for client: %s (%s)",
+         multi->auth_token, up->username);
+
+    gc_free(&gc);
+}
+
+
+static bool
+check_hmac_token(hmac_ctx_t *ctx, const uint8_t *b64decoded, const char *username)
+{
+    ASSERT(hmac_ctx_size(ctx) == 256/8);
+
+    uint8_t hmac_output[256/8];
+
+    hmac_ctx_reset(ctx);
+    hmac_ctx_update(ctx, (uint8_t *) username, (int)strlen(username));
+    hmac_ctx_update(ctx, b64decoded, TOKEN_DATA_LEN - 256/8);
+    hmac_ctx_final(ctx, hmac_output);
+
+    const uint8_t *hmac = b64decoded + TOKEN_DATA_LEN - 256/8;
+    return memcmp_constant_time(&hmac_output, hmac, 32) == 0;
+}
+
+unsigned int
+verify_auth_token(struct user_pass *up, struct tls_multi *multi,
+                  struct tls_session *session)
+{
+    /*
+     * Base64 is <= input and input is < USER_PASS_LEN, so using USER_PASS_LEN
+     * is safe here but a bit overkill
+     */
+    uint8_t b64decoded[USER_PASS_LEN];
+    int decoded_len = openvpn_base64_decode(up->password + strlen(SESSION_ID_PREFIX),
+                                            b64decoded, USER_PASS_LEN);
+
+    /*
+     * Ensure that the decoded data is the size of the
+     * timestamp + hmac + session id
+     */
+    if (decoded_len != TOKEN_DATA_LEN)
+    {
+        msg(M_WARN, "ERROR: --auth-token wrong size (%d!=%d)",
+            decoded_len, (int) TOKEN_DATA_LEN);
+        return 0;
+    }
+
+    unsigned int ret = 0;
+
+    const uint8_t *sessid = b64decoded;
+    const uint8_t *tstamp_initial = sessid + AUTH_TOKEN_SESSION_ID_LEN;
+    const uint8_t *tstamp = tstamp_initial + sizeof(int64_t);
+
+    uint64_t timestamp = ntohll(*((uint64_t *) (tstamp)));
+    uint64_t timestamp_initial = ntohll(*((uint64_t *) (tstamp_initial)));
+
+    hmac_ctx_t *ctx = multi->opt.auth_token_key.hmac;
+    if (check_hmac_token(ctx, b64decoded, up->username))
+    {
+        ret |= AUTH_TOKEN_HMAC_OK;
+    }
+    else if (check_hmac_token(ctx, b64decoded, ""))
+    {
+        ret |= AUTH_TOKEN_HMAC_OK;
+        ret |= AUTH_TOKEN_VALID_EMPTYUSER;
+        /* overwrite the username of the client with the empty one */
+        strcpy(up->username, "");
+    }
+    else
+    {
+        msg(M_WARN, "--auth-token-gen: HMAC on token from client failed (%s)",
+            up->username);
+        return 0;
+    }
+
+    /* Accept session tokens that not expired are in the acceptable range
+     * for renogiations */
+    bool in_renog_time = now >= timestamp
+                         && now < timestamp + 2 * session->opt->renegotiate_seconds;
+
+    /* We could still have a client that does not update
+     * its auth-token, so also allow the initial auth-token */
+    bool initialtoken = multi->auth_token_initial
+                        && memcmp_constant_time(up->password, multi->auth_token_initial,
+                                                strlen(multi->auth_token_initial)) == 0;
+
+    if (!in_renog_time && !initialtoken)
+    {
+        ret |= AUTH_TOKEN_EXPIRED;
+    }
+
+    /* Sanity check the initial timestamp */
+    if (timestamp < timestamp_initial)
+    {
+        msg(M_WARN, "Initial timestamp (%" PRIu64 " in token from client earlier than "
+            "current timestamp %" PRIu64 ". Broken/unsynchronised clock?",
+            timestamp_initial, timestamp);
+        ret |= AUTH_TOKEN_EXPIRED;
+    }
+
+    if (multi->opt.auth_token_lifetime
+        && now > timestamp_initial + multi->opt.auth_token_lifetime)
+    {
+        ret |= AUTH_TOKEN_EXPIRED;
+    }
+
+    if (ret & AUTH_TOKEN_EXPIRED)
+    {
+        /* Tell client that the session token is expired */
+        auth_set_client_reason(multi, "SESSION: token expired");
+        msg(M_INFO, "--auth-token-gen: auth-token from client expired");
+    }
+    return ret;
+}
+
+void
+wipe_auth_token(struct tls_multi *multi)
+{
+    if (multi)
+    {
+        if (multi->auth_token)
+        {
+            secure_memzero(multi->auth_token, strlen(multi->auth_token));
+            free(multi->auth_token);
+        }
+        if (multi->auth_token_initial)
+        {
+            secure_memzero(multi->auth_token_initial,
+                           strlen(multi->auth_token_initial));
+            free(multi->auth_token_initial);
+        }
+        multi->auth_token = NULL;
+        multi->auth_token_initial = NULL;
+    }
+}