openssl: support SSLKEYLOGFILE client secret logging

This patch checks for the env var SSLKEYLOGFILE=path, if present, then client connection tls secrets are appended into path.vhostname. This allows decryption of captured encrypted data for debugging purposes. SSKEYLOGFILE=path env var method is the same as provided by Firefox and Chrome for this purpose.
warmcat · Dec 13, 2021 · b8c4820 · b8c4820
1 parent e88a1b1
commit b8c4820
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diff --git a/cmake/lws_config.h.in b/cmake/lws_config.h.in
@@ -93,6 +93,7 @@
 #cmakedefine LWS_HAVE_SSL_CTX_load_verify_dir
 #cmakedefine LWS_HAVE_SSL_CTX_set1_param
 #cmakedefine LWS_HAVE_SSL_CTX_set_ciphersuites
+#cmakedefine LWS_HAVE_SSL_CTX_set_keylog_callback
 #cmakedefine LWS_HAVE_SSL_EXTRA_CHAIN_CERTS
 #cmakedefine LWS_HAVE_SSL_get0_alpn_selected
 #cmakedefine LWS_HAVE_SSL_CTX_EVP_PKEY_new_raw_private_key

diff --git a/lib/core/private-lib-core.h b/lib/core/private-lib-core.h
@@ -426,6 +426,10 @@ struct lws_context {
  #if defined(LWS_WITH_SERVER)
 	char canonical_hostname[96];
  #endif
+#if defined(LWS_HAVE_SSL_CTX_set_keylog_callback) && \
+	defined(LWS_WITH_TLS) && defined(LWS_WITH_CLIENT)
+	char					keylog_file[96];
+#endif
 
 #if defined(LWS_WITH_FILE_OPS)
 	struct lws_plat_file_ops fops_platform;

diff --git a/lib/plat/unix/unix-init.c b/lib/plat/unix/unix-init.c
@@ -178,6 +178,17 @@ lws_plat_init(struct lws_context *context,
 		return 1;
 	}
 
+#if defined(LWS_HAVE_SSL_CTX_set_keylog_callback) && \
+		defined(LWS_WITH_TLS) && defined(LWS_WITH_CLIENT)
+	{
+		char *klf_env = getenv("SSLKEYLOGFILE");
+
+		if (klf_env)
+			lws_strncpy(context->keylog_file, klf_env,
+				sizeof(context->keylog_file));
+	}
+#endif
+
 #if defined(LWS_WITH_PLUGINS) && !defined(LWS_WITH_PLUGINS_BUILTIN)
 	{
 		char *ld_env = getenv("LD_LIBRARY_PATH");

diff --git a/lib/plat/windows/windows-init.c b/lib/plat/windows/windows-init.c
@@ -104,6 +104,17 @@ lws_plat_init(struct lws_context *context,
 	}
 #endif
 
+#if defined(LWS_HAVE_SSL_CTX_set_keylog_callback) && \
+		defined(LWS_WITH_TLS) && defined(LWS_WITH_CLIENT)
+	{
+		char *klf_env = getenv("SSLKEYLOGFILE");
+
+		if (klf_env)
+			lws_strncpy(context->keylog_file, klf_env,
+				sizeof(context->keylog_file));
+	}
+#endif
+
 	for (i = 0; i < FD_HASHTABLE_MODULUS; i++) {
 		context->fd_hashtable[i].wsi =
 			lws_zalloc(sizeof(struct lws*) * context->max_fds,

diff --git a/lib/tls/CMakeLists.txt b/lib/tls/CMakeLists.txt
@@ -344,6 +344,7 @@ CHECK_SYMBOL_EXISTS(${VARIA}SSL_CTX_set_ciphersuites LWS_HAVE_SSL_CTX_set_cipher
 CHECK_FUNCTION_EXISTS(${VARIA}EVP_PKEY_new_raw_private_key LWS_HAVE_EVP_PKEY_new_raw_private_key PARENT_SCOPE)
 CHECK_FUNCTION_EXISTS(${VARIA}SSL_SESSION_set_time LWS_HAVE_SSL_SESSION_set_time PARENT_SCOPE)
 CHECK_SYMBOL_EXISTS(${VARIA}SSL_SESSION_up_ref LWS_HAVE_SSL_SESSION_up_ref PARENT_SCOPE)
+CHECK_FUNCTION_EXISTS(${VARIA}SSL_CTX_set_keylog_callback LWS_HAVE_SSL_CTX_set_keylog_callback PARENT_SCOPE)
 
 
 # deprecated in openssl v3

diff --git a/lib/tls/openssl/openssl-client.c b/lib/tls/openssl/openssl-client.c
@@ -705,6 +705,60 @@ lws_tls_client_vhost_extra_cert_mem(struct lws_vhost *vh,
 	return n != 1;
 }
 
+#if defined(LWS_HAVE_SSL_CTX_set_keylog_callback) && \
+	defined(LWS_WITH_TLS) && defined(LWS_WITH_CLIENT)
+static void
+lws_klog_dump(const SSL *ssl, const char *line)
+{
+	struct lws *wsi = SSL_get_ex_data(ssl,
+					  openssl_websocket_private_data_index);
+	char path[128], hdr[128], ts[64];
+	size_t w = 0, wx = 0;
+	int fd, t;
+
+	if (!wsi || !wsi->a.context->keylog_file[0] || !wsi->a.vhost)
+		return;
+
+	lws_snprintf(path, sizeof(path), "%s.%s", wsi->a.context->keylog_file,
+			wsi->a.vhost->name);
+
+	fd = open(path, O_CREAT | O_RDWR | O_APPEND, 0600);
+	if (fd == -1) {
+		lwsl_vhost_warn(wsi->a.vhost, "Failed to append %s", path);
+		return;
+	}
+
+	/* the first item in the chunk */
+	if (!strncmp(line, "SERVER_HANDSHAKE_TRAFFIC_SECRET", 31)) {
+		w += (size_t)write(fd, "\n# ", 3);
+		wx += 3;
+		t = lwsl_timestamp(LLL_WARN, ts, sizeof(ts));
+		wx += (size_t)t;
+		w += (size_t)write(fd, ts, (size_t)t);
+
+		t = lws_snprintf(hdr, sizeof(hdr), "%s\n", wsi->lc.gutag);
+		w += (size_t)write(fd, hdr, (size_t)t);
+		wx += (size_t)t;
+
+		lwsl_vhost_warn(wsi->a.vhost, "appended ssl keylog: %s", path);
+	}
+
+	wx += strlen(line) + 1;
+	w += (size_t)write(fd, line, 
+#if defined(WIN32)
+			(unsigned int)
+#endif
+			strlen(line));
+	w += (size_t)write(fd, "\n", 1);
+	close(fd);
+
+	if (w != wx) {
+		lwsl_vhost_warn(wsi->a.vhost, "Failed to write %s", path);
+		return;
+	}
+}
+#endif
+
 int
 lws_tls_client_create_vhost_context(struct lws_vhost *vh,
 				    const struct lws_context_creation_info *info,
@@ -887,6 +941,12 @@ lws_tls_client_create_vhost_context(struct lws_vhost *vh,
 
 	vh->tls.tcr = tcr;
 
+#if defined(LWS_HAVE_SSL_CTX_set_keylog_callback) && \
+		defined(LWS_WITH_TLS) && defined(LWS_WITH_CLIENT)
+	if (vh->context->keylog_file[0])
+		SSL_CTX_set_keylog_callback(vh->tls.ssl_client_ctx, lws_klog_dump);
+#endif
+
 #if defined(LWS_WITH_TLS_SESSIONS)
 	vh->tls_session_cache_max = info->tls_session_cache_max ?
 				    info->tls_session_cache_max : 10;