[PATCH v5 3/4] dpp: add support for configuration protocol

James Prestwood
2021-12-17T19:14:50Z

[-- Attachment #1: Type: text/plain, Size: 11803 bytes --]

This is a minimal implementation only supporting legacy network
configuration, i.e. only SSID and PSK/passphrase are supported.

Missing features include:
- Fragmentation/comeback delay support
- DPP AKM support
- 8021x/PKEX support
---
src/dpp.c | 328 ++++++++++++++++++++++++++++++++++++++++++++++++++++++
1 file changed, 328 insertions(+)

v5:
* Updated use of wrap/unwrap APIs
* Added comments about how AAD is used with configuration

diff --git a/src/dpp.c b/src/dpp.c
index dd17cc47..cf322e7d 100644
--- a/src/dpp.c
+++ b/src/dpp.c
@@ -44,6 +44,8 @@
#include "src/crypto.h"
#include "src/mpdu.h"
#include "ell/useful.h"
+#include "src/common.h"
+#include "src/storage.h"

static uint32_t netdev_watch;
static struct l_genl_family *nl80211;
@@ -53,6 +55,7 @@ enum dpp_state {
DPP_STATE_NOTHING,
DPP_STATE_PRESENCE,
DPP_STATE_AUTHENTICATING,
+ DPP_STATE_CONFIGURING,
};

struct dpp_sm {
@@ -84,6 +87,7 @@ struct dpp_sm {
uint8_t auth_addr[6];
uint8_t r_nonce[32];
uint8_t i_nonce[32];
+ uint8_t e_nonce[32];

uint64_t ke[L_ECC_MAX_DIGITS];
uint64_t k2[L_ECC_MAX_DIGITS];
@@ -92,6 +96,8 @@ struct dpp_sm {
struct l_ecc_point *proto_public;

struct l_ecc_point *i_proto_public;
+
+ uint8_t diag_token;
};

static void dpp_free_auth_data(struct dpp_sm *dpp)
@@ -203,6 +209,321 @@ static size_t dpp_build_header(const uint8_t *src, const uint8_t *dest,
return ptr - buf;
}

+static size_t dpp_build_config_header(const uint8_t *src, const uint8_t *dest,
+ uint8_t diag_token,
+ uint8_t buf[static 37])
+{
+ uint8_t *ptr = buf + 24;
+
+ memset(buf, 0, 37);
+
+ l_put_le16(0x00d0, buf);
+ memcpy(buf + 4, dest, 6);
+ memcpy(buf + 10, src, 6);
+ memcpy(buf + 16, broadcast, 6);
+
+ *ptr++ = 0x04; /* Public */
+ *ptr++ = 0x0a; /* Action */
+ *ptr++ = diag_token;
+
+ *ptr++ = IE_TYPE_ADVERTISEMENT_PROTOCOL;
+ *ptr++ = 8; /* len */
+ *ptr++ = 0x00;
+ *ptr++ = IE_TYPE_VENDOR_SPECIFIC;
+ *ptr++ = 5;
+ memcpy(ptr, wifi_alliance_oui, 3);
+ ptr += 3;
+ *ptr++ = 0x1a;
+ *ptr++ = 1;
+
+ return ptr - buf;
+}
+
+/*
+ * The configuration protocols use of AD components is somewhat confusing
+ * since the request/response frames are of a different format than the rest.
+ * In addition there are situations where the components length is zero yet it
+ * is still passed as such to AES-SIV.
+ *
+ * For the configuration request/response frames:
+ *
+ * "AAD for use with AES-SIV for protected messages in the DPP Configuration
+ * protocol shall consist of all octets in the Query Request and Query Response
+ * fields up to the first octet of the Wrapped Data attribute, which is the last
+ * attribute in a DPP Configuration frame. When the number of octets of AAD is
+ * zero, the number of components of AAD passed to AES-SIV is zero."
+ *
+ * - For configuration requests the optional query request field is not
+ * included, therefore no AAD data is passed. (dpp_configuration_start)
+ *
+ * - The configuration response does contain a query response field which is
+ * 5 bytes. (dpp_handle_config_response_frame)
+ *
+ * For the configuration result/status, the same rules are used as the
+ * authentication protocol. This is reiterated in section 6.4.1.
+ *
+ * - For the configuration result there is some confusion as to exactly how the
+ * second AAD component should be passed (since the spec specifically
+ * mentions using two components). There are no attributes prior to the
+ * wrapped data component meaning the length would be zero.
+ * Hostapd/wpa_supplicant pass a zero length AAD component to AES-SIV which
+ * does effect the resulting encryption/decryption so this is also what IWD
+ * will do to remain compliant with it.
+ */
+static void dpp_configuration_start(struct dpp_sm *dpp, const uint8_t *addr)
+{
+ const char *json = "{\"name\":\"IWD\",\"wi-fi_tech\":\"infra\","
+ "\"netRole\":\"sta\"}";
+ struct iovec iov[3];
+ uint8_t hdr[37];
+ uint8_t attrs[512];
+ size_t json_len = strlen(json);
+ uint8_t *ptr = attrs;
+
+ l_getrandom(&dpp->diag_token, 1);
+
+ iov[0].iov_len = dpp_build_config_header(
+ netdev_get_address(dpp->netdev),
+ addr, dpp->diag_token, hdr);
+ iov[0].iov_base = hdr;
+
+ l_getrandom(dpp->e_nonce, dpp->nonce_len);
+
+ /* length */
+ ptr += 2;
+
+ /*
+ * "AAD for use with AES-SIV for protected messages in the DPP
+ * Configuration protocol shall consist of all octets in the Query
+ * Request and Query Response fields up to the first octet of the
+ * Wrapped Data attribute"
+ *
+ * In this case there is no query request/response fields, nor any
+ * attributes besides wrapped data meaning zero AD components.
+ */
+ ptr += dpp_append_wrapped_data(NULL, 0, NULL, 0, ptr, sizeof(attrs),
+ dpp->ke, dpp->key_len, 2,
+ DPP_ATTR_ENROLLEE_NONCE, dpp->nonce_len, dpp->e_nonce,
+ DPP_ATTR_CONFIGURATION_REQUEST, json_len, json);
+
+ l_put_le16(ptr - attrs - 2, attrs);
+
+ iov[1].iov_base = attrs;
+ iov[1].iov_len = ptr - attrs;
+
+ dpp->state = DPP_STATE_CONFIGURING;
+
+ dpp_send_frame(dpp->wdev_id, iov, 2, dpp->current_freq);
+}
+
+static void send_config_result(struct dpp_sm *dpp, const uint8_t *to)
+{
+ uint8_t hdr[32];
+ struct iovec iov[2];
+ uint8_t attrs[256];
+ uint8_t *ptr = attrs;
+ uint8_t zero = 0;
+
+ iov[0].iov_len = dpp_build_header(netdev_get_address(dpp->netdev), to,
+ DPP_FRAME_CONFIGURATION_RESULT, hdr);
+ iov[0].iov_base = hdr;
+
+ ptr += dpp_append_wrapped_data(hdr + 26, 6, attrs, 0, ptr,
+ sizeof(attrs), dpp->ke, dpp->key_len, 2,
+ DPP_ATTR_STATUS, 1, &zero,
+ DPP_ATTR_ENROLLEE_NONCE, dpp->nonce_len, dpp->e_nonce);
+
+ iov[1].iov_base = attrs;
+ iov[1].iov_len = ptr - attrs;
+
+ dpp_send_frame(dpp->wdev_id, iov, 2, dpp->current_freq);
+}
+
+static void dpp_write_config(struct dpp_configuration *config)
+{
+ _auto_(l_free) char *ssid = l_malloc(config->ssid_len + 1);
+ _auto_(l_settings_free) struct l_settings *settings = l_settings_new();
+ _auto_(l_free) char *path;
+
+ memcpy(ssid, config->ssid, config->ssid_len);
+ ssid[config->ssid_len] = '\0';
+
+ path = storage_get_network_file_path(SECURITY_PSK, ssid);
+
+ if (l_settings_load_from_file(settings, path)) {
+ /* Remove any existing Security keys */
+ l_settings_remove_group(settings, "Security");
+ }
+
+ if (config->passphrase)
+ l_settings_set_string(settings, "Security", "Passphrase",
+ config->passphrase);
+ else if (config->psk)
+ l_settings_set_string(settings, "Security", "PreSharedKey",
+ config->psk);
+
+ l_debug("Storing credential for '%s(%s)'", ssid,
+ security_to_str(SECURITY_PSK));
+ storage_network_sync(SECURITY_PSK, ssid, settings);
+}
+
+static void dpp_handle_config_response_frame(const struct mmpdu_header *frame,
+ const void *body, size_t body_len,
+ int rssi, void *user_data)
+{
+ struct dpp_sm *dpp = user_data;
+ const uint8_t *ptr = body;
+ uint16_t status;
+ uint16_t fragmented; /* Fragmented/Comeback delay field */
+ uint8_t adv_protocol_element[] = { 0x6C, 0x08, 0x7F };
+ uint8_t adv_protocol_id[] = { 0xDD, 0x05, 0x50, 0x6F,
+ 0x9A, 0x1A, 0x01 };
+ uint16_t query_len;
+ struct dpp_attr_iter iter;
+ enum dpp_attribute_type type;
+ size_t len;
+ const uint8_t *data;
+ const char *json = NULL;
+ size_t json_len = 0;
+ int dstatus = -1;
+ const uint8_t *wrapped = NULL;
+ const uint8_t *e_nonce = NULL;
+ size_t wrapped_len = 0;
+ _auto_(l_free) uint8_t *unwrapped = NULL;
+ struct dpp_configuration *config;
+ uint8_t ad0[] = { 0x00, 0x10, 0x01, 0x00, 0x05 };
+
+ if (dpp->state != DPP_STATE_CONFIGURING)
+ return;
+
+ ptr += 2;
+
+ /*
+ * Can a configuration request come from someone other than who you
+ * authenticated to?
+ */
+ if (memcmp(dpp->auth_addr, frame->address_2, 6))
+ return;
+
+ if (*ptr++ != dpp->diag_token)
+ return;
+
+ status = l_get_le16(ptr);
+ ptr += 2;
+
+ if (status != 0) {
+ l_debug("Bad configuration status %u", status);
+ return;
+ }
+
+ fragmented = l_get_le16(ptr);
+ ptr += 2;
+
+ /*
+ * TODO: handle 0x0001 (fragmented), as well as comeback delay.
+ */
+ if (fragmented != 0) {
+ l_debug("Fragmented messages not currently supported");
+ return;
+ }
+
+ if (memcmp(ptr, adv_protocol_element, sizeof(adv_protocol_element))) {
+ l_debug("Invalid Advertisement protocol element");
+ return;
+ }
+
+ ptr += sizeof(adv_protocol_element);
+
+ if (memcmp(ptr, adv_protocol_id, sizeof(adv_protocol_id))) {
+ l_debug("Invalid Advertisement protocol ID");
+ return;
+ }
+
+ ptr += sizeof(adv_protocol_id);
+
+ query_len = l_get_le16(ptr);
+ ptr += 2;
+
+ dpp_attr_iter_init(&iter, ptr, query_len);
+
+ while (dpp_attr_iter_next(&iter, &type, &len, &data)) {
+ switch (type) {
+ case DPP_ATTR_STATUS:
+ dstatus = l_get_u8(data);
+ break;
+ case DPP_ATTR_WRAPPED_DATA:
+ wrapped = data;
+ wrapped_len = len;
+ break;
+ default:
+ /*
+ * TODO: CSR Attribute
+ */
+ break;
+ }
+ }
+
+ if (dstatus != DPP_STATUS_OK || !wrapped) {
+ l_debug("Bad status or missing attributes");
+ return;
+ }
+
+ unwrapped = dpp_unwrap_attr(ad0, sizeof(ad0), NULL, 0, dpp->ke,
+ dpp->key_len, wrapped, wrapped_len,
+ &wrapped_len);
+ if (!unwrapped) {
+ l_debug("Failed to unwrap");
+ return;
+ }
+
+ dpp_attr_iter_init(&iter, unwrapped, wrapped_len);
+
+ while (dpp_attr_iter_next(&iter, &type, &len, &data)) {
+ switch (type) {
+ case DPP_ATTR_ENROLLEE_NONCE:
+ if (len != dpp->nonce_len)
+ break;
+
+ if (memcmp(data, dpp->e_nonce, dpp->nonce_len))
+ break;
+
+ e_nonce = data;
+ break;
+ case DPP_ATTR_CONFIGURATION_OBJECT:
+ json = (const char *)data;
+ json_len = len;
+ break;
+ default:
+ break;
+ }
+ }
+
+ if (!json || !e_nonce) {
+ l_debug("No configuration object in response");
+ return;
+ }
+
+ config = dpp_parse_configuration_object(json, json_len);
+ if (!config) {
+ l_error("Configuration object did not parse");
+ return;
+ }
+
+ dpp_write_config(config);
+ /*
+ * TODO: Depending on the info included in the configuration object a
+ * limited scan could be issued to get autoconnect to trigger faster.
+ * In addition this network may already be in past scan results and
+ * could be joined immediately.
+ *
+ * For now just wait for autoconnect.
+ */
+
+ dpp_configuration_free(config);
+
+ send_config_result(dpp, dpp->auth_addr);
+}
+
/*
* The Authentication protocol has a consistent use of AD components, and this
* use is defined in 6.3.1.4:
@@ -407,6 +728,8 @@ static void authenticate_confirm(struct dpp_sm *dpp, const uint8_t *from,

l_debug("Authentication successful");

+ dpp_configuration_start(dpp, from);
+
return;

auth_confirm_failed:
@@ -693,6 +1016,7 @@ static void dpp_create(struct netdev *netdev)
struct l_dbus *dbus = dbus_get_bus();
struct dpp_sm *dpp = l_new(struct dpp_sm, 1);
uint8_t dpp_prefix[] = { 0x04, 0x09, 0x50, 0x6f, 0x9a, 0x1a, 0x01 };
+ uint8_t dpp_conf_response_prefix[] = { 0x04, 0x0b };

dpp->netdev = netdev;
dpp->state = DPP_STATE_NOTHING;
@@ -715,6 +1039,10 @@ static void dpp_create(struct netdev *netdev)
frame_watch_add(netdev_get_wdev_id(netdev), 0, 0x00d0, dpp_prefix,
sizeof(dpp_prefix), dpp_handle_auth_frame,
dpp, NULL);
+ frame_watch_add(netdev_get_wdev_id(netdev), 0, 0x00d0,
+ dpp_conf_response_prefix,
+ sizeof(dpp_conf_response_prefix),
+ dpp_handle_config_response_frame, dpp, NULL);
}

static void dpp_netdev_watch(struct netdev *netdev,
--
2.31.1