session: support reclaiming pending apply session

Reclaim the pending apply session upon login when the username matches the
current login.

This is required to support apply-confirm-rollback workflow for ubus browser
clients, since changing IPs requires re-login to the device due to cross
domain restrictions.

Signed-off-by: Jo-Philipp Wich <jo@mein.io>

include/rpcd/session.h

@@ -36,6 +36,8 @@
 #define RPC_SESSION_DIRECTORY	"/var/run/rpcd/sessions"
 #define RPC_SESSION_ACL_DIR		"/usr/share/rpcd/acl.d"
 
+extern char apply_sid[RPC_SID_LEN + 1];
+
 struct rpc_session {
 	struct avl_node avl;
 	char id[RPC_SID_LEN + 1];

session.c

@@ -1085,6 +1085,31 @@ rpc_login_setup_acls(struct rpc_session *ses, struct uci_section *login)
 	globfree(&gl);
 }
 
+static struct rpc_session *
+rpc_reclaim_apply_session(const char *expected_username)
+{
+	struct rpc_session_data *username;
+	struct rpc_session *ses;
+
+	if (!apply_sid[0])
+		return NULL;
+
+	ses = rpc_session_get(apply_sid);
+
+	if (!ses)
+		return NULL;
+
+	username = avl_find_element(&ses->data, "username", username, avl);
+
+	if (!username || blobmsg_type(username->attr) != BLOBMSG_TYPE_STRING)
+		return NULL;
+
+	if (strcmp(blobmsg_get_string(username->attr), expected_username))
+		return NULL;
+
+	return ses;
+}
+
 static int
 rpc_handle_login(struct ubus_context *ctx, struct ubus_object *obj,
                  struct ubus_request_data *req, const char *method,
@@ -1122,7 +1147,15 @@ rpc_handle_login(struct ubus_context *ctx, struct ubus_object *obj,
 	if (tb[RPC_L_TIMEOUT])
 		timeout = blobmsg_get_u32(tb[RPC_L_TIMEOUT]);
 
-	ses = rpc_session_create(timeout);
+	/*
+	 * attempt to reclaim a pending apply session, but only accept it
+	 * if the username matches, otherwise perform a new login
+	 */
+
+	ses = rpc_reclaim_apply_session(blobmsg_get_string(tb[RPC_L_USERNAME]));
+
+	if (!ses)
+		ses = rpc_session_create(timeout);
 
 	if (!ses) {
 		rv = UBUS_STATUS_UNKNOWN_ERROR;

uci.c

@@ -30,7 +30,8 @@ static struct blob_buf buf;
 static struct uci_context *cursor;
 static struct uloop_timeout apply_timer;
 static struct ubus_context *apply_ctx;
-static char apply_sid[RPC_SID_LEN + 1];
+
+char apply_sid[RPC_SID_LEN + 1];
 
 enum {
 	RPC_G_CONFIG,