rc: new ubus object for handling /etc/init.d/ scripts

This commit adds "rc" ubus object with methods "list" and "exec" for
listing and calling init.d script appropriately. It's useful for all
kind of UIs (e.g. LuCI) and custom apps.

Example:
root@OpenWrt:~# ubus call rc list
{
	"blockd": {
		"start": 80,
		"enabled": true,
		"running": true
	},
	"dnsmasq": {
		"start": 19,
		"enabled": true,
		"running": true
	}
}
root@OpenWrt:~# ubus call rc init '{ "name": "blockd", "action": "disable" }'
root@OpenWrt:~# ubus call rc init '{ "name": "dnsmasq", "action": "stop" }'
root@OpenWrt:~# ubus call rc list
{
	"blockd": {
		"start": 80,
		"enabled": false,
		"running": true
	},
	"dnsmasq": {
		"start": 19,
		"enabled": true,
		"running": false
	}
}

Signed-off-by: Rafał Miłecki <rafal@milecki.pl>
Acked-by: Jo-Philipp Wich <jo@mein.io>

CMakeLists.txt

@@ -38,7 +38,7 @@ INCLUDE_DIRECTORIES(${ubus_include_dir})
 FIND_PATH(ubox_include_dir libubox/blobmsg_json.h)
 INCLUDE_DIRECTORIES(${ubox_include_dir})
 
-ADD_EXECUTABLE(rpcd main.c exec.c session.c uci.c plugin.c)
+ADD_EXECUTABLE(rpcd main.c exec.c session.c uci.c rc.c plugin.c)
 TARGET_LINK_LIBRARIES(rpcd ${ubox} ${ubus} ${uci} ${blobmsg_json} ${json} ${crypt} dl)
 
 SET(PLUGINS "")

include/rpcd/rc.h

@@ -0,0 +1,7 @@
+// SPDX-License-Identifier: ISC OR MIT
+#ifndef __RPCD_RC_H
+#define __RPCD_RC_H
+
+int rpc_rc_api_init(struct ubus_context *ctx);
+
+#endif

main.c

@@ -25,10 +25,11 @@
 #include <signal.h>
 #include <sys/stat.h>
 
+#include <rpcd/exec.h>
+#include <rpcd/plugin.h>
+#include <rpcd/rc.h>
 #include <rpcd/session.h>
 #include <rpcd/uci.h>
-#include <rpcd/plugin.h>
-#include <rpcd/exec.h>
 
 static struct ubus_context *ctx;
 static bool respawn = false;
@@ -113,6 +114,7 @@ int main(int argc, char **argv)
 
 	rpc_session_api_init(ctx);
 	rpc_uci_api_init(ctx);
+	rpc_rc_api_init(ctx);
 	rpc_plugin_api_init(ctx);
 
 	hangup = getenv("RPC_HANGUP");

rc.c

@@ -0,0 +1,363 @@
+// SPDX-License-Identifier: ISC OR MIT
+/*
+ * rpcd - UBUS RPC server
+ *
+ * Copyright (C) 2020 Rafał Miłecki <rafal@milecki.pl>
+ */
+
+#include <dirent.h>
+#include <fcntl.h>
+#include <linux/limits.h>
+#include <sys/stat.h>
+#include <sys/wait.h>
+
+#include <libubox/blobmsg.h>
+#include <libubox/ulog.h>
+#include <libubox/uloop.h>
+#include <libubus.h>
+
+#include <rpcd/rc.h>
+
+#define RC_LIST_EXEC_TIMEOUT_MS			3000
+
+enum {
+	RC_INIT_NAME,
+	RC_INIT_ACTION,
+	__RC_INIT_MAX
+};
+
+static const struct blobmsg_policy rc_init_policy[] = {
+	[RC_INIT_NAME] = { "name", BLOBMSG_TYPE_STRING },
+	[RC_INIT_ACTION] = { "action", BLOBMSG_TYPE_STRING },
+};
+
+struct rc_list_context {
+	struct uloop_process process;
+	struct uloop_timeout timeout;
+	struct ubus_context *ctx;
+	struct ubus_request_data req;
+	struct blob_buf *buf;
+	DIR *dir;
+
+	/* Info about currently processed init.d entry */
+	struct {
+		char path[PATH_MAX];
+		const char *d_name;
+		unsigned int start;
+		unsigned int stop;
+		bool enabled;
+		bool running;
+	} entry;
+};
+
+static void rc_list_readdir(struct rc_list_context *c);
+
+/**
+ * rc_check_script - check if script is safe to execute as root
+ *
+ * Check if it's owned by root and if only root can modify it.
+ */
+static int rc_check_script(const char *path)
+{
+	struct stat s;
+
+	if (stat(path, &s))
+		return UBUS_STATUS_NOT_FOUND;
+
+	if (s.st_uid != 0 || s.st_gid != 0 || !(s.st_mode & S_IXUSR) || (s.st_mode & S_IWOTH))
+		return UBUS_STATUS_PERMISSION_DENIED;
+
+	return UBUS_STATUS_OK;
+}
+
+static void rc_list_add_table(struct rc_list_context *c)
+{
+	void *e;
+
+	e = blobmsg_open_table(c->buf, c->entry.d_name);
+
+	if (c->entry.start)
+		blobmsg_add_u16(c->buf, "start", c->entry.start);
+	if (c->entry.stop)
+		blobmsg_add_u16(c->buf, "stop", c->entry.stop);
+	blobmsg_add_u8(c->buf, "enabled", c->entry.enabled);
+	blobmsg_add_u8(c->buf, "running", c->entry.running);
+
+	blobmsg_close_table(c->buf, e);
+}
+
+static void rpc_list_exec_timeout_cb(struct uloop_timeout *t)
+{
+	struct rc_list_context *c = container_of(t, struct rc_list_context, timeout);
+
+	ULOG_WARN("Timeout waiting for %s\n", c->entry.path);
+
+	uloop_process_delete(&c->process);
+	kill(c->process.pid, SIGKILL);
+
+	rc_list_readdir(c);
+}
+
+/**
+ * rc_exec - execute a file and call callback on complete
+ */
+static int rc_list_exec(struct rc_list_context *c, const char *action, uloop_process_handler cb)
+{
+	pid_t pid;
+	int err;
+	int fd;
+
+	pid = fork();
+	switch (pid) {
+	case -1:
+		return -errno;
+	case 0:
+		/* Set stdin, stdout & stderr to /dev/null */
+		fd = open("/dev/null", O_RDWR);
+		if (fd >= 0) {
+			dup2(fd, 0);
+			dup2(fd, 1);
+			dup2(fd, 2);
+			if (fd > 2)
+				close(fd);
+		}
+
+		uloop_end();
+
+		execl(c->entry.path, c->entry.path, action, NULL);
+		exit(errno);
+	default:
+		c->process.pid = pid;
+		c->process.cb = cb;
+
+		err = uloop_process_add(&c->process);
+		if (err)
+			return err;
+
+		c->timeout.cb = rpc_list_exec_timeout_cb;
+		err = uloop_timeout_set(&c->timeout, RC_LIST_EXEC_TIMEOUT_MS);
+		if (err) {
+			uloop_process_delete(&c->process);
+			return err;
+		}
+
+		return 0;
+	}
+}
+
+static void rc_list_exec_running_cb(struct uloop_process *p, int stat)
+{
+	struct rc_list_context *c = container_of(p, struct rc_list_context, process);
+
+	uloop_timeout_cancel(&c->timeout);
+
+	c->entry.running = !stat;
+	rc_list_add_table(c);
+
+	rc_list_readdir(c);
+}
+
+static void rc_list_readdir(struct rc_list_context *c)
+{
+	struct dirent *e;
+	FILE *fp;
+
+	e = readdir(c->dir);
+	if (!e) {
+		closedir(c->dir);
+		ubus_send_reply(c->ctx, &c->req, c->buf->head);
+		ubus_complete_deferred_request(c->ctx, &c->req, UBUS_STATUS_OK);
+		return;
+	}
+
+	if (!strcmp(e->d_name, ".") || !strcmp(e->d_name, ".."))
+		goto next;
+
+	memset(&c->entry, 0, sizeof(c->entry));
+
+	snprintf(c->entry.path, sizeof(c->entry.path), "/etc/init.d/%s", e->d_name);
+	if (rc_check_script(c->entry.path))
+		goto next;
+
+	c->entry.d_name = e->d_name;
+
+	fp = fopen(c->entry.path, "r");
+	if (fp) {
+		struct stat s;
+		char path[PATH_MAX];
+		char line[32];
+		bool beginning;
+
+		beginning = true;
+		while (!c->entry.start && !c->entry.stop && fgets(line, sizeof(line), fp)) {
+			if (beginning) {
+				if (!strncmp(line, "START=", 6)) {
+					c->entry.start = strtoul(line + 6, NULL, 0);
+				} else if (!strncmp(line, "STOP=", 5)) {
+					c->entry.stop = strtoul(line + 5, NULL, 0);
+				}
+			}
+
+			beginning = !!strchr(line, '\n');
+		}
+		fclose(fp);
+
+		snprintf(path, sizeof(path), "/etc/rc.d/S%02d%s", c->entry.start, c->entry.d_name);
+		if (!stat(path, &s) && (s.st_mode & S_IXUSR))
+			c->entry.enabled = true;
+	}
+
+	if (rc_list_exec(c, "running", rc_list_exec_running_cb))
+		goto next;
+
+	return;
+next:
+	rc_list_readdir(c);
+}
+
+/**
+ * rc_list - allocate listing context and start reading directory
+ */
+static int rc_list(struct ubus_context *ctx, struct ubus_object *obj,
+		   struct ubus_request_data *req, const char *method,
+		   struct blob_attr *msg)
+{
+	static struct blob_buf buf;
+	struct rc_list_context *c;
+
+	blob_buf_init(&buf, 0);
+
+	c = calloc(1, sizeof(*c));
+	if (!c)
+		return UBUS_STATUS_UNKNOWN_ERROR;
+
+	c->ctx = ctx;
+	c->buf = &buf;
+	c->dir = opendir("/etc/init.d");
+	if (!c->dir) {
+		free(c);
+		return UBUS_STATUS_UNKNOWN_ERROR;
+	}
+
+	ubus_defer_request(ctx, req, &c->req);
+
+	rc_list_readdir(c);
+
+	return 0; /* Deferred */
+}
+
+struct rc_init_context {
+	struct uloop_process process;
+	struct ubus_context *ctx;
+	struct ubus_request_data req;
+};
+
+static void rc_init_cb(struct uloop_process *p, int stat)
+{
+	struct rc_init_context *c = container_of(p, struct rc_init_context, process);
+
+	ubus_complete_deferred_request(c->ctx, &c->req, UBUS_STATUS_OK);
+
+	free(c);
+}
+
+static int rc_init(struct ubus_context *ctx, struct ubus_object *obj,
+		   struct ubus_request_data *req, const char *method,
+		   struct blob_attr *msg)
+{
+	struct blob_attr *tb[__RC_INIT_MAX];
+	struct rc_init_context *c;
+	char path[PATH_MAX];
+	const char *action;
+	const char *name;
+	const char *chr;
+	pid_t pid;
+	int err;
+	int fd;
+
+	blobmsg_parse(rc_init_policy, __RC_INIT_MAX, tb, blobmsg_data(msg), blobmsg_data_len(msg));
+
+	if (!tb[RC_INIT_NAME] || !tb[RC_INIT_ACTION])
+		return UBUS_STATUS_INVALID_ARGUMENT;
+
+	name = blobmsg_get_string(tb[RC_INIT_NAME]);
+
+	/* Validate script name */
+	for (chr = name; (chr = strchr(chr, '.')); chr++) {
+		if (*(chr + 1) == '.')
+			return UBUS_STATUS_INVALID_ARGUMENT;
+	}
+	if (strchr(name, '/'))
+		return UBUS_STATUS_INVALID_ARGUMENT;
+
+	snprintf(path, sizeof(path), "/etc/init.d/%s", name);
+
+	/* Validate script privileges */
+	err = rc_check_script(path);
+	if (err)
+		return err;
+
+	action = blobmsg_get_string(tb[RC_INIT_ACTION]);
+	if (strcmp(action, "disable") &&
+	    strcmp(action, "enable") &&
+	    strcmp(action, "stop") &&
+	    strcmp(action, "start") &&
+	    strcmp(action, "restart") &&
+	    strcmp(action, "reload"))
+		return UBUS_STATUS_INVALID_ARGUMENT;
+
+	c = calloc(1, sizeof(*c));
+	if (!c)
+		return UBUS_STATUS_UNKNOWN_ERROR;
+
+	pid = fork();
+	switch (pid) {
+	case -1:
+		free(c);
+		return UBUS_STATUS_UNKNOWN_ERROR;
+	case 0:
+		/* Set stdin, stdout & stderr to /dev/null */
+		fd = open("/dev/null", O_RDWR);
+		if (fd >= 0) {
+			dup2(fd, 0);
+			dup2(fd, 1);
+			dup2(fd, 2);
+			if (fd > 2)
+				close(fd);
+		}
+
+		uloop_end();
+
+		execl(path, path, action, NULL);
+		exit(errno);
+	default:
+		c->ctx = ctx;
+		c->process.pid = pid;
+		c->process.cb = rc_init_cb;
+		uloop_process_add(&c->process);
+
+		ubus_defer_request(ctx, req, &c->req);
+
+		return 0; /* Deferred */
+	}
+}
+
+int rpc_rc_api_init(struct ubus_context *ctx)
+{
+	static const struct ubus_method rc_methods[] = {
+		UBUS_METHOD_NOARG("list", rc_list),
+		UBUS_METHOD("init", rc_init, rc_init_policy),
+	};
+
+	static struct ubus_object_type rc_type =
+		UBUS_OBJECT_TYPE("rc", rc_methods);
+
+	static struct ubus_object obj = {
+		.name = "rc",
+		.type = &rc_type,
+		.methods = rc_methods,
+		.n_methods = ARRAY_SIZE(rc_methods),
+	};
+
+	return ubus_add_object(ctx, &obj);
+}