Fix #492: add per-service directories, systemd RuntimeDirectory style

A service that drops privileges cannot create its own PID file in
/run, root owns it.  Finit can create the file with pidfile-create,
but the daemon still cannot touch it to confirm a SIGHUP.

Five new settings, block format only: runtime-dir, state-dir,
cache-dir, logs-dir, and config-dir.  The value is a directory name,
resolved under /run, /var/lib, /var/cache, /var/log, and /etc,
respectively.  The directory is created before the service starts,
mode 0755 owned by user/group, and the full path is exported to the
process as RUNTIME_DIRECTORY, STATE_DIRECTORY, CACHE_DIRECTORY,
LOGS_DIRECTORY, and CONFIGURATION_DIRECTORY.  Mode and ownership are
asserted at creation only, a daemon may tighten them afterwards.

The runtime directory is removed when the unit stops, after any
exec-stop-post script, like systemd with RuntimeDirectoryPreserve=no.
A completed run/task counts as stopped unless remain-after-exit keeps
it up.  The other four persist across restarts.

These are the first settings with no legacy token: they are validated
by service_set_dir() and stored on the svc that service_register()
now returns.  systemd accepts a list of directories per setting; this
is a single name for now, widening later is compatible since
libconfuse accepts a bare value for a list option.

The test sysroot gains libnss_files.so.2, which ldd cannot see, glibc
dlopen()s it.  Without it getpwnam() fails inside the chroot, so
user/group settings never resolved and directory ownership could not
be tested.

Signed-off-by: Joachim Wiberg <troglobit@gmail.com>

src/conf.c

@@ -269,6 +269,11 @@ static cfg_opt_t svc_opts[] = {
 
 	CFG_STR_LIST("capabilities", NULL, CFGF_NODEFAULT),
 	CFG_STR_LIST("caps",         NULL, CFGF_NODEFAULT),	/* alias */
+	CFG_STR     ("runtime-dir",  NULL, CFGF_NODEFAULT),
+	CFG_STR     ("state-dir",    NULL, CFGF_NODEFAULT),
+	CFG_STR     ("cache-dir",    NULL, CFGF_NODEFAULT),
+	CFG_STR     ("logs-dir",     NULL, CFGF_NODEFAULT),
+	CFG_STR     ("config-dir",   NULL, CFGF_NODEFAULT),
 	CFG_STR_LIST("conflicts",    NULL, CFGF_NODEFAULT),
 	CFG_STR     ("if",           NULL, CFGF_NODEFAULT),
 	CFG_STR     ("tty",          NULL, CFGF_NODEFAULT),
@@ -1289,6 +1294,30 @@ static int if_translate(const char *str, char *buf, size_t len, char *file, cons
 	return 0;
 }
 
+/*
+ * These have no legacy token, they are validated by service_set_dir()
+ * and stored directly on the registered svc.  Empty means unset,
+ * service_register() has already cleared the fields.
+ */
+static void dirs_translate(cfg_t *sec, svc_t *svc, char *file)
+{
+	int i;
+
+	for (i = 0; i < NUM_SVCDIRS; i++) {
+		const char *str;
+
+		str = sec_getstr(sec, svcdirs[i].key, NULL);
+		if (!str || !str[0])
+			continue;
+
+		if (service_set_dir(svc, &svcdirs[i], str))
+			logit(LOG_ERR, "%s: %s: %s '%s' %s, ignoring",
+			      file, cfg_title(sec), svcdirs[i].key, str,
+			      errno == ENAMETOOLONG ? "is too long"
+			      : "must be relative, no '..'");
+	}
+}
+
 static void svc_translate(cfg_t *sec, int type, struct rlimit rlimit[], char *file)
 {
 	struct rlimit local_rlimit[RLIMIT_NLIMITS];
@@ -1299,6 +1328,7 @@ static void svc_translate(cfg_t *sec, int type, struct rlimit rlimit[], char *fi
 	long num;
 	char buf[512];
 	char nm[80];
+	svc_t *svc;
 	char *id;
 
 	cmd = sec_getstr(sec, "command", NULL);
@@ -1505,7 +1535,11 @@ static void svc_translate(cfg_t *sec, int type, struct rlimit rlimit[], char *fi
 		addtok(line, sizeof(line), "-- %s", str);
 
 	dbg("translated: %s", line);
-	service_register(type, line, rlimit, file);
+	svc = service_register(type, line, rlimit, file);
+	if (!svc)
+		return;
+
+	dirs_translate(sec, svc, file);
 }
 
 /*

src/service.c

@@ -570,6 +570,101 @@ static void set_uid(uid_t uid, svc_t *svc)
 		err(1, "%s: failed setuid(%d)", svc_ident(svc, NULL, 0), uid);
 }
 
+/*
+ * systemd-style per-service directories: created before each start,
+ * owned by the service user, and exported to the environment.  The
+ * runtime directory is removed again when the service stops, after
+ * any post: script has run.  See issue #492.
+ */
+const struct svcdir svcdirs[NUM_SVCDIRS] = {
+	{ "runtime-dir", "/run",       "RUNTIME_DIRECTORY",       offsetof(svc_t, runtime_dir) },
+	{ "state-dir",   "/var/lib",   "STATE_DIRECTORY",         offsetof(svc_t, state_dir)   },
+	{ "cache-dir",   "/var/cache", "CACHE_DIRECTORY",         offsetof(svc_t, cache_dir)   },
+	{ "logs-dir",    "/var/log",   "LOGS_DIRECTORY",          offsetof(svc_t, logs_dir)    },
+	{ "config-dir",  "/etc",       "CONFIGURATION_DIRECTORY", offsetof(svc_t, config_dir)  },
+};
+
+static char *svcdir_path(svc_t *svc, const struct svcdir *sd, char *path, size_t len)
+{
+	char *name = (char *)svc + sd->off;
+
+	if (!name[0])
+		return NULL;
+
+	paste(path, len, sd->base, name);
+	return path;
+}
+
+/*
+ * Validate and set a per-service directory.  The value is a name
+ * resolved under sd->base, so an absolute path or an escape is
+ * refused with -1 and errno set.
+ */
+int service_set_dir(svc_t *svc, const struct svcdir *sd, const char *name)
+{
+	char *dir = (char *)svc + sd->off;
+
+	if (name[0] == '/' || strstr(name, "..")) {
+		errno = EINVAL;
+		return -1;
+	}
+
+	if (strlcpy(dir, name, MAX_ARG_LEN) >= MAX_ARG_LEN) {
+		dir[0] = 0;
+		errno = ENAMETOOLONG;
+		return -1;
+	}
+
+	return 0;
+}
+
+static void service_mkdirs(svc_t *svc)
+{
+	char path[256];
+	size_t i;
+
+	for (i = 0; i < NELEMS(svcdirs); i++) {
+		char *ptr;
+
+		ptr = svcdir_path(svc, &svcdirs[i], path, sizeof(path));
+		if (!ptr)
+			continue;
+
+		/*
+		 * Script forks land here too, so an existing directory
+		 * is left alone -- mode and ownership are asserted at
+		 * creation only, a daemon may have tightened them.
+		 */
+		if (fisdir(ptr))
+			continue;
+
+		/* only the named directory is chowned, like systemd */
+		mkpath(ptr, 0755);
+		if (mksubsys(ptr, 0755, svc->username, svc->group))
+			logit(LOG_WARNING, "%s: failed creating %s", svc_ident(svc, NULL, 0), ptr);
+	}
+}
+
+static void service_dir_env(svc_t *svc)
+{
+	char path[256];
+	size_t i;
+
+	for (i = 0; i < NELEMS(svcdirs); i++) {
+		if (svcdir_path(svc, &svcdirs[i], path, sizeof(path)))
+			setenv(svcdirs[i].env, path, 1);
+	}
+}
+
+static void service_rmdirs(svc_t *svc)
+{
+	char path[256];
+
+	/* only the runtime directory, /run is tmpfs, the rest persist */
+	if (svcdir_path(svc, &svcdirs[0], path, sizeof(path)))
+		rmrf(path);
+}
+
 static pid_t service_fork(svc_t *svc)
 {
 	const char *cgnm;
@@ -591,6 +686,8 @@ static pid_t service_fork(svc_t *svc)
 
 	if (pid == 0) {
 		char *home = NULL;
+
+		service_mkdirs(svc);
 #ifdef ENABLE_STATIC
 		int uid = 0; /* XXX: Fix better warning that dropprivs is disabled. */
 		int gid = 0;
@@ -664,6 +761,8 @@ static pid_t service_fork(svc_t *svc)
 				err(1, "%s: failed setgid(%d)", svc_ident(svc, NULL, 0), gid);
 		}
 
+		service_dir_env(svc);
+
 		if (uid >= 0) {
 			set_uid(uid, svc);
 
@@ -2272,6 +2371,10 @@ svc_t *service_register(int type, char *cfg, struct rlimit rlimit[], char *file)
 	else
 		memset(svc->capabilities, 0, sizeof(svc->capabilities));
 
+	/* block format only, set by conf.c after registration */
+	for (int i = 0; i < NUM_SVCDIRS; i++)
+		memset((char *)svc + svcdirs[i].off, 0, MAX_ARG_LEN);
+
 	if (!svc_is_tty(svc) && ctty) {
 		char *dev = ctty;
 
@@ -2894,6 +2997,16 @@ static void svc_set_state(svc_t *svc, svc_state_t new_state)
 		return;
 	*state = new_state;
 
+	/*
+	 * The unit has stopped: HALTED comes after any post:/cleanup:
+	 * script, DONE is a completed run/task, where remain-after-exit
+	 * keeps it alive until stopped for real.  Same removal rules as
+	 * systemd RuntimeDirectory with RuntimeDirectoryPreserve=no.
+	 */
+	if (new_state == SVC_HALTED_STATE ||
+	    (new_state == SVC_DONE_STATE && !svc_is_remain(svc)))
+		service_rmdirs(svc);
+
 	if (svc_is_runtask(svc)) {
 		char success[MAX_COND_LEN], failure[MAX_COND_LEN];
 

src/service.h

@@ -27,6 +27,22 @@
 
 #include "svc.h"
 
+/*
+ * systemd-style per-service directories, block format only: the .conf
+ * key, the base the name resolves under, and the environment variable
+ * the path is exported as.  Shared by service.c and conf.c so adding
+ * one means touching the table and svc.h alone.
+ */
+struct svcdir {
+	const char *key;
+	const char *base;
+	const char *env;
+	size_t      off;	/* offsetof() in svc_t */
+};
+#define NUM_SVCDIRS 5
+extern const struct svcdir svcdirs[NUM_SVCDIRS];
+
+int	  service_set_dir	 (svc_t *svc, const struct svcdir *sd, const char *name);
 svc_t	 *service_register	 (int type, char *line, struct rlimit rlimit[], char *file);
 void      service_unregister     (svc_t *svc);
 

src/svc.h

@@ -199,6 +199,14 @@ typedef struct svc {
 	int		       num_supgroups;
 	char	       capabilities[MAX_CMD_LEN];
 
+	/* Directories set up for the service, block format only, the
+	 * name is resolved under a fixed base, e.g. /run/NAME */
+	char	       runtime_dir[MAX_ARG_LEN];
+	char	       state_dir[MAX_ARG_LEN];
+	char	       cache_dir[MAX_ARG_LEN];
+	char	       logs_dir[MAX_ARG_LEN];
+	char	       config_dir[MAX_ARG_LEN];
+
 	/* Command, arguments and service description */
 	char	       cmd[MAX_CMD_LEN];
 	char	       args[MAX_NUM_SVC_ARGS][MAX_CMD_LEN];