daemon: added "group" configuration option

doc/mpdconf.example

@@ -61,6 +61,13 @@
 #
 #user				"nobody"
 #
+# This setting specifies the group that MPD will run as. If not specified
+# primary group of user specified with "user" setting will be used (if set).
+# This is useful if MPD needs to be a member of group such as "audio" to
+# have permission to use sound card.
+#
+#group				"nogroup"
+#
 # This setting sets the address for the daemon to listen on. Careful attention
 # should be paid if this is assigned to anything other then the default, any.
 # This setting can deny access to control of the daemon.

src/conf.c

@@ -61,6 +61,7 @@ static struct config_entry config_entries[] = {
 	{ .name = CONF_PID_FILE, false, false },
 	{ .name = CONF_STATE_FILE, false, false },
 	{ .name = CONF_USER, false, false },
+	{ .name = CONF_GROUP, false, false },
 	{ .name = CONF_BIND_TO_ADDRESS, true, false },
 	{ .name = CONF_PORT, false, false },
 	{ .name = CONF_LOG_LEVEL, false, false },

src/conf.h

@@ -34,6 +34,7 @@
 #define CONF_PID_FILE                   "pid_file"
 #define CONF_STATE_FILE                 "state_file"
 #define CONF_USER                       "user"
+#define CONF_GROUP                      "group"
 #define CONF_BIND_TO_ADDRESS            "bind_to_address"
 #define CONF_PORT                       "port"
 #define CONF_LOG_LEVEL                  "log_level"

src/daemon.c

@@ -45,14 +45,17 @@
 static char *user_name;
 
 /** the Unix user id which MPD runs as */
-static uid_t user_uid;
+static uid_t user_uid = (uid_t)-1;
 
 /** the Unix group id which MPD runs as */
-static gid_t user_gid;
+static gid_t user_gid = (pid_t)-1;
 
 /** the absolute path of the pidfile */
 static char *pidfile;
 
+/* whether "group" conf. option was given */
+static bool had_group = false;
+
 #endif
 
 void
@@ -107,16 +110,19 @@ daemonize_set_user(void)
 	if (user_name == NULL)
 		return;
 
-	/* get uid */
-	if (setgid(user_gid) == -1) {
-		g_error("cannot setgid for user \"%s\": %s",
-			user_name, g_strerror(errno));
+	/* set gid */
+	if (user_gid != (gid_t)-1 && user_gid != getgid()) {
+		if (setgid(user_gid) == -1) {
+			g_error("cannot setgid to %d: %s",
+				(int)user_gid, g_strerror(errno));
+		}
 	}
+
 #ifdef _BSD_SOURCE
 	/* init suplementary groups
 	 * (must be done before we change our uid)
 	 */
-	if (initgroups(user_name, user_gid) == -1) {
+	if (!had_group && initgroups(user_name, user_gid) == -1) {
 		g_warning("cannot init supplementary groups "
 			  "of user \"%s\": %s",
 			  user_name, g_strerror(errno));
@@ -124,7 +130,8 @@ daemonize_set_user(void)
 #endif
 
 	/* set uid */
-	if (setuid(user_uid) == -1) {
+	if (user_uid != (uid_t)-1 && user_uid != getuid() &&
+	    setuid(user_uid) == -1) {
 		g_error("cannot change to uid of user \"%s\": %s",
 			user_name, g_strerror(errno));
 	}
@@ -196,25 +203,32 @@ daemonize(bool detach)
 }
 
 void
-daemonize_init(const char *user, const char *_pidfile)
+daemonize_init(const char *user, const char *group, const char *_pidfile)
 {
 #ifndef WIN32
-	if (user != NULL && strcmp(user, g_get_user_name()) != 0) {
-		struct passwd *pwd;
-
-		user_name = g_strdup(user);
-
-		pwd = getpwnam(user_name);
-		if (pwd == NULL)
-			g_error("no such user \"%s\"", user_name);
+	if (user) {
+		struct passwd *pwd = getpwnam(user);
+		if (!pwd)
+			g_error("no such user \"%s\"", user);
 
 		user_uid = pwd->pw_uid;
 		user_gid = pwd->pw_gid;
 
+		user_name = g_strdup(user);
+
 		/* this is needed by libs such as arts */
 		g_setenv("HOME", pwd->pw_dir, true);
 	}
 
+	if (group) {
+		struct group *grp = grp = getgrnam(group);
+		if (!grp)
+			g_error("no such group \"%s\"", group);
+		user_gid = grp->gr_gid;
+		had_group = true;
+	}
+
+
 	pidfile = g_strdup(_pidfile);
 #else
 	(void)user;

src/daemon.h

@@ -23,7 +23,7 @@
 #include <stdbool.h>
 
 void
-daemonize_init(const char *user, const char *pidfile);
+daemonize_init(const char *user, const char *group, const char *pidfile);
 
 void
 daemonize_finish(void);

src/main.c

@@ -94,6 +94,7 @@ static void
 glue_daemonize_init(const struct options *options)
 {
 	daemonize_init(config_get_string(CONF_USER, NULL),
+		       config_get_string(CONF_GROUP, NULL),
 		       config_get_path(CONF_PID_FILE));
 
 	if (options->kill)