daemon: added "group" configuration option

The "group" configuration option is similar to "user" as it
sets user set what group MPD shall run as.  With "user"
option, MPD changed GID to the GID of the user, however,
more control could be desired.

Moreover, the patch changes the way of checking whether no
setuid(2)/setgid(2) is required -- previously user names
were compered, now UID and GIDs are compered (ie. the one we
already have (getuid(2)/getgid(2)) with the one we want to
change to).

1 files changed, 31 insertions, 17 deletions

diff --git a/src/daemon.c b/src/daemon.c
index 33b2953a..e7fcd098 100644
--- a/src/daemon.c
+++ b/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;