Add support for dropping privileges to a specified user and/or group.

PR:		108523
Submitted by:	Dmitri Alenitchev <dmitri@dworlds.ru> (original version)
Reviewed by:	mpp (first reply to PR)

usr.sbin/daemon/daemon.8

@@ -26,7 +26,7 @@
 .\"
 .\" $FreeBSD$
 .\"
-.Dd August 30, 2001
+.Dd March 9, 2007
 .Dt DAEMON 8
 .Os
 .Sh NAME
@@ -35,6 +35,8 @@
 .Sh SYNOPSIS
 .Nm
 .Op Fl cf
+.Op Fl u Ar user
+.Op Fl g Ar group
 .Op Fl p Ar pidfile
 .Ar command arguments ...
 .Sh DESCRIPTION
@@ -42,6 +44,7 @@ The
 .Nm
 utility detaches itself from the controlling terminal and
 executes the program specified by its arguments.
+Privileges may be lowered to specified user and/or group.
 .Pp
 The options are as follows:
 .Bl -tag -width indent
@@ -51,10 +54,14 @@ Change the current working directory to the root
 .It Fl f
 Redirect standard input, standard output and standard error to
 .Pa /dev/null .
+.It Fl g Ar group
+Drop privileges to specified group.
 .It Fl p Ar file
 Write the ID of the created process into the
 .Ar file
 using
+.It Fl u Ar user
+Drop privileges to specified user.
 .Xr pidfile 3
 functionality.
 Note, that the file will be created shortly before the process is
@@ -77,6 +84,8 @@ standard error unless the
 .Fl f
 flag is specified.
 .Sh SEE ALSO
+.Xr setregid 2 ,
+.Xr setreuid 2 ,
 .Xr daemon 3 ,
 .Xr exec 3 ,
 .Xr pidfile 3 ,

usr.sbin/daemon/daemon.c

@@ -35,11 +35,14 @@ __FBSDID("$FreeBSD$");
 
 #include <err.h>
 #include <errno.h>
+#include <pwd.h>
+#include <grp.h>
 #include <libutil.h>
 #include <stdio.h>
 #include <stdlib.h>
 #include <unistd.h>
 
+static void restrict_process(const char *, const char *);
 static void usage(void);
 
 int
@@ -47,12 +50,12 @@ main(int argc, char *argv[])
 {
 	struct pidfh *pfh;
 	int ch, nochdir, noclose, errcode;
-	const char *pidfile;
+	const char *pidfile, *user, *group;
 	pid_t otherpid;
 
 	nochdir = noclose = 1;
-	pidfile = NULL;
+	pidfile = user = group = NULL;
-	while ((ch = getopt(argc, argv, "-cfp:")) != -1) {
+	while ((ch = getopt(argc, argv, "-cfg:p:u:")) != -1) {
 		switch (ch) {
 		case 'c':
 			nochdir = 0;
@@ -60,6 +63,12 @@ main(int argc, char *argv[])
 		case 'f':
 			noclose = 0;
 			break;
+		case 'u':
+			user = optarg;
+			break;
+		case 'g':
+			group = optarg;
+			break;
 		case 'p':
 			pidfile = optarg;
 			break;
@@ -72,6 +81,14 @@ main(int argc, char *argv[])
 
 	if (argc == 0)
 		usage();
+
+	if (user || group) {
+		if (getuid() != 0)
+			errx(1, "only root user is allowed to chroot "
+			    "and change UID/GID");
+		restrict_process(user, group);
+	}
+
 	/*
 	 * Try to open the pidfile before calling daemon(3),
 	 * to be able to report the error intelligently
@@ -108,10 +125,35 @@ main(int argc, char *argv[])
 	errc(1, errcode, "%s", argv[0]);
 }
 
+static void
+restrict_process(const char *user, const char *group)
+{
+	struct group *gr = NULL;
+	struct passwd *pw = NULL;
+	errno = 0;
+
+	if (group != NULL) {
+		if (initgroups(user, gr->gr_gid) == -1)
+			errx(1, "User not in group list");
+		if ((gr = getgrnam(group)) == NULL)
+			errx(1, "Group %s does not exist", group);
+		if (setgid(gr->gr_gid) == -1)
+			err(1, "%s", group);
+	}
+
+	if (user != NULL) {
+		if ((pw = getpwnam(user)) == NULL)
+			errx(1, "User %s does not exist", user);
+		if (setuid(pw->pw_uid) == -1)
+			err(1, "%s", user);
+	}
+}
+
 static void
 usage(void)
 {
 	(void)fprintf(stderr,
-	    "usage: daemon [-cf] [-p pidfile] command arguments ...\n");
+	    "usage: daemon [-cf] [-g group] [-p pidfile] [-u user] command "
+		"arguments ...\n");
 	exit(1);
 }