o Add -u <username> flag to jail(8): set user context before exec.

PR:		bin/44320
Submitted by:	Mike Matsnev <mike@po.cs.msu.su>
Reviewed by:	-current
MFC after:	6 weeks

usr.sbin/jail/Makefile

@@ -2,6 +2,8 @@
 
 PROG=	jail
 MAN=	jail.8
+DPADD=	${LIBUTIL}
+LDADD=	-lutil
 
 WARNS?=	2
 

usr.sbin/jail/jail.8

@@ -41,12 +41,29 @@
 .Nd "imprison process and its descendants"
 .Sh SYNOPSIS
 .Nm
+.Op Fl u Ar username
 .Ar path hostname ip-number command ...
 .Sh DESCRIPTION
 The
 .Nm
 utility imprisons a process and all future descendants.
 .Pp
+The options are as follows:
+.Bl -tag -width ".Fl u Ar username"
+.It Fl u Ar username
+The user name as whom the
+.Ar command
+should run.
+.It Ar path
+Directory which is to be the root of the prison.
+.It Ar hostname
+Hostname of the prison.
+.It Ar ip-number
+IP number assigned to the prison.
+.It Ar command
+Pathname of the program which is to be executed.
+.El
+.Pp
 Please see the
 .Xr jail 2
 man page for further details.

usr.sbin/jail/jail.c

@@ -10,44 +10,97 @@
  * 
  */
 
-#include <sys/types.h>
+#include <sys/param.h>
 #include <sys/jail.h>
 
 #include <netinet/in.h>
 #include <arpa/inet.h>
 
 #include <err.h>
+#include <grp.h>
+#include <login_cap.h>
+#include <pwd.h>
 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>
 #include <unistd.h>
 
+static void	usage(void);
+
 int
 main(int argc, char **argv)
 {
+	login_cap_t *lcap;
 	struct jail j;
-	int i;
+	struct passwd *pwd;
 	struct in_addr in;
+	int ch, groups[NGROUPS], i, ngroups;
+	char *username;
 
-	if (argc < 5) 
-		errx(1, "usage: %s path hostname ip-number command ...\n",
-		    argv[0]);
-	i = chdir(argv[1]);
+	username = NULL;
+
+	while ((ch = getopt(argc, argv, "u:")) != -1)
+		switch (ch) {
+		case 'u':
+			username = optarg;
+			break;
+		default:
+			usage();
+			break;
+		}
+	argc -= optind;
+	argv += optind;
+	if (argc < 4)
+		usage();
+
+	if (username != NULL) {
+		pwd = getpwnam(username);
+		if (pwd == NULL)
+			err(1, "getpwnam %s", username);
+		lcap = login_getpwclass(pwd);
+		if (lcap == NULL)
+			err(1, "getpwclass failed", username);
+		ngroups = NGROUPS;
+		i = getgrouplist(username, pwd->pw_gid, groups, &ngroups);
+		if (i)
+			err(1, "getgrouplist %s", username);
+	}
+	i = chdir(argv[0]);
 	if (i)
-		err(1, "chdir %s", argv[1]);
+		err(1, "chdir %s", argv[0]);
 	memset(&j, 0, sizeof(j));
 	j.version = 0;
-	j.path = argv[1];
-	j.hostname = argv[2];
-	i = inet_aton(argv[3], &in);
+	j.path = argv[0];
+	j.hostname = argv[1];
+	i = inet_aton(argv[2], &in);
 	if (!i)
 		errx(1, "Couldn't make sense of ip-number\n");
 	j.ip_number = ntohl(in.s_addr);
 	i = jail(&j);
 	if (i)
 		err(1, "Imprisonment failed");
-	i = execv(argv[4], argv + 4);
+	if (username != NULL) {
+		i = setgroups(ngroups, groups);
+		if (i)
+			err(1, "setgroups failed");
+		i = setgid(pwd->pw_gid);
+		if (i)
+			err(1, "setgid failed");
+		i = setusercontext(lcap, pwd, pwd->pw_uid,
+		    LOGIN_SETALL & ~LOGIN_SETGROUP);
+		if (i)
+			err(1, "setusercontext failed");
+	}
+	i = execv(argv[3], argv + 3);
 	if (i)
-		err(1, "execv(%s)", argv[4]);
+		err(1, "execv(%s)", argv[3]);
 	exit (0);
 }
+
+static void
+usage(void)
+{
+
+	errx(1,
+	    "Usage: jail [-u username] path hostname ip-number command ...");
+}