o Add -l option to jail(8) similar to su(1): before running jail'ed

program under specific user's credentials, clean the environment and
set only a few variables.

PR:		bin/70024
Submitted by:	demon
MFC after:	1 month

2 files changed, 50 insertions, 6 deletions

diff --git a/usr.sbin/jail/jail.8 b/usr.sbin/jail/jail.8
index a3b20d5..51eb5f6 100644
--- a/usr.sbin/jail/jail.8
+++ b/usr.sbin/jail/jail.8
@@ -42,7 +42,7 @@
 .Sh SYNOPSIS
 .Nm
 .Op Fl i
-.Op Fl u Ar username | Fl U Ar username
+.Op Fl l Fl u Ar username | Fl U Ar username
 .Ar path hostname ip-number command ...
 .Sh DESCRIPTION
 The
@@ -53,6 +53,24 @@ The options are as follows:
 .Bl -tag -width ".Fl u Ar username"
 .It Fl i
 Output the jail identifier of the newly created jail.
+.It Fl l
+Run program in the clean environment.
+The environment is discarded except for
+.Ev HOME ,
+.Ev SHELL ,
+.Ev TERM
+and
+.Ev USER .
+.Ev HOME
+and
+.Ev SHELL
+are set to the target login's default values.
+.Ev USER
+is set to the target login.
+.Ev TERM
+is imported from your current environment.
+The environment variables from the login class capability database for the
+target login are also set.
 .It Fl u Ar username
 The user name from host environment as whom the
 .Ar command
diff --git a/usr.sbin/jail/jail.c b/usr.sbin/jail/jail.c
index ab188ee..0f379a7 100644
--- a/usr.sbin/jail/jail.c
+++ b/usr.sbin/jail/jail.c
@@ -20,6 +20,7 @@ __FBSDID("$FreeBSD$");
 #include <errno.h>
 #include <grp.h>
 #include <login_cap.h>
+#include <paths.h>
 #include <pwd.h>
 #include <stdio.h>
 #include <stdlib.h>
@@ -27,6 +28,7 @@ __FBSDID("$FreeBSD$");
 #include <unistd.h>
 
 static void	usage(void);
+extern char	**environ;
 
 #define GET_USER_INFO do {						\
 	pwd = getpwnam(username);					\
@@ -51,13 +53,15 @@ main(int argc, char **argv)
 	struct jail j;
 	struct passwd *pwd;
 	struct in_addr in;
-	int ch, groups[NGROUPS], i, iflag, ngroups, uflag, Uflag;
+	int ch, groups[NGROUPS], i, iflag, lflag, ngroups, uflag, Uflag;
 	char path[PATH_MAX], *username;
+	static char *cleanenv;
+	const char *shell, *p;
 
-	iflag = uflag = Uflag = 0;
-	username = NULL;
+	iflag = lflag = uflag = Uflag = 0;
+	username = cleanenv = NULL;
 
-	while ((ch = getopt(argc, argv, "iu:U:")) != -1) {
+	while ((ch = getopt(argc, argv, "ilu:U:")) != -1) {
 		switch (ch) {
 		case 'i':
 			iflag = 1;
@@ -70,6 +74,9 @@ main(int argc, char **argv)
 			username = optarg;
 			Uflag = 1;
 			break;
+		case 'l':
+			lflag = 1;
+			break;
 		default:
 			usage();
 		}
@@ -80,6 +87,8 @@ main(int argc, char **argv)
 		usage();
 	if (uflag && Uflag)
 		usage();
+	if (lflag && username == NULL)
+		usage();
 	if (uflag)
 		GET_USER_INFO;
 	if (realpath(argv[0], path) == NULL)
@@ -103,6 +112,10 @@ main(int argc, char **argv)
 	if (username != NULL) {
 		if (Uflag)
 			GET_USER_INFO;
+		if (lflag) {
+			p = getenv("TERM");
+			environ = &cleanenv;
+		}
 		if (setgroups(ngroups, groups) != 0)
 			err(1, "setgroups");
 		if (setgid(pwd->pw_gid) != 0)
@@ -112,6 +125,19 @@ main(int argc, char **argv)
 			err(1, "setusercontext");
 		login_close(lcap);
 	}
+	if (lflag) {
+		if (*pwd->pw_shell)
+			shell = pwd->pw_shell;
+		else
+			shell = _PATH_BSHELL;
+		if (chdir(pwd->pw_dir) < 0)
+			errx(1, "no home directory");
+		setenv("HOME", pwd->pw_dir, 1);
+		setenv("SHELL", shell, 1);
+		setenv("USER", pwd->pw_name, 1);
+		if (p)
+			setenv("TERM", p, 1);
+	}
 	if (execv(argv[3], argv + 3) != 0)
 		err(1, "execv: %s", argv[3]);
 	exit(0);
@@ -122,7 +148,7 @@ usage(void)
 {
 
 	(void)fprintf(stderr, "%s%s\n",
-	     "usage: jail [-i] [-u username | -U username]",
+	     "usage: jail [-i] [-l -u username | -U username]",
 	     " path hostname ip-number command ...");
 	exit(1);
 }