jail: add jexec -d, to specify a working directory

PR:		283170
Submitted by:	DtxdF at disroot.org

usr.sbin/jexec/jexec.8

@@ -23,7 +23,7 @@
 .\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 .\" SUCH DAMAGE.
 .\"
-.Dd August 12, 2024
+.Dd March 5, 2025
 .Dt JEXEC 8
 .Os
 .Sh NAME
@@ -32,6 +32,7 @@
 .Sh SYNOPSIS
 .Nm
 .Op Fl l
+.Op Fl d Ar working-directory
 .Op Fl u Ar username | Fl U Ar username
 .Ar jail Op Ar command ...
 .Sh DESCRIPTION
@@ -48,6 +49,9 @@ is not specified then the user's shell is used.
 .Pp
 The following options are available:
 .Bl -tag -width indent
+.It Fl d Ar working-directory
+The working directory for running commands inside the jail.
+The default is the jail root directory.
 .It Fl l
 Execute in a clean environment.
 The environment is discarded except for
@@ -59,7 +63,9 @@ If a user is specified (via
 .Fl u
 or
 .Fl U ) ,
-commands are run from that (possibly jailed) user's directory.
+and absent the
+.Fl d
+option, commands are run from that (possibly jailed) user's directory.
 .It Fl u Ar username
 The user name from host environment as whom the
 .Ar command

usr.sbin/jexec/jexec.c

@@ -58,16 +58,22 @@ main(int argc, char *argv[])
 {
 	int jid;
 	login_cap_t *lcap = NULL;
-	int ch, clean, uflag, Uflag;
+	int ch, clean, dflag, uflag, Uflag;
 	char *cleanenv;
 	const struct passwd *pwd = NULL;
 	const char *username, *shell, *term;
+	const char *workdir;
 
-	ch = clean = uflag = Uflag = 0;
+	ch = clean = dflag = uflag = Uflag = 0;
 	username = NULL;
+	workdir = "/";
 
-	while ((ch = getopt(argc, argv, "lnu:U:")) != -1) {
+	while ((ch = getopt(argc, argv, "d:lnu:U:")) != -1) {
 		switch (ch) {
+		case 'd':
+			workdir = optarg;
+			dflag = 1;
+			break;
 		case 'l':
 			clean = 1;
 			break;
@@ -102,8 +108,8 @@ main(int argc, char *argv[])
 		errx(1, "%s", jail_errmsg);
 	if (jail_attach(jid) == -1)
 		err(1, "jail_attach(%d)", jid);
-	if (chdir("/") == -1)
-		err(1, "chdir(): /");
+	if (chdir(workdir) == -1)
+		err(1, "chdir(): %s", workdir);
 
 	/* Set up user environment */
 	if (clean || username != NULL) {
@@ -129,7 +135,7 @@ main(int argc, char *argv[])
 		setenv("HOME", pwd->pw_dir, 1);
 		setenv("SHELL",
 		    *pwd->pw_shell ? pwd->pw_shell : _PATH_BSHELL, 1);
-		if (clean && username && chdir(pwd->pw_dir) < 0)
+		if (clean && username && !dflag && chdir(pwd->pw_dir) < 0)
 			err(1, "chdir: %s", pwd->pw_dir);
 		endpwent();
 	}
@@ -186,6 +192,7 @@ usage(void)
 {
 
 	fprintf(stderr, "%s\n",
-	    "usage: jexec [-l] [-u username | -U username] jail [command ...]");
+	    "usage: jexec [-l] [-d working-directory] [-u username | -U username] jail\n"
+	    "       [command ...]");
 	exit(1);
 }