--chroot implementation thanks to Joerg Sonnenberger.

usr.bin/tar/bsdtar.c

@@ -137,6 +137,7 @@ static const char *tar_opts = "+Bb:C:cf:HhI:jkLlmnOoPprtT:UuvW:wX:xyZz";
 /* Fake short equivalents for long options that otherwise lack them. */
 enum {
 	OPTION_CHECK_LINKS=1,
+	OPTION_CHROOT,
 	OPTION_EXCLUDE,
 	OPTION_FAST_READ,
 	OPTION_FORMAT,
@@ -171,6 +172,7 @@ static const struct option tar_longopts[] = {
 	{ "bzip2",              no_argument,       NULL, 'j' },
 	{ "cd",                 required_argument, NULL, 'C' },
 	{ "check-links",        no_argument,       NULL, OPTION_CHECK_LINKS },
+	{ "chroot",             no_argument,       NULL, OPTION_CHROOT },
 	{ "compress",           no_argument,       NULL, 'Z' },
 	{ "confirmation",       no_argument,       NULL, 'w' },
 	{ "create",             no_argument,       NULL, 'c' },
@@ -322,6 +324,9 @@ main(int argc, char **argv)
 		case OPTION_CHECK_LINKS: /* GNU tar */
 			bsdtar->option_warn_links = 1;
 			break;
+		case OPTION_CHROOT: /* NetBSD */
+			bsdtar->option_chroot = 1;
+			break;
 		case OPTION_EXCLUDE: /* GNU tar */
 			if (exclude(bsdtar, optarg))
 				bsdtar_errc(bsdtar, 1, 0,

usr.bin/tar/bsdtar.h

@@ -57,6 +57,7 @@ struct bsdtar {
 	char		  create_compression; /* j, y, or z */
 	const char	 *compress_program;
 	char		  option_absolute_paths; /* -P */
+	char		  option_chroot; /* --chroot */
 	char		  option_dont_traverse_mounts; /* --one-file-system */
 	char		  option_fast_read; /* --fast-read */
 	char		  option_honor_nodump; /* --nodump */

usr.bin/tar/config_freebsd.h

@@ -38,6 +38,7 @@
 #undef	HAVE_ATTR_XATTR_H
 #define	HAVE_BZLIB_H 1
 #define	HAVE_CHFLAGS 1
+#define	HAVE_CHROOT 1
 #define	HAVE_DECL_OPTARG 1
 #define	HAVE_DECL_OPTIND 1
 #define	HAVE_DIRENT_D_NAMLEN 1

usr.bin/tar/read.c

@@ -118,6 +118,17 @@ read_archive(struct bsdtar *bsdtar, char mode)
 		    archive_error_string(a));
 
 	do_chdir(bsdtar);
+
+	if (mode == 'x' && bsdtar->option_chroot) {
+#if HAVE_CHROOT
+		if (chroot(".") != 0)
+			bsdtar_errc(bsdtar, 1, errno, "Can't chroot to \".\"");
+#else
+		bsdtar_errc(bsdtar, 1, 0,
+		    "chroot isn't supported on this platform");
+#endif
+	}
+
 	for (;;) {
 		/* Support --fast-read option */
 		if (bsdtar->option_fast_read &&