1 files changed, 133 insertions, 0 deletions
diff --git a/tests/sys/kern/jail_lookup_root.c b/tests/sys/kern/jail_lookup_root.c
new file mode 100644
index 000000000000..34e89f4aea2b
--- /dev/null
+++ b/tests/sys/kern/jail_lookup_root.c
@@ -0,0 +1,133 @@
+/*-
+ * SPDX-License-Identifier: BSD-2-Clause
+ *
+ * Copyright (c) 2025 Mark Johnston <markj@FreeBSD.org>
+ */
+
+#include <sys/param.h>
+#include <sys/jail.h>
+#include <sys/mount.h>
+#include <sys/stat.h>
+
+#include <err.h>
+#include <errno.h>
+#include <fcntl.h>
+#include <jail.h>
+#include <mntopts.h>
+#include <stdio.h>
+#include <stdlib.h>
+
+#include <atf-c.h>
+
+static void
+mkdir_checked(const char *dir, mode_t mode)
+{
+	int error;
+
+	error = mkdir(dir, mode);
+	ATF_REQUIRE_MSG(error == 0 || errno == EEXIST,
+	    "mkdir %s: %s", dir, strerror(errno));
+}
+
+static void __unused
+mount_nullfs(const char *dir, const char *target)
+{
+	struct iovec *iov;
+	char errmsg[1024];
+	int error, iovlen;
+
+	iov = NULL;
+	iovlen = 0;
+
+	build_iovec(&iov, &iovlen, __DECONST(char *, "fstype"),
+	    __DECONST(char *, "nullfs"), (size_t)-1);
+	build_iovec(&iov, &iovlen, __DECONST(char *, "fspath"),
+	    __DECONST(char *, target), (size_t)-1);
+	build_iovec(&iov, &iovlen, __DECONST(char *, "from"),
+	    __DECONST(char *, dir), (size_t)-1);
+	build_iovec(&iov, &iovlen, __DECONST(char *, "errmsg"),
+	    errmsg, sizeof(errmsg));
+
+	errmsg[0] = '\0';
+	error = nmount(iov, iovlen, 0);
+	ATF_REQUIRE_MSG(error == 0, "nmount: %s",
+	    errmsg[0] != '\0' ? errmsg : strerror(errno));
+
+	free_iovec(&iov, &iovlen);
+}
+
+ATF_TC_WITH_CLEANUP(jail_root);
+ATF_TC_HEAD(jail_root, tc)
+{
+	atf_tc_set_md_var(tc, "require.user", "root");
+}
+ATF_TC_BODY(jail_root, tc)
+{
+	int error, fd, jid;
+
+	mkdir_checked("./root", 0755);
+	mkdir_checked("./root/a", 0755);
+	mkdir_checked("./root/b", 0755);
+	mkdir_checked("./root/a/c", 0755);
+
+	jid = jail_setv(JAIL_CREATE | JAIL_ATTACH,
+	    "name", "nullfs_jail_root_test",
+	    "allow.mount", "true",
+	    "allow.mount.nullfs", "true",
+	    "enforce_statfs", "1",
+	    "path", "./root",
+	    "persist", NULL,
+	    NULL);
+	ATF_REQUIRE_MSG(jid >= 0, "jail_setv: %s", jail_errmsg);
+
+	mount_nullfs("/a", "/b");
+
+	error = chdir("/b/c");
+	ATF_REQUIRE(error == 0);
+
+	error = rename("/a/c", "/c");
+	ATF_REQUIRE(error == 0);
+
+	/* Descending to the jail root should be ok. */
+	error = chdir("..");
+	ATF_REQUIRE(error == 0);
+
+	/* Going beyond the root will trigger an error. */
+	error = chdir("..");
+	ATF_REQUIRE_ERRNO(ENOENT, error != 0);
+	fd = open("..", O_RDONLY | O_DIRECTORY);
+	ATF_REQUIRE_ERRNO(ENOENT, fd < 0);
+}
+ATF_TC_CLEANUP(jail_root, tc)
+{
+	struct statfs fs;
+	fsid_t fsid;
+	int error, jid;
+
+	error = statfs("./root/b", &fs);
+	if (error != 0)
+		err(1, "statfs ./b");
+	fsid = fs.f_fsid;
+	error = statfs("./root", &fs);
+	if (error != 0)
+		err(1, "statfs ./root");
+	if (fsid.val[0] != fs.f_fsid.val[0] ||
+	    fsid.val[1] != fs.f_fsid.val[1]) {
+		error = unmount("./root/b", 0);
+		if (error != 0)
+			err(1, "unmount ./root/b");
+	}
+
+	jid = jail_getid("nullfs_jail_root_test");
+	if (jid >= 0) {
+		error = jail_remove(jid);
+		if (error != 0)
+			err(1, "jail_remove");
+	}
+}
+
+ATF_TP_ADD_TCS(tp)
+{
+	ATF_TP_ADD_TC(tp, jail_root);
+	return (atf_no_error());
+}