[LTP] [PATCH STAGING 04/16] fchroot01: test fchroot() with a directory fd

[Andrea Cervesato]

From: Andrea Cervesato <andrea.cervesato@suse.com>

Verify that fchroot() with a directory fd moves the process root to
the directory referenced by the fd.

fchroot() was introduced in Linux v7.3, so the test is added to the
staging runtest file.

Signed-off-by: Andrea Cervesato <andrea.cervesato@suse.com>
---
 runtest/staging                               |  2 +
 testcases/kernel/syscalls/fchroot/.gitignore  |  1 +
 testcases/kernel/syscalls/fchroot/Makefile    |  7 ++++
 testcases/kernel/syscalls/fchroot/fchroot01.c | 57 +++++++++++++++++++++++++++
 4 files changed, 67 insertions(+)

diff --git a/runtest/staging b/runtest/staging
index ef1cdea15..733d5609a 100644
--- a/runtest/staging
+++ b/runtest/staging
@@ -1 +1,3 @@
 # Tests for features that are not yet in the stable kernel ABI
+
+fchroot01 fchroot01
diff --git a/testcases/kernel/syscalls/fchroot/.gitignore b/testcases/kernel/syscalls/fchroot/.gitignore
new file mode 100644
index 000000000..03ebdbe7a
--- /dev/null
+++ b/testcases/kernel/syscalls/fchroot/.gitignore
@@ -0,0 +1 @@
+fchroot01
diff --git a/testcases/kernel/syscalls/fchroot/Makefile b/testcases/kernel/syscalls/fchroot/Makefile
new file mode 100644
index 000000000..137550149
--- /dev/null
+++ b/testcases/kernel/syscalls/fchroot/Makefile
@@ -0,0 +1,7 @@
+# SPDX-License-Identifier: GPL-2.0-or-later
+# Copyright (C) 2026 SUSE LLC Andrea Cervesato <andrea.cervesato@suse.com>
+
+top_srcdir		?= ../../../..
+
+include $(top_srcdir)/include/mk/testcases.mk
+include $(top_srcdir)/include/mk/generic_leaf_target.mk
diff --git a/testcases/kernel/syscalls/fchroot/fchroot01.c b/testcases/kernel/syscalls/fchroot/fchroot01.c
new file mode 100644
index 000000000..fb4894519
--- /dev/null
+++ b/testcases/kernel/syscalls/fchroot/fchroot01.c
@@ -0,0 +1,57 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ * Copyright (C) 2026 SUSE LLC Andrea Cervesato <andrea.cervesato@suse.com>
+ */
+
+/*\
+ * Test that :manpage:`fchroot(2)` with a regular directory fd moves the
+ * process root to the directory referenced by the fd.
+ *
+ * This is the fd-based counterpart of :manpage:`chroot(2)`, introduced in
+ * Linux v7.3. Root is required because fchroot() with a regular directory
+ * fd requires CAP_SYS_CHROOT.
+ *
+ * The syscall runs in a forked child so that the root of the parent
+ * process, which the test framework needs for its cleanup, is left
+ * untouched.
+ */
+
+#include <sys/stat.h>
+#include <fcntl.h>
+#include "tst_test.h"
+#include "lapi/fcntl.h"
+#include "lapi/syscalls.h"
+
+#define JAILDIR "jail"
+#define CANARY JAILDIR "/canary"
+
+static void run(void)
+{
+	struct stat st;
+
+	if (!SAFE_FORK()) {
+		int dfd = SAFE_OPEN(JAILDIR, O_PATH | O_DIRECTORY);
+
+		TST_EXP_PASS(tst_syscall(__NR_fchroot, dfd, 0),
+			"fchroot() with a directory fd");
+
+		TST_EXP_PASS(stat("/canary", &st),
+			"canary file visible under the new root");
+
+		exit(0);
+	}
+}
+
+static void setup(void)
+{
+	SAFE_MKDIR(JAILDIR, 0755);
+	SAFE_TOUCH(CANARY, 0644, NULL);
+}
+
+static struct tst_test test = {
+	.setup = setup,
+	.test_all = run,
+	.needs_root = 1,
+	.needs_tmpdir = 1,
+	.forks_child = 1,
+};

-- 
2.51.0