selftests/filesystems: add chown() test for anonymous inodes

Test that anonymous inodes cannot be chown()ed.

Link: https://lore.kernel.org/20250407-work-anon_inode-v1-6-53a44c20d44e@kernel.org
Reviewed-by: Jeff Layton <jlayton@kernel.org>
Signed-off-by: Christian Brauner <brauner@kernel.org>

Author: brauner

tools/testing/selftests/filesystems/.gitignore

@@ -2,3 +2,4 @@
 dnotify_test
 devpts_pts
 file_stressor
+anon_inode_test

tools/testing/selftests/filesystems/Makefile

@@ -1,7 +1,7 @@
 # SPDX-License-Identifier: GPL-2.0
 
 CFLAGS += $(KHDR_INCLUDES)
-TEST_GEN_PROGS := devpts_pts file_stressor
+TEST_GEN_PROGS := devpts_pts file_stressor anon_inode_test
 TEST_GEN_PROGS_EXTENDED := dnotify_test
 
 include ../lib.mk

tools/testing/selftests/filesystems/anon_inode_test.c

@@ -0,0 +1,26 @@
+// SPDX-License-Identifier: GPL-2.0
+#define _GNU_SOURCE
+#define __SANE_USERSPACE_TYPES__
+
+#include <fcntl.h>
+#include <stdio.h>
+#include <sys/stat.h>
+
+#include "../kselftest_harness.h"
+#include "overlayfs/wrappers.h"
+
+TEST(anon_inode_no_chown)
+{
+	int fd_context;
+
+	fd_context = sys_fsopen("tmpfs", 0);
+	ASSERT_GE(fd_context, 0);
+
+	ASSERT_LT(fchown(fd_context, 1234, 5678), 0);
+	ASSERT_EQ(errno, EOPNOTSUPP);
+
+	EXPECT_EQ(close(fd_context), 0);
+}
+
+TEST_HARNESS_MAIN
+