@@ -17,6 +17,7 @@ TARGETS += drivers/net/bonding
 TARGETS += drivers/net/team
 TARGETS += efivarfs
 TARGETS += exec
+TARGETS += fchmodat4
 TARGETS += filesystems
 TARGETS += filesystems/binderfs
 TARGETS += filesystems/epoll

@@ -0,0 +1,2 @@
+# SPDX-License-Identifier: GPL-2.0-only
+/*_test

@@ -0,0 +1,6 @@
+# SPDX-License-Identifier: GPL-2.0-or-later
+
+CFLAGS += -Wall -O2 -g -fsanitize=address -fsanitize=undefined
+TEST_GEN_PROGS := fchmodat4_test
+
+include ../lib.mk

@@ -0,0 +1,151 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+
+#define _GNU_SOURCE
+#include <fcntl.h>
+#include <sys/stat.h>
+#include <sys/types.h>
+#include <syscall.h>
+#include <unistd.h>
+
+#include "../kselftest.h"
+
+#ifndef __NR_fchmodat4
+	#if defined __alpha__
+		#define __NR_fchmodat4 561
+	#elif defined _MIPS_SIM
+		#if _MIPS_SIM == _MIPS_SIM_ABI32	/* o32 */
+			#define __NR_fchmodat4 (451 + 4000)
+		#endif
+		#if _MIPS_SIM == _MIPS_SIM_NABI32	/* n32 */
+			#define __NR_fchmodat4 (451 + 6000)
+		#endif
+		#if _MIPS_SIM == _MIPS_SIM_ABI64	/* n64 */
+			#define __NR_fchmodat4 (451 + 5000)
+		#endif
+	#elif defined __ia64__
+		#define __NR_fchmodat4 (451 + 1024)
+	#else
+		#define __NR_fchmodat4 451
+	#endif
+#endif
+
+int sys_fchmodat4(int dfd, const char *filename, mode_t mode, int flags)
+{
+	int ret = syscall(__NR_fchmodat4, dfd, filename, mode, flags);
+	return ret >= 0 ? ret : -errno;
+}
+
+int setup_testdir(void)
+{
+	int dfd, ret;
+	char dirname[] = "/tmp/ksft-fchmodat4.XXXXXX";
+
+	/* Make the top-level directory. */
+	if (!mkdtemp(dirname))
+		ksft_exit_fail_msg("setup_testdir: failed to create tmpdir\n");
+
+	dfd = open(dirname, O_PATH | O_DIRECTORY);
+	if (dfd < 0)
+		ksft_exit_fail_msg("setup_testdir: failed to open tmpdir\n");
+
+	ret = openat(dfd, "regfile", O_CREAT | O_WRONLY | O_TRUNC, 0644);
+	if (ret < 0)
+		ksft_exit_fail_msg("setup_testdir: failed to create file in tmpdir\n");
+	close(ret);
+
+	ret = symlinkat("regfile", dfd, "symlink");
+	if (ret < 0)
+		ksft_exit_fail_msg("setup_testdir: failed to create symlink in tmpdir\n");
+
+	return dfd;
+}
+
+int expect_mode(int dfd, const char *filename, mode_t expect_mode)
+{
+	struct stat st;
+	int ret = fstatat(dfd, filename, &st, AT_SYMLINK_NOFOLLOW);
+
+	if (ret)
+		ksft_exit_fail_msg("expect_mode: %s: fstatat failed\n", filename);
+
+	return (st.st_mode == expect_mode);
+}
+
+void test_regfile(void)
+{
+	int dfd, ret;
+
+	dfd = setup_testdir();
+
+	ret = sys_fchmodat4(dfd, "regfile", 0640, 0);
+
+	if (ret < 0)
+		ksft_exit_fail_msg("test_regfile: fchmodat4(noflag) failed\n");
+
+	if (!expect_mode(dfd, "regfile", 0100640))
+		ksft_exit_fail_msg("test_regfile: wrong file mode bits after fchmodat4\n");
+
+	ret = sys_fchmodat4(dfd, "regfile", 0600, AT_SYMLINK_NOFOLLOW);
+
+	if (ret < 0)
+		ksft_exit_fail_msg("test_regfile: fchmodat4(AT_SYMLINK_NOFOLLOW) failed\n");
+
+	if (!expect_mode(dfd, "regfile", 0100600))
+		ksft_exit_fail_msg("test_regfile: wrong file mode bits after fchmodat4 with nofollow\n");
+
+	ksft_test_result_pass("fchmodat4(regfile)\n");
+}
+
+void test_symlink(void)
+{
+	int dfd, ret;
+
+	dfd = setup_testdir();
+
+	ret = sys_fchmodat4(dfd, "symlink", 0640, 0);
+
+	if (ret < 0)
+		ksft_exit_fail_msg("test_symlink: fchmodat4(noflag) failed\n");
+
+	if (!expect_mode(dfd, "regfile", 0100640))
+		ksft_exit_fail_msg("test_symlink: wrong file mode bits after fchmodat4\n");
+
+	if (!expect_mode(dfd, "symlink", 0120777))
+		ksft_exit_fail_msg("test_symlink: wrong symlink mode bits after fchmodat4\n");
+
+	ret = sys_fchmodat4(dfd, "symlink", 0600, AT_SYMLINK_NOFOLLOW);
+
+	/*
+	 * On certain filesystems (xfs or btrfs), chmod operation fails. So we
+	 * first check the symlink target but if the operation fails we mark the
+	 * test as skipped.
+	 *
+	 * https://sourceware.org/legacy-ml/libc-alpha/2020-02/msg00467.html
+	 */
+	if (ret == 0 && !expect_mode(dfd, "symlink", 0120600))
+		ksft_exit_fail_msg("test_symlink: wrong symlink mode bits after fchmodat4 with nofollow\n");
+
+	if (!expect_mode(dfd, "regfile", 0100640))
+		ksft_exit_fail_msg("test_symlink: wrong file mode bits after fchmodat4 with nofollow\n");
+
+	if (ret != 0)
+		ksft_test_result_skip("fchmodat4(symlink)\n");
+	else
+		ksft_test_result_pass("fchmodat4(symlink)\n");
+}
+
+#define NUM_TESTS 2
+
+int main(int argc, char **argv)
+{
+	ksft_print_header();
+	ksft_set_plan(NUM_TESTS);
+
+	test_regfile();
+	test_symlink();
+
+	if (ksft_get_fail_cnt() + ksft_get_error_cnt() > 0)
+		ksft_exit_fail();
+	else
+		ksft_exit_pass();
+}