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selftests: Add fchmodat2 selftest
The test marks as skipped if a syscall with the AT_SYMLINK_NOFOLLOW flag fails. This is because not all filesystems support changing the mode bits of symlinks properly. These filesystems return an error but change the mode bits: newfstatat(4, "regfile", {st_mode=S_IFREG|0640, st_size=0, ...}, AT_SYMLINK_NOFOLLOW) = 0 newfstatat(4, "symlink", {st_mode=S_IFLNK|0777, st_size=7, ...}, AT_SYMLINK_NOFOLLOW) = 0 syscall_0x1c3(0x4, 0x55fa1f244396, 0x180, 0x100, 0x55fa1f24438e, 0x34) = -1 EOPNOTSUPP (Operation not supported) newfstatat(4, "regfile", {st_mode=S_IFREG|0640, st_size=0, ...}, AT_SYMLINK_NOFOLLOW) = 0 This happens with btrfs and xfs: $ tools/testing/selftests/fchmodat2/fchmodat2_test TAP version 13 1..1 ok 1 # SKIP fchmodat2(symlink) # Totals: pass:0 fail:0 xfail:0 xpass:0 skip:1 error:0 $ stat /tmp/ksft-fchmodat2.*/symlink File: /tmp/ksft-fchmodat2.3NCqlE/symlink -> regfile Size: 7 Blocks: 0 IO Block: 4096 symbolic link Device: 7,0 Inode: 133 Links: 1 Access: (0600/lrw-------) Uid: ( 0/ root) Gid: ( 0/ root) Signed-off-by: Alexey Gladkov <[email protected]> Message-Id: <4532a04a870ff589ba62ceeacf76f0bd81b9ba01.1689092120.git.legion@kernel.org> Signed-off-by: Christian Brauner <[email protected]>
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‎tools/testing/selftests/Makefile

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@@ -18,6 +18,7 @@ TARGETS += drivers/net/bonding
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TARGETS += drivers/net/team
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TARGETS += efivarfs
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TARGETS += exec
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TARGETS += fchmodat2
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TARGETS += filesystems
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TARGETS += filesystems/binderfs
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TARGETS += filesystems/epoll

‎tools/testing/selftests/fchmodat2/.gitignore

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# SPDX-License-Identifier: GPL-2.0-only
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/*_test

‎tools/testing/selftests/fchmodat2/Makefile

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# SPDX-License-Identifier: GPL-2.0-or-later
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CFLAGS += -Wall -O2 -g -fsanitize=address -fsanitize=undefined
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TEST_GEN_PROGS := fchmodat2_test
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include ../lib.mk

‎tools/testing/selftests/fchmodat2/fchmodat2_test.c

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// SPDX-License-Identifier: GPL-2.0-or-later
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#define _GNU_SOURCE
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#include <fcntl.h>
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#include <sys/stat.h>
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#include <sys/types.h>
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#include <syscall.h>
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#include <unistd.h>
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#include "../kselftest.h"
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#ifndef __NR_fchmodat2
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#if defined __alpha__
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#define __NR_fchmodat2 562
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#elif defined _MIPS_SIM
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#if _MIPS_SIM == _MIPS_SIM_ABI32 /* o32 */
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#define __NR_fchmodat2 (452 + 4000)
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#endif
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#if _MIPS_SIM == _MIPS_SIM_NABI32 /* n32 */
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#define __NR_fchmodat2 (452 + 6000)
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#endif
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#if _MIPS_SIM == _MIPS_SIM_ABI64 /* n64 */
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#define __NR_fchmodat2 (452 + 5000)
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#endif
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#elif defined __ia64__
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#define __NR_fchmodat2 (452 + 1024)
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#else
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#define __NR_fchmodat2 452
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#endif
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#endif
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int sys_fchmodat2(int dfd, const char *filename, mode_t mode, int flags)
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{
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int ret = syscall(__NR_fchmodat2, dfd, filename, mode, flags);
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return ret >= 0 ? ret : -errno;
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}
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int setup_testdir(void)
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{
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int dfd, ret;
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char dirname[] = "/tmp/ksft-fchmodat2.XXXXXX";
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/* Make the top-level directory. */
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if (!mkdtemp(dirname))
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ksft_exit_fail_msg("%s: failed to create tmpdir\n", __func__);
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dfd = open(dirname, O_PATH | O_DIRECTORY);
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if (dfd < 0)
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ksft_exit_fail_msg("%s: failed to open tmpdir\n", __func__);
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ret = openat(dfd, "regfile", O_CREAT | O_WRONLY | O_TRUNC, 0644);
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if (ret < 0)
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ksft_exit_fail_msg("%s: failed to create file in tmpdir\n",
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__func__);
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close(ret);
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ret = symlinkat("regfile", dfd, "symlink");
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if (ret < 0)
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ksft_exit_fail_msg("%s: failed to create symlink in tmpdir\n",
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__func__);
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return dfd;
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}
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int expect_mode(int dfd, const char *filename, mode_t expect_mode)
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{
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struct stat st;
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int ret = fstatat(dfd, filename, &st, AT_SYMLINK_NOFOLLOW);
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if (ret)
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ksft_exit_fail_msg("%s: %s: fstatat failed\n",
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__func__, filename);
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return (st.st_mode == expect_mode);
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}
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void test_regfile(void)
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{
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int dfd, ret;
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dfd = setup_testdir();
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ret = sys_fchmodat2(dfd, "regfile", 0640, 0);
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if (ret < 0)
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ksft_exit_fail_msg("%s: fchmodat2(noflag) failed\n", __func__);
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if (!expect_mode(dfd, "regfile", 0100640))
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ksft_exit_fail_msg("%s: wrong file mode bits after fchmodat2\n",
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__func__);
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ret = sys_fchmodat2(dfd, "regfile", 0600, AT_SYMLINK_NOFOLLOW);
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if (ret < 0)
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ksft_exit_fail_msg("%s: fchmodat2(AT_SYMLINK_NOFOLLOW) failed\n",
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__func__);
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if (!expect_mode(dfd, "regfile", 0100600))
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ksft_exit_fail_msg("%s: wrong file mode bits after fchmodat2 with nofollow\n",
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__func__);
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ksft_test_result_pass("fchmodat2(regfile)\n");
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}
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void test_symlink(void)
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{
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int dfd, ret;
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dfd = setup_testdir();
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ret = sys_fchmodat2(dfd, "symlink", 0640, 0);
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if (ret < 0)
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ksft_exit_fail_msg("%s: fchmodat2(noflag) failed\n", __func__);
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if (!expect_mode(dfd, "regfile", 0100640))
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ksft_exit_fail_msg("%s: wrong file mode bits after fchmodat2\n",
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__func__);
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if (!expect_mode(dfd, "symlink", 0120777))
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ksft_exit_fail_msg("%s: wrong symlink mode bits after fchmodat2\n",
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__func__);
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ret = sys_fchmodat2(dfd, "symlink", 0600, AT_SYMLINK_NOFOLLOW);
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/*
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* On certain filesystems (xfs or btrfs), chmod operation fails. So we
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* first check the symlink target but if the operation fails we mark the
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* test as skipped.
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*
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* https://sourceware.org/legacy-ml/libc-alpha/2020-02/msg00467.html
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*/
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if (ret == 0 && !expect_mode(dfd, "symlink", 0120600))
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ksft_exit_fail_msg("%s: wrong symlink mode bits after fchmodat2 with nofollow\n",
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__func__);
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if (!expect_mode(dfd, "regfile", 0100640))
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ksft_exit_fail_msg("%s: wrong file mode bits after fchmodat2 with nofollow\n",
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__func__);
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if (ret != 0)
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ksft_test_result_skip("fchmodat2(symlink)\n");
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else
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ksft_test_result_pass("fchmodat2(symlink)\n");
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}
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#define NUM_TESTS 2
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int main(int argc, char **argv)
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{
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ksft_print_header();
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ksft_set_plan(NUM_TESTS);
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test_regfile();
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test_symlink();
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if (ksft_get_fail_cnt() + ksft_get_error_cnt() > 0)
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ksft_exit_fail();
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else
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ksft_exit_pass();
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}

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