Linux kernel mirror (for testing)
git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
kernel
os
linux
selftests/landlock: Add filesystem access benchmark
fs_bench benchmarks the performance of Landlock's path walk
by exercising it in a scenario that amplifies Landlock's overhead:
* Create a large number of nested directories
* Enforce a Landlock policy in which a rule is associated with each of
these subdirectories
* Benchmark openat() applied to the deepest directory,
forcing Landlock to walk the entire path.
Signed-off-by: Günther Noack <gnoack3000@gmail.com>
Link: https://lore.kernel.org/r/20260206151154.97915-3-gnoack3000@gmail.com
[mic: Fix missing mode with O_CREAT, improve text consistency, sort
includes]
Signed-off-by: Mickaël Salaün <mic@digikod.net>
authored by
Günther Noack
and committed by
Mickaël Salaün
9adbe893
de4b09ab
+216
+1
tools/testing/selftests/landlock/.gitignore
+1
tools/testing/selftests/landlock/.gitignore
+1
tools/testing/selftests/landlock/Makefile
+1
tools/testing/selftests/landlock/Makefile
+214
tools/testing/selftests/landlock/fs_bench.c
+214
tools/testing/selftests/landlock/fs_bench.c
···
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// SPDX-License-Identifier: GPL-2.0
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/*
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* Landlock filesystem benchmark
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*
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* This program benchmarks the time required for file access checks. We use a
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* large number (-d flag) of nested directories where each directory inode has
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* an associated Landlock rule, and we repeatedly (-n flag) exercise a file
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* access for which Landlock has to walk the path all the way up to the root.
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*
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* With an increasing number of nested subdirectories, Landlock's portion of the
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* overall system call time increases, which makes the effects of Landlock
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* refactorings more measurable.
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*
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* This benchmark does *not* measure the building of the Landlock ruleset. The
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* time required to add all these rules is not large enough to be easily
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* measurable. A separate benchmark tool would be better to test that, and that
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* tool could then also use a simpler file system layout.
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*
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* Copyright © 2026 Google LLC
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*/
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#define _GNU_SOURCE
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#include <err.h>
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#include <errno.h>
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#include <fcntl.h>
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#include <linux/landlock.h>
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#include <linux/prctl.h>
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#include <stdbool.h>
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#include <stdio.h>
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#include <stdlib.h>
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#include <string.h>
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#include <sys/prctl.h>
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#include <sys/stat.h>
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#include <sys/times.h>
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#include <time.h>
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#include <unistd.h>
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#include "wrappers.h"
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static void usage(const char *const argv0)
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{
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printf("Usage:\n");
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printf(" %s [OPTIONS]\n", argv0);
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printf("\n");
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printf(" Benchmark expensive Landlock checks for D nested dirs\n");
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printf("\n");
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printf("Options:\n");
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printf(" -h help\n");
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printf(" -L disable Landlock (as a baseline)\n");
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printf(" -d D set directory depth to D\n");
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printf(" -n N set number of benchmark iterations to N\n");
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}
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/*
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* Build a deep directory, enforce Landlock and return the FD to the
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* deepest dir. On any failure, exit the process with an error.
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*/
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static int build_directory(size_t depth, const bool use_landlock)
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{
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const char *path = "d"; /* directory name */
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int abi, ruleset_fd, curr, prev;
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if (use_landlock) {
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abi = landlock_create_ruleset(NULL, 0,
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LANDLOCK_CREATE_RULESET_VERSION);
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if (abi < 7)
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err(1, "Landlock ABI too low: got %d, wanted 7+", abi);
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}
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ruleset_fd = -1;
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if (use_landlock) {
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struct landlock_ruleset_attr attr = {
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.handled_access_fs = LANDLOCK_ACCESS_FS_IOCTL_DEV |
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LANDLOCK_ACCESS_FS_WRITE_FILE |
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LANDLOCK_ACCESS_FS_MAKE_REG,
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};
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ruleset_fd = landlock_create_ruleset(&attr, sizeof(attr), 0U);
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if (ruleset_fd < 0)
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err(1, "landlock_create_ruleset");
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}
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curr = open(".", O_PATH);
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if (curr < 0)
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err(1, "open(.)");
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while (depth--) {
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if (use_landlock) {
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struct landlock_path_beneath_attr attr = {
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.allowed_access = LANDLOCK_ACCESS_FS_IOCTL_DEV,
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.parent_fd = curr,
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};
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if (landlock_add_rule(ruleset_fd,
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LANDLOCK_RULE_PATH_BENEATH, &attr,
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0) < 0)
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err(1, "landlock_add_rule");
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}
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if (mkdirat(curr, path, 0700) < 0)
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err(1, "mkdirat(%s)", path);
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prev = curr;
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curr = openat(curr, path, O_PATH);
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if (curr < 0)
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err(1, "openat(%s)", path);
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close(prev);
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}
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if (use_landlock) {
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if (prctl(PR_SET_NO_NEW_PRIVS, 1, 0, 0, 0) < 0)
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err(1, "prctl");
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if (landlock_restrict_self(ruleset_fd, 0) < 0)
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err(1, "landlock_restrict_self");
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}
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close(ruleset_fd);
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return curr;
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}
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static void remove_recursively(const size_t depth)
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{
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const char *path = "d"; /* directory name */
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int fd = openat(AT_FDCWD, ".", O_PATH);
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if (fd < 0)
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err(1, "openat(.)");
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for (size_t i = 0; i < depth - 1; i++) {
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int oldfd = fd;
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fd = openat(fd, path, O_PATH);
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if (fd < 0)
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err(1, "openat(%s)", path);
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close(oldfd);
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}
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for (size_t i = 0; i < depth; i++) {
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if (unlinkat(fd, path, AT_REMOVEDIR) < 0)
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err(1, "unlinkat(%s)", path);
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int newfd = openat(fd, "..", O_PATH);
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close(fd);
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fd = newfd;
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}
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close(fd);
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}
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int main(int argc, char *argv[])
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{
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bool use_landlock = true;
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size_t num_iterations = 100000;
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size_t num_subdirs = 10000;
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int c, curr, fd;
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struct tms start_time, end_time;
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setbuf(stdout, NULL);
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while ((c = getopt(argc, argv, "hLd:n:")) != -1) {
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switch (c) {
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case 'h':
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usage(argv[0]);
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return EXIT_SUCCESS;
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case 'L':
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use_landlock = false;
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break;
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case 'd':
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num_subdirs = atoi(optarg);
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break;
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case 'n':
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num_iterations = atoi(optarg);
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break;
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default:
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usage(argv[0]);
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return EXIT_FAILURE;
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}
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}
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printf("*** Benchmark ***\n");
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printf("%zu dirs, %zu iterations, %s Landlock\n", num_subdirs,
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num_iterations, use_landlock ? "with" : "without");
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if (times(&start_time) == -1)
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err(1, "times");
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curr = build_directory(num_subdirs, use_landlock);
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for (int i = 0; i < num_iterations; i++) {
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fd = openat(curr, "file.txt", O_CREAT | O_TRUNC | O_WRONLY,
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0600);
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if (use_landlock) {
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if (fd == 0)
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errx(1, "openat succeeded, expected EACCES");
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if (errno != EACCES)
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err(1, "openat expected EACCES, but got");
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}
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if (fd != -1)
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close(fd);
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}
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if (times(&end_time) == -1)
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err(1, "times");
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printf("*** Benchmark concluded ***\n");
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printf("System: %ld clocks\n",
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end_time.tms_stime - start_time.tms_stime);
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printf("User : %ld clocks\n",
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end_time.tms_utime - start_time.tms_utime);
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printf("Clocks per second: %ld\n", CLOCKS_PER_SEC);
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close(curr);
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remove_recursively(num_subdirs);
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}