1 // SPDX-License-Identifier: GPL-2.0
2 /*
3 * Landlock filesystem benchmark
4 *
5 * This program benchmarks the time required for file access checks. We use a
6 * large number (-d flag) of nested directories where each directory inode has
7 * an associated Landlock rule, and we repeatedly (-n flag) exercise a file
8 * access for which Landlock has to walk the path all the way up to the root.
9 *
10 * With an increasing number of nested subdirectories, Landlock's portion of the
11 * overall system call time increases, which makes the effects of Landlock
12 * refactorings more measurable.
13 *
14 * This benchmark does *not* measure the building of the Landlock ruleset. The
15 * time required to add all these rules is not large enough to be easily
16 * measurable. A separate benchmark tool would be better to test that, and that
17 * tool could then also use a simpler file system layout.
18 *
19 * Copyright © 2026 Google LLC
20 */
21
22 #define _GNU_SOURCE
23 #include <err.h>
24 #include <errno.h>
25 #include <fcntl.h>
26 #include <linux/landlock.h>
27 #include <linux/prctl.h>
28 #include <stdbool.h>
29 #include <stdio.h>
30 #include <stdlib.h>
31 #include <string.h>
32 #include <sys/prctl.h>
33 #include <sys/stat.h>
34 #include <sys/times.h>
35 #include <time.h>
36 #include <unistd.h>
37
38 #include "wrappers.h"
39
usage(const char * const argv0)40 static void usage(const char *const argv0)
41 {
42 printf("Usage:\n");
43 printf(" %s [OPTIONS]\n", argv0);
44 printf("\n");
45 printf(" Benchmark expensive Landlock checks for D nested dirs\n");
46 printf("\n");
47 printf("Options:\n");
48 printf(" -h help\n");
49 printf(" -L disable Landlock (as a baseline)\n");
50 printf(" -d D set directory depth to D\n");
51 printf(" -n N set number of benchmark iterations to N\n");
52 }
53
54 /*
55 * Build a deep directory, enforce Landlock and return the FD to the
56 * deepest dir. On any failure, exit the process with an error.
57 */
build_directory(size_t depth,const bool use_landlock)58 static int build_directory(size_t depth, const bool use_landlock)
59 {
60 const char *path = "d"; /* directory name */
61 int abi, ruleset_fd, curr, prev;
62
63 if (use_landlock) {
64 abi = landlock_create_ruleset(NULL, 0,
65 LANDLOCK_CREATE_RULESET_VERSION);
66 if (abi < 7)
67 err(1, "Landlock ABI too low: got %d, wanted 7+", abi);
68 }
69
70 ruleset_fd = -1;
71 if (use_landlock) {
72 struct landlock_ruleset_attr attr = {
73 .handled_access_fs = LANDLOCK_ACCESS_FS_IOCTL_DEV |
74 LANDLOCK_ACCESS_FS_WRITE_FILE |
75 LANDLOCK_ACCESS_FS_MAKE_REG,
76 };
77 ruleset_fd = landlock_create_ruleset(&attr, sizeof(attr), 0U);
78 if (ruleset_fd < 0)
79 err(1, "landlock_create_ruleset");
80 }
81
82 curr = open(".", O_PATH);
83 if (curr < 0)
84 err(1, "open(.)");
85
86 while (depth--) {
87 if (use_landlock) {
88 struct landlock_path_beneath_attr attr = {
89 .allowed_access = LANDLOCK_ACCESS_FS_IOCTL_DEV,
90 .parent_fd = curr,
91 };
92 if (landlock_add_rule(ruleset_fd,
93 LANDLOCK_RULE_PATH_BENEATH, &attr,
94 0) < 0)
95 err(1, "landlock_add_rule");
96 }
97
98 if (mkdirat(curr, path, 0700) < 0)
99 err(1, "mkdirat(%s)", path);
100
101 prev = curr;
102 curr = openat(curr, path, O_PATH);
103 if (curr < 0)
104 err(1, "openat(%s)", path);
105
106 close(prev);
107 }
108
109 if (use_landlock) {
110 if (prctl(PR_SET_NO_NEW_PRIVS, 1, 0, 0, 0) < 0)
111 err(1, "prctl");
112
113 if (landlock_restrict_self(ruleset_fd, 0) < 0)
114 err(1, "landlock_restrict_self");
115 }
116
117 close(ruleset_fd);
118 return curr;
119 }
120
remove_recursively(const size_t depth)121 static void remove_recursively(const size_t depth)
122 {
123 const char *path = "d"; /* directory name */
124
125 int fd = openat(AT_FDCWD, ".", O_PATH);
126
127 if (fd < 0)
128 err(1, "openat(.)");
129
130 for (size_t i = 0; i < depth - 1; i++) {
131 int oldfd = fd;
132
133 fd = openat(fd, path, O_PATH);
134 if (fd < 0)
135 err(1, "openat(%s)", path);
136 close(oldfd);
137 }
138
139 for (size_t i = 0; i < depth; i++) {
140 if (unlinkat(fd, path, AT_REMOVEDIR) < 0)
141 err(1, "unlinkat(%s)", path);
142 int newfd = openat(fd, "..", O_PATH);
143
144 close(fd);
145 fd = newfd;
146 }
147 close(fd);
148 }
149
main(int argc,char * argv[])150 int main(int argc, char *argv[])
151 {
152 bool use_landlock = true;
153 size_t num_iterations = 100000;
154 size_t num_subdirs = 10000;
155 int c, curr, fd;
156 struct tms start_time, end_time;
157
158 setbuf(stdout, NULL);
159 while ((c = getopt(argc, argv, "hLd:n:")) != -1) {
160 switch (c) {
161 case 'h':
162 usage(argv[0]);
163 return EXIT_SUCCESS;
164 case 'L':
165 use_landlock = false;
166 break;
167 case 'd':
168 num_subdirs = atoi(optarg);
169 break;
170 case 'n':
171 num_iterations = atoi(optarg);
172 break;
173 default:
174 usage(argv[0]);
175 return EXIT_FAILURE;
176 }
177 }
178
179 printf("*** Benchmark ***\n");
180 printf("%zu dirs, %zu iterations, %s Landlock\n", num_subdirs,
181 num_iterations, use_landlock ? "with" : "without");
182
183 if (times(&start_time) == -1)
184 err(1, "times");
185
186 curr = build_directory(num_subdirs, use_landlock);
187
188 for (int i = 0; i < num_iterations; i++) {
189 fd = openat(curr, "file.txt", O_CREAT | O_TRUNC | O_WRONLY,
190 0600);
191 if (use_landlock) {
192 if (fd == 0)
193 errx(1, "openat succeeded, expected EACCES");
194 if (errno != EACCES)
195 err(1, "openat expected EACCES, but got");
196 }
197 if (fd != -1)
198 close(fd);
199 }
200
201 if (times(&end_time) == -1)
202 err(1, "times");
203
204 printf("*** Benchmark concluded ***\n");
205 printf("System: %ld clocks\n",
206 end_time.tms_stime - start_time.tms_stime);
207 printf("User : %ld clocks\n",
208 end_time.tms_utime - start_time.tms_utime);
209 printf("Clocks per second: %ld\n", CLOCKS_PER_SEC);
210
211 close(curr);
212
213 remove_recursively(num_subdirs);
214 }
215