1 /* Verify that getcwd returns ERANGE for size 1 byte and does not underflow
2 buffer when the CWD is too long and is also a mount target of /. See bug
3 #28769 or CVE-2021-3999 for more context.
4 Copyright The GNU Toolchain Authors.
5 This file is part of the GNU C Library.
6
7 The GNU C Library is free software; you can redistribute it and/or
8 modify it under the terms of the GNU Lesser General Public
9 License as published by the Free Software Foundation; either
10 version 2.1 of the License, or (at your option) any later version.
11
12 The GNU C Library is distributed in the hope that it will be useful,
13 but WITHOUT ANY WARRANTY; without even the implied warranty of
14 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
15 Lesser General Public License for more details.
16
17 You should have received a copy of the GNU Lesser General Public
18 License along with the GNU C Library; if not, see
19 <https://www.gnu.org/licenses/>. */
20
21 #include <errno.h>
22 #include <fcntl.h>
23 #include <intprops.h>
24 #include <limits.h>
25 #include <stdio.h>
26 #include <stdlib.h>
27 #include <string.h>
28 #include <sys/mount.h>
29 #include <sys/stat.h>
30 #include <sys/types.h>
31 #include <sys/wait.h>
32
33 #include <sys/socket.h>
34 #include <sys/un.h>
35 #include <support/check.h>
36 #include <support/temp_file.h>
37 #include <support/test-driver.h>
38 #include <support/xsched.h>
39 #include <support/xunistd.h>
40
41 static char *base;
42 #define BASENAME "tst-getcwd-smallbuff"
43 #define MOUNT_NAME "mpoint"
44 static int sockfd[2];
45
46 static void
47 do_cleanup (void)
48 {
49 support_chdir_toolong_temp_directory (base);
50 TEST_VERIFY_EXIT (rmdir (MOUNT_NAME) == 0);
51 free (base);
52 }
53
54 static void
55 send_fd (const int sock, const int fd)
56 {
57 struct msghdr msg = {0};
58 union
59 {
60 struct cmsghdr hdr;
61 char buf[CMSG_SPACE (sizeof (int))];
62 } cmsgbuf = {0};
63 struct cmsghdr *cmsg;
64 struct iovec vec;
65 char ch = 'A';
66 ssize_t n;
67
68 msg.msg_control = &cmsgbuf.buf;
69 msg.msg_controllen = sizeof (cmsgbuf.buf);
70
71 cmsg = CMSG_FIRSTHDR (&msg);
72 cmsg->cmsg_len = CMSG_LEN (sizeof (int));
73 cmsg->cmsg_level = SOL_SOCKET;
74 cmsg->cmsg_type = SCM_RIGHTS;
75 memcpy (CMSG_DATA (cmsg), &fd, sizeof (fd));
76
77 vec.iov_base = &ch;
78 vec.iov_len = 1;
79 msg.msg_iov = &vec;
80 msg.msg_iovlen = 1;
81
82 while ((n = sendmsg (sock, &msg, 0)) == -1 && errno == EINTR);
83
84 TEST_VERIFY_EXIT (n == 1);
85 }
86
87 static int
88 recv_fd (const int sock)
89 {
90 struct msghdr msg = {0};
91 union
92 {
93 struct cmsghdr hdr;
94 char buf[CMSG_SPACE(sizeof(int))];
95 } cmsgbuf = {0};
96 struct cmsghdr *cmsg;
97 struct iovec vec;
98 ssize_t n;
99 char ch = '\0';
100 int fd = -1;
101
102 vec.iov_base = &ch;
103 vec.iov_len = 1;
104 msg.msg_iov = &vec;
105 msg.msg_iovlen = 1;
106
107 msg.msg_control = &cmsgbuf.buf;
108 msg.msg_controllen = sizeof (cmsgbuf.buf);
109
110 while ((n = recvmsg (sock, &msg, 0)) == -1 && errno == EINTR);
111 if (n != 1 || ch != 'A')
112 return -1;
113
114 cmsg = CMSG_FIRSTHDR (&msg);
115 if (cmsg == NULL)
116 return -1;
117 if (cmsg->cmsg_type != SCM_RIGHTS)
118 return -1;
119 memcpy (&fd, CMSG_DATA (cmsg), sizeof (fd));
120 if (fd < 0)
121 return -1;
122 return fd;
123 }
124
125 static int
126 child_func (void * const arg)
127 {
128 xclose (sockfd[0]);
129 const int sock = sockfd[1];
130 char ch;
131
132 TEST_VERIFY_EXIT (read (sock, &ch, 1) == 1);
133 TEST_VERIFY_EXIT (ch == '1');
134
135 if (mount ("/", MOUNT_NAME, NULL, MS_BIND | MS_REC, NULL))
136 FAIL_EXIT1 ("mount failed: %m\n");
137 const int fd = xopen ("mpoint",
138 O_RDONLY | O_PATH | O_DIRECTORY | O_NOFOLLOW, 0);
139
140 send_fd (sock, fd);
141 xclose (fd);
142
143 TEST_VERIFY_EXIT (read (sock, &ch, 1) == 1);
144 TEST_VERIFY_EXIT (ch == 'a');
145
146 xclose (sock);
147 return 0;
148 }
149
150 static void
151 update_map (char * const mapping, const char * const map_file)
152 {
153 const size_t map_len = strlen (mapping);
154
155 const int fd = xopen (map_file, O_WRONLY, 0);
156 xwrite (fd, mapping, map_len);
157 xclose (fd);
158 }
159
160 static void
161 proc_setgroups_write (const long child_pid, const char * const str)
162 {
163 const size_t str_len = strlen(str);
164
165 char setgroups_path[sizeof ("/proc//setgroups") + INT_STRLEN_BOUND (long)];
166
167 snprintf (setgroups_path, sizeof (setgroups_path),
168 "/proc/%ld/setgroups", child_pid);
169
170 const int fd = open (setgroups_path, O_WRONLY);
171
172 if (fd < 0)
173 {
174 TEST_VERIFY_EXIT (errno == ENOENT);
175 FAIL_UNSUPPORTED ("/proc/%ld/setgroups not found\n", child_pid);
176 }
177
178 xwrite (fd, str, str_len);
179 xclose(fd);
180 }
181
182 static char child_stack[1024 * 1024];
183
184 int
185 do_test (void)
186 {
187 base = support_create_and_chdir_toolong_temp_directory (BASENAME);
188
189 xmkdir (MOUNT_NAME, S_IRWXU);
190 atexit (do_cleanup);
191
192 /* Check whether user namespaces are supported. */
193 {
194 pid_t pid = xfork ();
195 if (pid == 0)
196 {
197 if (unshare (CLONE_NEWUSER | CLONE_NEWNS) != 0)
198 _exit (EXIT_UNSUPPORTED);
199 else
200 _exit (0);
201 }
202 int status;
203 xwaitpid (pid, &status, 0);
204 TEST_VERIFY_EXIT (WIFEXITED (status));
205 if (WEXITSTATUS (status) != 0)
206 return WEXITSTATUS (status);
207 }
208
209 TEST_VERIFY_EXIT (socketpair (AF_UNIX, SOCK_STREAM, 0, sockfd) == 0);
210 pid_t child_pid = xclone (child_func, NULL, child_stack,
211 sizeof (child_stack),
212 CLONE_NEWUSER | CLONE_NEWNS | SIGCHLD);
213
214 xclose (sockfd[1]);
215 const int sock = sockfd[0];
216
217 char map_path[sizeof ("/proc//uid_map") + INT_STRLEN_BOUND (long)];
218 char map_buf[sizeof ("0 1") + INT_STRLEN_BOUND (long)];
219
220 snprintf (map_path, sizeof (map_path), "/proc/%ld/uid_map",
221 (long) child_pid);
222 snprintf (map_buf, sizeof (map_buf), "0 %ld 1", (long) getuid());
223 update_map (map_buf, map_path);
224
225 proc_setgroups_write ((long) child_pid, "deny");
226 snprintf (map_path, sizeof (map_path), "/proc/%ld/gid_map",
227 (long) child_pid);
228 snprintf (map_buf, sizeof (map_buf), "0 %ld 1", (long) getgid());
229 update_map (map_buf, map_path);
230
231 TEST_VERIFY_EXIT (send (sock, "1", 1, MSG_NOSIGNAL) == 1);
232 const int fd = recv_fd (sock);
233 TEST_VERIFY_EXIT (fd >= 0);
234 TEST_VERIFY_EXIT (fchdir (fd) == 0);
235
236 static char buf[2 * 10 + 1];
237 memset (buf, 'A', sizeof (buf));
238
239 /* Finally, call getcwd and check if it resulted in a buffer underflow. */
240 char * cwd = getcwd (buf + sizeof (buf) / 2, 1);
241 TEST_VERIFY (cwd == NULL);
242 TEST_VERIFY (errno == ERANGE);
243
244 for (int i = 0; i < sizeof (buf); i++)
245 if (buf[i] != 'A')
246 {
247 printf ("buf[%d] = %02x\n", i, (unsigned int) buf[i]);
248 support_record_failure ();
249 }
250
251 TEST_VERIFY_EXIT (send (sock, "a", 1, MSG_NOSIGNAL) == 1);
252 xclose (sock);
253 TEST_VERIFY_EXIT (xwaitpid (child_pid, NULL, 0) == child_pid);
254
255 return 0;
256 }
257
258 #define CLEANUP_HANDLER do_cleanup
259 #include <support/test-driver.c>