260 lines
6.4 KiB
C
260 lines
6.4 KiB
C
/* Verify that getcwd returns ERANGE for size 1 byte and does not underflow
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buffer when the CWD is too long and is also a mount target of /. See bug
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#28769 or CVE-2021-3999 for more context.
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Copyright The GNU Toolchain Authors.
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This file is part of the GNU C Library.
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The GNU C Library is free software; you can redistribute it and/or
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modify it under the terms of the GNU Lesser General Public
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License as published by the Free Software Foundation; either
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version 2.1 of the License, or (at your option) any later version.
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The GNU C Library is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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Lesser General Public License for more details.
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You should have received a copy of the GNU Lesser General Public
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License along with the GNU C Library; if not, see
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<https://www.gnu.org/licenses/>. */
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#include <errno.h>
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#include <fcntl.h>
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#include <intprops.h>
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#include <limits.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/mount.h>
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#include <sys/stat.h>
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#include <sys/types.h>
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#include <sys/wait.h>
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#include <sys/socket.h>
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#include <sys/un.h>
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#include <support/check.h>
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#include <support/temp_file.h>
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#include <support/test-driver.h>
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#include <support/xsched.h>
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#include <support/xunistd.h>
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static char *base;
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#define BASENAME "tst-getcwd-smallbuff"
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#define MOUNT_NAME "mpoint"
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static int sockfd[2];
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static void
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do_cleanup (void)
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{
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support_chdir_toolong_temp_directory (base);
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TEST_VERIFY_EXIT (rmdir (MOUNT_NAME) == 0);
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free (base);
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}
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static void
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send_fd (const int sock, const int fd)
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{
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struct msghdr msg = {0};
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union
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{
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struct cmsghdr hdr;
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char buf[CMSG_SPACE (sizeof (int))];
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} cmsgbuf = {0};
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struct cmsghdr *cmsg;
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struct iovec vec;
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char ch = 'A';
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ssize_t n;
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msg.msg_control = &cmsgbuf.buf;
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msg.msg_controllen = sizeof (cmsgbuf.buf);
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cmsg = CMSG_FIRSTHDR (&msg);
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cmsg->cmsg_len = CMSG_LEN (sizeof (int));
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cmsg->cmsg_level = SOL_SOCKET;
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cmsg->cmsg_type = SCM_RIGHTS;
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memcpy (CMSG_DATA (cmsg), &fd, sizeof (fd));
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vec.iov_base = &ch;
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vec.iov_len = 1;
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msg.msg_iov = &vec;
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msg.msg_iovlen = 1;
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while ((n = sendmsg (sock, &msg, 0)) == -1 && errno == EINTR);
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TEST_VERIFY_EXIT (n == 1);
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}
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static int
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recv_fd (const int sock)
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{
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struct msghdr msg = {0};
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union
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{
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struct cmsghdr hdr;
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char buf[CMSG_SPACE(sizeof(int))];
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} cmsgbuf = {0};
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struct cmsghdr *cmsg;
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struct iovec vec;
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ssize_t n;
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char ch = '\0';
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int fd = -1;
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vec.iov_base = &ch;
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vec.iov_len = 1;
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msg.msg_iov = &vec;
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msg.msg_iovlen = 1;
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msg.msg_control = &cmsgbuf.buf;
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msg.msg_controllen = sizeof (cmsgbuf.buf);
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while ((n = recvmsg (sock, &msg, 0)) == -1 && errno == EINTR);
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if (n != 1 || ch != 'A')
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return -1;
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cmsg = CMSG_FIRSTHDR (&msg);
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if (cmsg == NULL)
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return -1;
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if (cmsg->cmsg_type != SCM_RIGHTS)
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return -1;
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memcpy (&fd, CMSG_DATA (cmsg), sizeof (fd));
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if (fd < 0)
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return -1;
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return fd;
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}
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static int
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child_func (void * const arg)
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{
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xclose (sockfd[0]);
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const int sock = sockfd[1];
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char ch;
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TEST_VERIFY_EXIT (read (sock, &ch, 1) == 1);
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TEST_VERIFY_EXIT (ch == '1');
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if (mount ("/", MOUNT_NAME, NULL, MS_BIND | MS_REC, NULL))
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FAIL_EXIT1 ("mount failed: %m\n");
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const int fd = xopen ("mpoint",
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O_RDONLY | O_PATH | O_DIRECTORY | O_NOFOLLOW, 0);
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send_fd (sock, fd);
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xclose (fd);
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TEST_VERIFY_EXIT (read (sock, &ch, 1) == 1);
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TEST_VERIFY_EXIT (ch == 'a');
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xclose (sock);
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return 0;
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}
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static void
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update_map (char * const mapping, const char * const map_file)
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{
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const size_t map_len = strlen (mapping);
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const int fd = xopen (map_file, O_WRONLY, 0);
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xwrite (fd, mapping, map_len);
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xclose (fd);
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}
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static void
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proc_setgroups_write (const long child_pid, const char * const str)
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{
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const size_t str_len = strlen(str);
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char setgroups_path[sizeof ("/proc//setgroups") + INT_STRLEN_BOUND (long)];
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snprintf (setgroups_path, sizeof (setgroups_path),
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"/proc/%ld/setgroups", child_pid);
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const int fd = open (setgroups_path, O_WRONLY);
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if (fd < 0)
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{
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TEST_VERIFY_EXIT (errno == ENOENT);
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FAIL_UNSUPPORTED ("/proc/%ld/setgroups not found\n", child_pid);
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}
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xwrite (fd, str, str_len);
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xclose(fd);
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}
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static char child_stack[1024 * 1024];
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int
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do_test (void)
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{
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base = support_create_and_chdir_toolong_temp_directory (BASENAME);
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xmkdir (MOUNT_NAME, S_IRWXU);
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atexit (do_cleanup);
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/* Check whether user namespaces are supported. */
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{
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pid_t pid = xfork ();
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if (pid == 0)
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{
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if (unshare (CLONE_NEWUSER | CLONE_NEWNS) != 0)
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_exit (EXIT_UNSUPPORTED);
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else
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_exit (0);
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}
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int status;
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xwaitpid (pid, &status, 0);
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TEST_VERIFY_EXIT (WIFEXITED (status));
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if (WEXITSTATUS (status) != 0)
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return WEXITSTATUS (status);
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}
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TEST_VERIFY_EXIT (socketpair (AF_UNIX, SOCK_STREAM, 0, sockfd) == 0);
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pid_t child_pid = xclone (child_func, NULL, child_stack,
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sizeof (child_stack),
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CLONE_NEWUSER | CLONE_NEWNS | SIGCHLD);
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xclose (sockfd[1]);
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const int sock = sockfd[0];
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char map_path[sizeof ("/proc//uid_map") + INT_STRLEN_BOUND (long)];
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char map_buf[sizeof ("0 1") + INT_STRLEN_BOUND (long)];
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snprintf (map_path, sizeof (map_path), "/proc/%ld/uid_map",
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(long) child_pid);
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snprintf (map_buf, sizeof (map_buf), "0 %ld 1", (long) getuid());
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update_map (map_buf, map_path);
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proc_setgroups_write ((long) child_pid, "deny");
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snprintf (map_path, sizeof (map_path), "/proc/%ld/gid_map",
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(long) child_pid);
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snprintf (map_buf, sizeof (map_buf), "0 %ld 1", (long) getgid());
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update_map (map_buf, map_path);
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TEST_VERIFY_EXIT (send (sock, "1", 1, MSG_NOSIGNAL) == 1);
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const int fd = recv_fd (sock);
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TEST_VERIFY_EXIT (fd >= 0);
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TEST_VERIFY_EXIT (fchdir (fd) == 0);
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static char buf[2 * 10 + 1];
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memset (buf, 'A', sizeof (buf));
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/* Finally, call getcwd and check if it resulted in a buffer underflow. */
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char * cwd = getcwd (buf + sizeof (buf) / 2, 1);
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TEST_VERIFY (cwd == NULL);
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TEST_VERIFY (errno == ERANGE);
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for (int i = 0; i < sizeof (buf); i++)
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if (buf[i] != 'A')
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{
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printf ("buf[%d] = %02x\n", i, (unsigned int) buf[i]);
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support_record_failure ();
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}
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TEST_VERIFY_EXIT (send (sock, "a", 1, MSG_NOSIGNAL) == 1);
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xclose (sock);
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TEST_VERIFY_EXIT (xwaitpid (child_pid, NULL, 0) == child_pid);
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return 0;
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}
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#define CLEANUP_HANDLER do_cleanup
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#include <support/test-driver.c>
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