[v5] getcwd: Set errno to ERANGE for size == 1 (CVE-2021-3999)
Checks
Context |
Check |
Description |
dj/TryBot-apply_patch |
success
|
Patch applied to master at the time it was sent
|
dj/TryBot-32bit |
success
|
Build for i686
|
Commit Message
No valid path returned by getcwd would fit into 1 byte, so reject the
size early and return NULL with errno set to ERANGE. This change is
prompted by CVE-2021-3999, which describes a single byte buffer
underflow and overflow when all of the following conditions are met:
- The buffer size (i.e. the second argument of getcwd) is 1 byte
- The current working directory is too long
- '/' is also mounted on the current working directory
Sequence of events:
- In sysdeps/unix/sysv/linux/getcwd.c, the syscall returns ENAMETOOLONG
because the linux kernel checks for name length before it checks
buffer size
- The code falls back to the generic getcwd in sysdeps/posix
- In the generic func, the buf[0] is set to '\0' on line 250
- this while loop on line 262 is bypassed:
while (!(thisdev == rootdev && thisino == rootino))
since the rootfs (/) is bind mounted onto the directory and the flow
goes on to line 449, where it puts a '/' in the byte before the
buffer.
- Finally on line 458, it moves 2 bytes (the underflowed byte and the
'\0') to the buf[0] and buf[1], resulting in a 1 byte buffer overflow.
- buf is returned on line 469 and errno is not set.
This resolves BZ #28769.
Reviewed-by: Andreas Schwab <schwab@linux-m68k.org>
Reviewed-by: Adhemerval Zanella <adhemerval.zanella@linaro.org>
Signed-off-by: Qualys Security Advisory <qsa@qualys.com>
Signed-off-by: Siddhesh Poyarekar <siddhesh@sourceware.org>
---
NEWS | 6 +
sysdeps/posix/getcwd.c | 7 +
sysdeps/unix/sysv/linux/Makefile | 7 +-
.../unix/sysv/linux/tst-getcwd-smallbuff.c | 241 ++++++++++++++++++
4 files changed, 260 insertions(+), 1 deletion(-)
create mode 100644 sysdeps/unix/sysv/linux/tst-getcwd-smallbuff.c
Comments
On 21/01/2022 23:34, Siddhesh Poyarekar via Libc-alpha wrote:
> No valid path returned by getcwd would fit into 1 byte, so reject the
> size early and return NULL with errno set to ERANGE. This change is
> prompted by CVE-2021-3999, which describes a single byte buffer
> underflow and overflow when all of the following conditions are met:
>
> - The buffer size (i.e. the second argument of getcwd) is 1 byte
> - The current working directory is too long
> - '/' is also mounted on the current working directory
>
> Sequence of events:
>
> - In sysdeps/unix/sysv/linux/getcwd.c, the syscall returns ENAMETOOLONG
> because the linux kernel checks for name length before it checks
> buffer size
>
> - The code falls back to the generic getcwd in sysdeps/posix
>
> - In the generic func, the buf[0] is set to '\0' on line 250
>
> - this while loop on line 262 is bypassed:
>
> while (!(thisdev == rootdev && thisino == rootino))
>
> since the rootfs (/) is bind mounted onto the directory and the flow
> goes on to line 449, where it puts a '/' in the byte before the
> buffer.
>
> - Finally on line 458, it moves 2 bytes (the underflowed byte and the
> '\0') to the buf[0] and buf[1], resulting in a 1 byte buffer overflow.
>
> - buf is returned on line 469 and errno is not set.
>
> This resolves BZ #28769.
>
> Reviewed-by: Andreas Schwab <schwab@linux-m68k.org>
> Reviewed-by: Adhemerval Zanella <adhemerval.zanella@linaro.org>
> Signed-off-by: Qualys Security Advisory <qsa@qualys.com>
> Signed-off-by: Siddhesh Poyarekar <siddhesh@sourceware.org>
Pushed now since updates were trivial and Adhemerval and Andreas had
already acked the rest.
Thanks,
Siddhesh
> ---
> NEWS | 6 +
> sysdeps/posix/getcwd.c | 7 +
> sysdeps/unix/sysv/linux/Makefile | 7 +-
> .../unix/sysv/linux/tst-getcwd-smallbuff.c | 241 ++++++++++++++++++
> 4 files changed, 260 insertions(+), 1 deletion(-)
> create mode 100644 sysdeps/unix/sysv/linux/tst-getcwd-smallbuff.c
>
> diff --git a/NEWS b/NEWS
> index 4c392a445e..07e9eac52d 100644
> --- a/NEWS
> +++ b/NEWS
> @@ -170,6 +170,12 @@ Security related changes:
> function could result in a memory leak and potential access of
> uninitialized memory. Reported by Qualys.
>
> + CVE-2021-3999: Passing a buffer of size exactly 1 byte to the getcwd
> + function may result in an off-by-one buffer underflow and overflow
> + when the current working directory is longer than PATH_MAX and also
> + corresponds to the / directory through an unprivileged mount
> + namespace. Reported by Qualys.
> +
> The following bugs are resolved with this release:
>
> [The release manager will add the list generated by
> diff --git a/sysdeps/posix/getcwd.c b/sysdeps/posix/getcwd.c
> index e147a31a81..9d5787b6f4 100644
> --- a/sysdeps/posix/getcwd.c
> +++ b/sysdeps/posix/getcwd.c
> @@ -187,6 +187,13 @@ __getcwd_generic (char *buf, size_t size)
> size_t allocated = size;
> size_t used;
>
> + /* A size of 1 byte is never useful. */
> + if (allocated == 1)
> + {
> + __set_errno (ERANGE);
> + return NULL;
> + }
> +
> #if HAVE_MINIMALLY_WORKING_GETCWD
> /* If AT_FDCWD is not defined, the algorithm below is O(N**2) and
> this is much slower than the system getcwd (at least on
> diff --git a/sysdeps/unix/sysv/linux/Makefile b/sysdeps/unix/sysv/linux/Makefile
> index 85fc8cbf75..7ca9350c99 100644
> --- a/sysdeps/unix/sysv/linux/Makefile
> +++ b/sysdeps/unix/sysv/linux/Makefile
> @@ -346,7 +346,12 @@ sysdep_routines += xstatconv internal_statvfs \
>
> sysdep_headers += bits/fcntl-linux.h
>
> -tests += tst-fallocate tst-fallocate64 tst-o_path-locks
> +tests += \
> + tst-fallocate \
> + tst-fallocate64 \
> + tst-getcwd-smallbuff \
> + tst-o_path-locks \
> +# tests
> endif
>
> ifeq ($(subdir),elf)
> diff --git a/sysdeps/unix/sysv/linux/tst-getcwd-smallbuff.c b/sysdeps/unix/sysv/linux/tst-getcwd-smallbuff.c
> new file mode 100644
> index 0000000000..d460d6e766
> --- /dev/null
> +++ b/sysdeps/unix/sysv/linux/tst-getcwd-smallbuff.c
> @@ -0,0 +1,241 @@
> +/* Verify that getcwd returns ERANGE for size 1 byte and does not underflow
> + buffer when the CWD is too long and is also a mount target of /. See bug
> + #28769 or CVE-2021-3999 for more context.
> + Copyright The GNU Toolchain Authors.
> + This file is part of the GNU C Library.
> +
> + The GNU C Library is free software; you can redistribute it and/or
> + modify it under the terms of the GNU Lesser General Public
> + License as published by the Free Software Foundation; either
> + version 2.1 of the License, or (at your option) any later version.
> +
> + The GNU C Library is distributed in the hope that it will be useful,
> + but WITHOUT ANY WARRANTY; without even the implied warranty of
> + MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
> + Lesser General Public License for more details.
> +
> + You should have received a copy of the GNU Lesser General Public
> + License along with the GNU C Library; if not, see
> + <https://www.gnu.org/licenses/>. */
> +
> +#include <errno.h>
> +#include <fcntl.h>
> +#include <intprops.h>
> +#include <limits.h>
> +#include <stdio.h>
> +#include <stdlib.h>
> +#include <string.h>
> +#include <sys/mount.h>
> +#include <sys/stat.h>
> +#include <sys/types.h>
> +#include <sys/wait.h>
> +
> +#include <sys/socket.h>
> +#include <sys/un.h>
> +#include <support/check.h>
> +#include <support/temp_file.h>
> +#include <support/xsched.h>
> +#include <support/xunistd.h>
> +
> +static char *base;
> +#define BASENAME "tst-getcwd-smallbuff"
> +#define MOUNT_NAME "mpoint"
> +static int sockfd[2];
> +
> +static void
> +do_cleanup (void)
> +{
> + support_chdir_toolong_temp_directory (base);
> + TEST_VERIFY_EXIT (rmdir (MOUNT_NAME) == 0);
> + free (base);
> +}
> +
> +static void
> +send_fd (const int sock, const int fd)
> +{
> + struct msghdr msg = {0};
> + union
> + {
> + struct cmsghdr hdr;
> + char buf[CMSG_SPACE (sizeof (int))];
> + } cmsgbuf = {0};
> + struct cmsghdr *cmsg;
> + struct iovec vec;
> + char ch = 'A';
> + ssize_t n;
> +
> + msg.msg_control = &cmsgbuf.buf;
> + msg.msg_controllen = sizeof (cmsgbuf.buf);
> +
> + cmsg = CMSG_FIRSTHDR (&msg);
> + cmsg->cmsg_len = CMSG_LEN (sizeof (int));
> + cmsg->cmsg_level = SOL_SOCKET;
> + cmsg->cmsg_type = SCM_RIGHTS;
> + memcpy (CMSG_DATA (cmsg), &fd, sizeof (fd));
> +
> + vec.iov_base = &ch;
> + vec.iov_len = 1;
> + msg.msg_iov = &vec;
> + msg.msg_iovlen = 1;
> +
> + while ((n = sendmsg (sock, &msg, 0)) == -1 && errno == EINTR);
> +
> + TEST_VERIFY_EXIT (n == 1);
> +}
> +
> +static int
> +recv_fd (const int sock)
> +{
> + struct msghdr msg = {0};
> + union
> + {
> + struct cmsghdr hdr;
> + char buf[CMSG_SPACE(sizeof(int))];
> + } cmsgbuf = {0};
> + struct cmsghdr *cmsg;
> + struct iovec vec;
> + ssize_t n;
> + char ch = '\0';
> + int fd = -1;
> +
> + vec.iov_base = &ch;
> + vec.iov_len = 1;
> + msg.msg_iov = &vec;
> + msg.msg_iovlen = 1;
> +
> + msg.msg_control = &cmsgbuf.buf;
> + msg.msg_controllen = sizeof (cmsgbuf.buf);
> +
> + while ((n = recvmsg (sock, &msg, 0)) == -1 && errno == EINTR);
> + if (n != 1 || ch != 'A')
> + return -1;
> +
> + cmsg = CMSG_FIRSTHDR (&msg);
> + if (cmsg == NULL)
> + return -1;
> + if (cmsg->cmsg_type != SCM_RIGHTS)
> + return -1;
> + memcpy (&fd, CMSG_DATA (cmsg), sizeof (fd));
> + if (fd < 0)
> + return -1;
> + return fd;
> +}
> +
> +static int
> +child_func (void * const arg)
> +{
> + xclose (sockfd[0]);
> + const int sock = sockfd[1];
> + char ch;
> +
> + TEST_VERIFY_EXIT (read (sock, &ch, 1) == 1);
> + TEST_VERIFY_EXIT (ch == '1');
> +
> + if (mount ("/", MOUNT_NAME, NULL, MS_BIND | MS_REC, NULL))
> + FAIL_EXIT1 ("mount failed: %m\n");
> + const int fd = xopen ("mpoint",
> + O_RDONLY | O_PATH | O_DIRECTORY | O_NOFOLLOW, 0);
> +
> + send_fd (sock, fd);
> + xclose (fd);
> +
> + TEST_VERIFY_EXIT (read (sock, &ch, 1) == 1);
> + TEST_VERIFY_EXIT (ch == 'a');
> +
> + xclose (sock);
> + return 0;
> +}
> +
> +static void
> +update_map (char * const mapping, const char * const map_file)
> +{
> + const size_t map_len = strlen (mapping);
> +
> + const int fd = xopen (map_file, O_WRONLY, 0);
> + xwrite (fd, mapping, map_len);
> + xclose (fd);
> +}
> +
> +static void
> +proc_setgroups_write (const long child_pid, const char * const str)
> +{
> + const size_t str_len = strlen(str);
> +
> + char setgroups_path[sizeof ("/proc//setgroups") + INT_STRLEN_BOUND (long)];
> +
> + snprintf (setgroups_path, sizeof (setgroups_path),
> + "/proc/%ld/setgroups", child_pid);
> +
> + const int fd = open (setgroups_path, O_WRONLY);
> +
> + if (fd < 0)
> + {
> + TEST_VERIFY_EXIT (errno == ENOENT);
> + FAIL_UNSUPPORTED ("/proc/%ld/setgroups not found\n", child_pid);
> + }
> +
> + xwrite (fd, str, str_len);
> + xclose(fd);
> +}
> +
> +static char child_stack[1024 * 1024];
> +
> +int
> +do_test (void)
> +{
> + base = support_create_and_chdir_toolong_temp_directory (BASENAME);
> +
> + xmkdir (MOUNT_NAME, S_IRWXU);
> + atexit (do_cleanup);
> +
> + TEST_VERIFY_EXIT (socketpair (AF_UNIX, SOCK_STREAM, 0, sockfd) == 0);
> + pid_t child_pid = xclone (child_func, NULL, child_stack,
> + sizeof (child_stack),
> + CLONE_NEWUSER | CLONE_NEWNS | SIGCHLD);
> +
> + xclose (sockfd[1]);
> + const int sock = sockfd[0];
> +
> + char map_path[sizeof ("/proc//uid_map") + INT_STRLEN_BOUND (long)];
> + char map_buf[sizeof ("0 1") + INT_STRLEN_BOUND (long)];
> +
> + snprintf (map_path, sizeof (map_path), "/proc/%ld/uid_map",
> + (long) child_pid);
> + snprintf (map_buf, sizeof (map_buf), "0 %ld 1", (long) getuid());
> + update_map (map_buf, map_path);
> +
> + proc_setgroups_write ((long) child_pid, "deny");
> + snprintf (map_path, sizeof (map_path), "/proc/%ld/gid_map",
> + (long) child_pid);
> + snprintf (map_buf, sizeof (map_buf), "0 %ld 1", (long) getgid());
> + update_map (map_buf, map_path);
> +
> + TEST_VERIFY_EXIT (send (sock, "1", 1, MSG_NOSIGNAL) == 1);
> + const int fd = recv_fd (sock);
> + TEST_VERIFY_EXIT (fd >= 0);
> + TEST_VERIFY_EXIT (fchdir (fd) == 0);
> +
> + static char buf[2 * 10 + 1];
> + memset (buf, 'A', sizeof (buf));
> +
> + /* Finally, call getcwd and check if it resulted in a buffer underflow. */
> + char * cwd = getcwd (buf + sizeof (buf) / 2, 1);
> + TEST_VERIFY (cwd == NULL);
> + TEST_VERIFY (errno == ERANGE);
> +
> + for (int i = 0; i < sizeof (buf); i++)
> + if (buf[i] != 'A')
> + {
> + printf ("buf[%d] = %02x\n", i, (unsigned int) buf[i]);
> + support_record_failure ();
> + }
> +
> + TEST_VERIFY_EXIT (send (sock, "a", 1, MSG_NOSIGNAL) == 1);
> + xclose (sock);
> + TEST_VERIFY_EXIT (xwaitpid (child_pid, NULL, 0) == child_pid);
> +
> + return 0;
> +}
> +
> +#define CLEANUP_HANDLER do_cleanup
> +#include <support/test-driver.c>
@@ -170,6 +170,12 @@ Security related changes:
function could result in a memory leak and potential access of
uninitialized memory. Reported by Qualys.
+ CVE-2021-3999: Passing a buffer of size exactly 1 byte to the getcwd
+ function may result in an off-by-one buffer underflow and overflow
+ when the current working directory is longer than PATH_MAX and also
+ corresponds to the / directory through an unprivileged mount
+ namespace. Reported by Qualys.
+
The following bugs are resolved with this release:
[The release manager will add the list generated by
@@ -187,6 +187,13 @@ __getcwd_generic (char *buf, size_t size)
size_t allocated = size;
size_t used;
+ /* A size of 1 byte is never useful. */
+ if (allocated == 1)
+ {
+ __set_errno (ERANGE);
+ return NULL;
+ }
+
#if HAVE_MINIMALLY_WORKING_GETCWD
/* If AT_FDCWD is not defined, the algorithm below is O(N**2) and
this is much slower than the system getcwd (at least on
@@ -346,7 +346,12 @@ sysdep_routines += xstatconv internal_statvfs \
sysdep_headers += bits/fcntl-linux.h
-tests += tst-fallocate tst-fallocate64 tst-o_path-locks
+tests += \
+ tst-fallocate \
+ tst-fallocate64 \
+ tst-getcwd-smallbuff \
+ tst-o_path-locks \
+# tests
endif
ifeq ($(subdir),elf)
new file mode 100644
@@ -0,0 +1,241 @@
+/* Verify that getcwd returns ERANGE for size 1 byte and does not underflow
+ buffer when the CWD is too long and is also a mount target of /. See bug
+ #28769 or CVE-2021-3999 for more context.
+ Copyright The GNU Toolchain Authors.
+ This file is part of the GNU C Library.
+
+ The GNU C Library is free software; you can redistribute it and/or
+ modify it under the terms of the GNU Lesser General Public
+ License as published by the Free Software Foundation; either
+ version 2.1 of the License, or (at your option) any later version.
+
+ The GNU C Library is distributed in the hope that it will be useful,
+ but WITHOUT ANY WARRANTY; without even the implied warranty of
+ MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
+ Lesser General Public License for more details.
+
+ You should have received a copy of the GNU Lesser General Public
+ License along with the GNU C Library; if not, see
+ <https://www.gnu.org/licenses/>. */
+
+#include <errno.h>
+#include <fcntl.h>
+#include <intprops.h>
+#include <limits.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <sys/mount.h>
+#include <sys/stat.h>
+#include <sys/types.h>
+#include <sys/wait.h>
+
+#include <sys/socket.h>
+#include <sys/un.h>
+#include <support/check.h>
+#include <support/temp_file.h>
+#include <support/xsched.h>
+#include <support/xunistd.h>
+
+static char *base;
+#define BASENAME "tst-getcwd-smallbuff"
+#define MOUNT_NAME "mpoint"
+static int sockfd[2];
+
+static void
+do_cleanup (void)
+{
+ support_chdir_toolong_temp_directory (base);
+ TEST_VERIFY_EXIT (rmdir (MOUNT_NAME) == 0);
+ free (base);
+}
+
+static void
+send_fd (const int sock, const int fd)
+{
+ struct msghdr msg = {0};
+ union
+ {
+ struct cmsghdr hdr;
+ char buf[CMSG_SPACE (sizeof (int))];
+ } cmsgbuf = {0};
+ struct cmsghdr *cmsg;
+ struct iovec vec;
+ char ch = 'A';
+ ssize_t n;
+
+ msg.msg_control = &cmsgbuf.buf;
+ msg.msg_controllen = sizeof (cmsgbuf.buf);
+
+ cmsg = CMSG_FIRSTHDR (&msg);
+ cmsg->cmsg_len = CMSG_LEN (sizeof (int));
+ cmsg->cmsg_level = SOL_SOCKET;
+ cmsg->cmsg_type = SCM_RIGHTS;
+ memcpy (CMSG_DATA (cmsg), &fd, sizeof (fd));
+
+ vec.iov_base = &ch;
+ vec.iov_len = 1;
+ msg.msg_iov = &vec;
+ msg.msg_iovlen = 1;
+
+ while ((n = sendmsg (sock, &msg, 0)) == -1 && errno == EINTR);
+
+ TEST_VERIFY_EXIT (n == 1);
+}
+
+static int
+recv_fd (const int sock)
+{
+ struct msghdr msg = {0};
+ union
+ {
+ struct cmsghdr hdr;
+ char buf[CMSG_SPACE(sizeof(int))];
+ } cmsgbuf = {0};
+ struct cmsghdr *cmsg;
+ struct iovec vec;
+ ssize_t n;
+ char ch = '\0';
+ int fd = -1;
+
+ vec.iov_base = &ch;
+ vec.iov_len = 1;
+ msg.msg_iov = &vec;
+ msg.msg_iovlen = 1;
+
+ msg.msg_control = &cmsgbuf.buf;
+ msg.msg_controllen = sizeof (cmsgbuf.buf);
+
+ while ((n = recvmsg (sock, &msg, 0)) == -1 && errno == EINTR);
+ if (n != 1 || ch != 'A')
+ return -1;
+
+ cmsg = CMSG_FIRSTHDR (&msg);
+ if (cmsg == NULL)
+ return -1;
+ if (cmsg->cmsg_type != SCM_RIGHTS)
+ return -1;
+ memcpy (&fd, CMSG_DATA (cmsg), sizeof (fd));
+ if (fd < 0)
+ return -1;
+ return fd;
+}
+
+static int
+child_func (void * const arg)
+{
+ xclose (sockfd[0]);
+ const int sock = sockfd[1];
+ char ch;
+
+ TEST_VERIFY_EXIT (read (sock, &ch, 1) == 1);
+ TEST_VERIFY_EXIT (ch == '1');
+
+ if (mount ("/", MOUNT_NAME, NULL, MS_BIND | MS_REC, NULL))
+ FAIL_EXIT1 ("mount failed: %m\n");
+ const int fd = xopen ("mpoint",
+ O_RDONLY | O_PATH | O_DIRECTORY | O_NOFOLLOW, 0);
+
+ send_fd (sock, fd);
+ xclose (fd);
+
+ TEST_VERIFY_EXIT (read (sock, &ch, 1) == 1);
+ TEST_VERIFY_EXIT (ch == 'a');
+
+ xclose (sock);
+ return 0;
+}
+
+static void
+update_map (char * const mapping, const char * const map_file)
+{
+ const size_t map_len = strlen (mapping);
+
+ const int fd = xopen (map_file, O_WRONLY, 0);
+ xwrite (fd, mapping, map_len);
+ xclose (fd);
+}
+
+static void
+proc_setgroups_write (const long child_pid, const char * const str)
+{
+ const size_t str_len = strlen(str);
+
+ char setgroups_path[sizeof ("/proc//setgroups") + INT_STRLEN_BOUND (long)];
+
+ snprintf (setgroups_path, sizeof (setgroups_path),
+ "/proc/%ld/setgroups", child_pid);
+
+ const int fd = open (setgroups_path, O_WRONLY);
+
+ if (fd < 0)
+ {
+ TEST_VERIFY_EXIT (errno == ENOENT);
+ FAIL_UNSUPPORTED ("/proc/%ld/setgroups not found\n", child_pid);
+ }
+
+ xwrite (fd, str, str_len);
+ xclose(fd);
+}
+
+static char child_stack[1024 * 1024];
+
+int
+do_test (void)
+{
+ base = support_create_and_chdir_toolong_temp_directory (BASENAME);
+
+ xmkdir (MOUNT_NAME, S_IRWXU);
+ atexit (do_cleanup);
+
+ TEST_VERIFY_EXIT (socketpair (AF_UNIX, SOCK_STREAM, 0, sockfd) == 0);
+ pid_t child_pid = xclone (child_func, NULL, child_stack,
+ sizeof (child_stack),
+ CLONE_NEWUSER | CLONE_NEWNS | SIGCHLD);
+
+ xclose (sockfd[1]);
+ const int sock = sockfd[0];
+
+ char map_path[sizeof ("/proc//uid_map") + INT_STRLEN_BOUND (long)];
+ char map_buf[sizeof ("0 1") + INT_STRLEN_BOUND (long)];
+
+ snprintf (map_path, sizeof (map_path), "/proc/%ld/uid_map",
+ (long) child_pid);
+ snprintf (map_buf, sizeof (map_buf), "0 %ld 1", (long) getuid());
+ update_map (map_buf, map_path);
+
+ proc_setgroups_write ((long) child_pid, "deny");
+ snprintf (map_path, sizeof (map_path), "/proc/%ld/gid_map",
+ (long) child_pid);
+ snprintf (map_buf, sizeof (map_buf), "0 %ld 1", (long) getgid());
+ update_map (map_buf, map_path);
+
+ TEST_VERIFY_EXIT (send (sock, "1", 1, MSG_NOSIGNAL) == 1);
+ const int fd = recv_fd (sock);
+ TEST_VERIFY_EXIT (fd >= 0);
+ TEST_VERIFY_EXIT (fchdir (fd) == 0);
+
+ static char buf[2 * 10 + 1];
+ memset (buf, 'A', sizeof (buf));
+
+ /* Finally, call getcwd and check if it resulted in a buffer underflow. */
+ char * cwd = getcwd (buf + sizeof (buf) / 2, 1);
+ TEST_VERIFY (cwd == NULL);
+ TEST_VERIFY (errno == ERANGE);
+
+ for (int i = 0; i < sizeof (buf); i++)
+ if (buf[i] != 'A')
+ {
+ printf ("buf[%d] = %02x\n", i, (unsigned int) buf[i]);
+ support_record_failure ();
+ }
+
+ TEST_VERIFY_EXIT (send (sock, "a", 1, MSG_NOSIGNAL) == 1);
+ xclose (sock);
+ TEST_VERIFY_EXIT (xwaitpid (child_pid, NULL, 0) == child_pid);
+
+ return 0;
+}
+
+#define CLEANUP_HANDLER do_cleanup
+#include <support/test-driver.c>