diff options
| -rw-r--r-- | NEWS | 6 | ||||
| -rw-r--r-- | sysdeps/posix/getcwd.c | 7 | ||||
| -rw-r--r-- | sysdeps/unix/sysv/linux/Makefile | 7 | ||||
| -rw-r--r-- | sysdeps/unix/sysv/linux/tst-getcwd-smallbuff.c | 241 |
4 files changed, 260 insertions, 1 deletions
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> |