From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from hall.aurel32.net (hall.aurel32.net [IPv6:2001:bc8:30d7:100::1]) by sourceware.org (Postfix) with ESMTPS id 517AB385803B; Mon, 24 Jan 2022 22:49:09 +0000 (GMT) DMARC-Filter: OpenDMARC Filter v1.4.1 sourceware.org 517AB385803B Authentication-Results: sourceware.org; dmarc=none (p=none dis=none) header.from=aurel32.net Authentication-Results: sourceware.org; spf=none smtp.mailfrom=aurel32.net DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=aurel32.net ; s=202004.hall; h=Content-Transfer-Encoding:MIME-Version:References: In-Reply-To:Message-Id:Date:Subject:Cc:To:From:Content-Type:From:Reply-To: Subject:Content-ID:Content-Description:X-Debbugs-Cc; bh=L/P5bt2q1jm+a8450OlQV3xCsCD9cHdMVVqgKwddsyo=; b=h4enh3iuTHgs2J6QFp0c/TjFgm I6uLWE0gV0IysTUgswjUO01yNwpsL0DeDMjFlcgubdbX5yLmV9tSfUEgg0cpZcCBY5cOOHtV5FHRZ Jke7E9rKxiIzN/45bhc67WPGAKzHArELGMbeuubaf3pPV8bEsBKAqnE3zqw7yNhUcolgvS9QIbVx2 y36sFjbR/Qbwp4Idq6/OMMYorWaY4X9fpG+AgdKWZgGzSJ1hxVxd20zb7oj/R1wOEUGVgv9pywjzM e8vektw/fRLRYCJjP+yrGOxsqB2oxradEvMM3zqv2acL2YgJHgsisuwzPoTJCqkHq0ShF+W/2cbOF Nx1uBQLw==; Received: from [2a01:e34:ec5d:a741:8a4c:7c4e:dc4c:1787] (helo=ohm.rr44.fr) by hall.aurel32.net with esmtpsa (TLS1.3) tls TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384 (Exim 4.94.2) (envelope-from ) id 1nC88y-00FSYL-2D; Mon, 24 Jan 2022 23:49:00 +0100 Received: from aurel32 by ohm.rr44.fr with local (Exim 4.95) (envelope-from ) id 1nC88x-00FwjQ-6s; Mon, 24 Jan 2022 23:48:59 +0100 From: Aurelien Jarno To: libc-stable@sourceware.org Cc: Siddhesh Poyarekar , Andreas Schwab , Adhemerval Zanella , Qualys Security Advisory Subject: [COMMITTED 2.33 5/7] getcwd: Set errno to ERANGE for size == 1 (CVE-2021-3999) Date: Mon, 24 Jan 2022 23:48:55 +0100 Message-Id: <20220124224857.3799610-5-aurelien@aurel32.net> X-Mailer: git-send-email 2.34.1 In-Reply-To: <20220124224857.3799610-1-aurelien@aurel32.net> References: <20220124224857.3799610-1-aurelien@aurel32.net> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Spam-Status: No, score=-13.3 required=5.0 tests=BAYES_00, DKIM_SIGNED, DKIM_VALID, DKIM_VALID_AU, DKIM_VALID_EF, GIT_PATCH_0, KAM_SHORT, SPF_HELO_PASS, SPF_NONE, TXREP autolearn=ham autolearn_force=no version=3.4.4 X-Spam-Checker-Version: SpamAssassin 3.4.4 (2020-01-24) on server2.sourceware.org X-BeenThere: libc-stable@sourceware.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Libc-stable mailing list List-Unsubscribe: , List-Archive: List-Help: List-Subscribe: , X-List-Received-Date: Mon, 24 Jan 2022 22:49:11 -0000 From: Siddhesh Poyarekar 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 Reviewed-by: Adhemerval Zanella Signed-off-by: Qualys Security Advisory Signed-off-by: Siddhesh Poyarekar (cherry picked from commit 23e0e8f5f1fb5ed150253d986ecccdc90c2dcd5e) --- NEWS | 7 + sysdeps/posix/getcwd.c | 7 + sysdeps/unix/sysv/linux/Makefile | 7 +- .../unix/sysv/linux/tst-getcwd-smallbuff.c | 241 ++++++++++++++++++ 4 files changed, 261 insertions(+), 1 deletion(-) create mode 100644 sysdeps/unix/sysv/linux/tst-getcwd-smallbuff.c diff --git a/NEWS b/NEWS index 5352599d7f..cc026f03b1 100644 --- a/NEWS +++ b/NEWS @@ -30,6 +30,12 @@ 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: [15271] dlfcn function failure after dlmopen terminates process @@ -50,6 +56,7 @@ The following bugs are resolved with this release: [28524] Conversion from ISO-2022-JP-3 with iconv may emit spurious NULs [28532] powerpc64[le]: CFI for assembly templated syscalls is incorrect [28768] CVE-2022-23218: Buffer overflow in sunrpc svcunix_create + [28769] CVE-2021-3999: Off-by-one buffer overflow/underflow in getcwd() [28770] CVE-2021-3998: Unexpected return value from realpath() for too long results Version 2.33 diff --git a/sysdeps/posix/getcwd.c b/sysdeps/posix/getcwd.c index f11644aae7..242e4dbe45 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 472eab700d..9531641f82 100644 --- a/sysdeps/unix/sysv/linux/Makefile +++ b/sysdeps/unix/sysv/linux/Makefile @@ -282,7 +282,12 @@ sysdep_routines += xstatconv internal_statvfs internal_statvfs64 \ 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 + . */ + +#include +#include +#include +#include +#include +#include +#include +#include +#include +#include +#include + +#include +#include +#include +#include +#include +#include + +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 -- 2.34.1