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52a713fdd0
Currently getcwd(3) can succeed without returning an absolute path because the underlying getcwd syscall, starting with linux commit v2.6.36-rc1~96^2~2, may succeed without returning an absolute path. This is a conformance issue because "The getcwd() function shall place an absolute pathname of the current working directory in the array pointed to by buf, and return buf". This is also a security issue because a non-absolute path returned by getcwd(3) causes a buffer underflow in realpath(3). Fix this by checking the path returned by getcwd syscall and falling back to generic_getcwd if the path is not absolute, effectively making getcwd(3) fail with ENOENT. The error code is chosen for consistency with the case when the current directory is unlinked. [BZ #22679] CVE-2018-1000001 * sysdeps/unix/sysv/linux/getcwd.c (__getcwd): Fall back to generic_getcwd if the path returned by getcwd syscall is not absolute. * io/tst-getcwd-abspath.c: New test. * io/Makefile (tests): Add tst-getcwd-abspath.
136 lines
3.5 KiB
C
136 lines
3.5 KiB
C
/* Determine current working directory. Linux version.
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Copyright (C) 1997-2018 Free Software Foundation, Inc.
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This file is part of the GNU C Library.
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Contributed by Ulrich Drepper <drepper@cygnus.com>, 1997.
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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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<http://www.gnu.org/licenses/>. */
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#include <assert.h>
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#include <errno.h>
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#include <limits.h>
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#include <stdlib.h>
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#include <unistd.h>
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#include <sys/param.h>
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#include <sysdep.h>
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#include <sys/syscall.h>
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/* If we compile the file for use in ld.so we don't need the feature
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that getcwd() allocates the buffers itself. */
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#if IS_IN (rtld)
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# define NO_ALLOCATION 1
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#endif
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/* The "proc" filesystem provides an easy method to retrieve the value.
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For each process, the corresponding directory contains a symbolic link
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named `cwd'. Reading the content of this link immediate gives us the
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information. But we have to take care for systems which do not have
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the proc filesystem mounted. Use the POSIX implementation in this case. */
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static char *generic_getcwd (char *buf, size_t size);
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char *
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__getcwd (char *buf, size_t size)
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{
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char *path;
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char *result;
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#ifndef NO_ALLOCATION
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size_t alloc_size = size;
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if (size == 0)
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{
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if (buf != NULL)
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{
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__set_errno (EINVAL);
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return NULL;
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}
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alloc_size = MAX (PATH_MAX, __getpagesize ());
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}
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if (buf == NULL)
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{
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path = malloc (alloc_size);
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if (path == NULL)
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return NULL;
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}
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else
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#else
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# define alloc_size size
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#endif
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path = buf;
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int retval;
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retval = INLINE_SYSCALL (getcwd, 2, path, alloc_size);
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if (retval > 0 && path[0] == '/')
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{
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#ifndef NO_ALLOCATION
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if (buf == NULL && size == 0)
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/* Ensure that the buffer is only as large as necessary. */
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buf = realloc (path, (size_t) retval);
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if (buf == NULL)
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/* Either buf was NULL all along, or `realloc' failed but
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we still have the original string. */
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buf = path;
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#endif
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return buf;
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}
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/* The system call either cannot handle paths longer than a page
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or can succeed without returning an absolute path. Just use the
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generic implementation right away. */
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if (retval >= 0 || errno == ENAMETOOLONG)
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{
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#ifndef NO_ALLOCATION
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if (buf == NULL && size == 0)
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{
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free (path);
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path = NULL;
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}
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#endif
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result = generic_getcwd (path, size);
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#ifndef NO_ALLOCATION
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if (result == NULL && buf == NULL && size != 0)
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free (path);
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#endif
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return result;
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}
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/* It should never happen that the `getcwd' syscall failed because
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the buffer is too small if we allocated the buffer ourselves
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large enough. */
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assert (errno != ERANGE || buf != NULL || size != 0);
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#ifndef NO_ALLOCATION
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if (buf == NULL)
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free (path);
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#endif
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return NULL;
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}
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weak_alias (__getcwd, getcwd)
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/* Get the code for the generic version. */
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#define GETCWD_RETURN_TYPE static char *
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#define __getcwd generic_getcwd
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#include <sysdeps/posix/getcwd.c>
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