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glibc/stdlib/canonicalize.c
Siddhesh Poyarekar d084965adc realpath: Avoid overwriting preexisting error (CVE-2021-3998) 
Set errno and failure for paths that are too long only if no other error
occurred earlier.

Related: BZ #28770

Reviewed-by: Andreas Schwab <schwab@linux-m68k.org>
Signed-off-by: Siddhesh Poyarekar <siddhesh@sourceware.org>
(cherry picked from commit 84d2d0fe20)
2022-01-24 21:44:54 +05:30

476 lines
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/* Return the canonical absolute name of a given file.
Copyright (C) 1996-2021 Free Software Foundation, Inc.
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/>. */
#ifndef _LIBC
/* Don't use __attribute__ __nonnull__ in this compilation unit. Otherwise gcc
optimizes away the name == NULL test below. */
# define _GL_ARG_NONNULL(params)
# define _GL_USE_STDLIB_ALLOC 1
# include <libc-config.h>
#endif
/* Specification. */
#include <stdlib.h>
#include <errno.h>
#include <fcntl.h>
#include <limits.h>
#include <stdbool.h>
#include <string.h>
#include <sys/stat.h>
#include <unistd.h>
#include <eloop-threshold.h>
#include <filename.h>
#include <idx.h>
#include <intprops.h>
#include <scratch_buffer.h>
#ifdef _LIBC
# include <shlib-compat.h>
# define GCC_LINT 1
# define _GL_ATTRIBUTE_PURE __attribute__ ((__pure__))
#else
# define __canonicalize_file_name canonicalize_file_name
# define __realpath realpath
# include "pathmax.h"
# define __faccessat faccessat
# if defined _WIN32 && !defined __CYGWIN__
# define __getcwd _getcwd
# elif HAVE_GETCWD
# if IN_RELOCWRAPPER
/* When building the relocatable program wrapper, use the system's getcwd
function, not the gnulib override, otherwise we would get a link error.
*/
# undef getcwd
# endif
# if defined VMS && !defined getcwd
/* We want the directory in Unix syntax, not in VMS syntax.
The gnulib override of 'getcwd' takes 2 arguments; the original VMS
'getcwd' takes 3 arguments. */
# define __getcwd(buf, max) getcwd (buf, max, 0)
# else
# define __getcwd getcwd
# endif
# else
# define __getcwd(buf, max) getwd (buf)
# endif
# define __mempcpy mempcpy
# define __pathconf pathconf
# define __rawmemchr rawmemchr
# define __readlink readlink
# define __stat stat
#endif
/* Suppress bogus GCC -Wmaybe-uninitialized warnings. */
#if defined GCC_LINT || defined lint
# define IF_LINT(Code) Code
#else
# define IF_LINT(Code) /* empty */
#endif
#ifndef DOUBLE_SLASH_IS_DISTINCT_ROOT
# define DOUBLE_SLASH_IS_DISTINCT_ROOT false
#endif
#if defined _LIBC || !FUNC_REALPATH_WORKS
/* Return true if FILE's existence can be shown, false (setting errno)
otherwise. Follow symbolic links. */
static bool
file_accessible (char const *file)
{
# if defined _LIBC || HAVE_FACCESSAT
return __faccessat (AT_FDCWD, file, F_OK, AT_EACCESS) == 0;
# else
struct stat st;
return __stat (file, &st) == 0 || errno == EOVERFLOW;
# endif
}
/* True if concatenating END as a suffix to a file name means that the
code needs to check that the file name is that of a searchable
directory, since the canonicalize_filename_mode_stk code won't
check this later anyway when it checks an ordinary file name
component within END. END must either be empty, or start with a
slash. */
static bool _GL_ATTRIBUTE_PURE
suffix_requires_dir_check (char const *end)
{
/* If END does not start with a slash, the suffix is OK. */
while (ISSLASH (*end))
{
/* Two or more slashes act like a single slash. */
do
end++;
while (ISSLASH (*end));
switch (*end++)
{
default: return false; /* An ordinary file name component is OK. */
case '\0': return true; /* Trailing "/" is trouble. */
case '.': break; /* Possibly "." or "..". */
}
/* Trailing "/.", or "/.." even if not trailing, is trouble. */
if (!*end || (*end == '.' && (!end[1] || ISSLASH (end[1]))))
return true;
}
return false;
}
/* Append this to a file name to test whether it is a searchable directory.
On POSIX platforms "/" suffices, but "/./" is sometimes needed on
macOS 10.13 <https://bugs.gnu.org/30350>, and should also work on
platforms like AIX 7.2 that need at least "/.". */
#if defined _LIBC || defined LSTAT_FOLLOWS_SLASHED_SYMLINK
static char const dir_suffix[] = "/";
#else
static char const dir_suffix[] = "/./";
#endif
/* Return true if DIR is a searchable dir, false (setting errno) otherwise.
DIREND points to the NUL byte at the end of the DIR string.
Store garbage into DIREND[0 .. strlen (dir_suffix)]. */
static bool
dir_check (char *dir, char *dirend)
{
strcpy (dirend, dir_suffix);
return file_accessible (dir);
}
static idx_t
get_path_max (void)
{
# ifdef PATH_MAX
long int path_max = PATH_MAX;
# else
/* The caller invoked realpath with a null RESOLVED, even though
PATH_MAX is not defined as a constant. The glibc manual says
programs should not do this, and POSIX says the behavior is undefined.
Historically, glibc here used the result of pathconf, or 1024 if that
failed; stay consistent with this (dubious) historical practice. */
int err = errno;
long int path_max = __pathconf ("/", _PC_PATH_MAX);
__set_errno (err);
# endif
return path_max < 0 ? 1024 : path_max <= IDX_MAX ? path_max : IDX_MAX;
}
/* Act like __realpath (see below), with an additional argument
rname_buf that can be used as temporary storage.
If GCC_LINT is defined, do not inline this function with GCC 10.1
and later, to avoid creating a pointer to the stack that GCC
-Wreturn-local-addr incorrectly complains about. See:
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=93644
Although the noinline attribute can hurt performance a bit, no better way
to pacify GCC is known; even an explicit #pragma does not pacify GCC.
When the GCC bug is fixed this workaround should be limited to the
broken GCC versions. */
#if __GNUC_PREREQ (10, 1)
# if defined GCC_LINT || defined lint
__attribute__ ((__noinline__))
# elif __OPTIMIZE__ && !__NO_INLINE__
# define GCC_BOGUS_WRETURN_LOCAL_ADDR
# endif
#endif
static char *
realpath_stk (const char *name, char *resolved,
struct scratch_buffer *rname_buf)
{
char *dest;
char const *start;
char const *end;
int num_links = 0;
if (name == NULL)
{
/* As per Single Unix Specification V2 we must return an error if
either parameter is a null pointer. We extend this to allow
the RESOLVED parameter to be NULL in case the we are expected to
allocate the room for the return value. */
__set_errno (EINVAL);
return NULL;
}
if (name[0] == '\0')
{
/* As per Single Unix Specification V2 we must return an error if
the name argument points to an empty string. */
__set_errno (ENOENT);
return NULL;
}
struct scratch_buffer extra_buffer, link_buffer;
scratch_buffer_init (&extra_buffer);
scratch_buffer_init (&link_buffer);
scratch_buffer_init (rname_buf);
char *rname_on_stack = rname_buf->data;
char *rname = rname_on_stack;
bool end_in_extra_buffer = false;
bool failed = true;
/* This is always zero for Posix hosts, but can be 2 for MS-Windows
and MS-DOS X:/foo/bar file names. */
idx_t prefix_len = FILE_SYSTEM_PREFIX_LEN (name);
if (!IS_ABSOLUTE_FILE_NAME (name))
{
while (!__getcwd (rname, rname_buf->length))
{
if (errno != ERANGE)
{
dest = rname;
goto error;
}
if (!scratch_buffer_grow (rname_buf))
goto error_nomem;
rname = rname_buf->data;
}
dest = __rawmemchr (rname, '\0');
start = name;
prefix_len = FILE_SYSTEM_PREFIX_LEN (rname);
}
else
{
dest = __mempcpy (rname, name, prefix_len);
*dest++ = '/';
if (DOUBLE_SLASH_IS_DISTINCT_ROOT)
{
if (prefix_len == 0 /* implies ISSLASH (name[0]) */
&& ISSLASH (name[1]) && !ISSLASH (name[2]))
*dest++ = '/';
*dest = '\0';
}
start = name + prefix_len;
}
for ( ; *start; start = end)
{
/* Skip sequence of multiple file name separators. */
while (ISSLASH (*start))
++start;
/* Find end of component. */
for (end = start; *end && !ISSLASH (*end); ++end)
/* Nothing. */;
/* Length of this file name component; it can be zero if a file
name ends in '/'. */
idx_t startlen = end - start;
if (startlen == 0)
break;
else if (startlen == 1 && start[0] == '.')
/* nothing */;
else if (startlen == 2 && start[0] == '.' && start[1] == '.')
{
/* Back up to previous component, ignore if at root already. */
if (dest > rname + prefix_len + 1)
for (--dest; dest > rname && !ISSLASH (dest[-1]); --dest)
continue;
if (DOUBLE_SLASH_IS_DISTINCT_ROOT
&& dest == rname + 1 && !prefix_len
&& ISSLASH (*dest) && !ISSLASH (dest[1]))
dest++;
}
else
{
if (!ISSLASH (dest[-1]))
*dest++ = '/';
while (rname + rname_buf->length - dest
< startlen + sizeof dir_suffix)
{
idx_t dest_offset = dest - rname;
if (!scratch_buffer_grow_preserve (rname_buf))
goto error_nomem;
rname = rname_buf->data;
dest = rname + dest_offset;
}
dest = __mempcpy (dest, start, startlen);
*dest = '\0';
char *buf;
ssize_t n;
while (true)
{
buf = link_buffer.data;
idx_t bufsize = link_buffer.length;
n = __readlink (rname, buf, bufsize - 1);
if (n < bufsize - 1)
break;
if (!scratch_buffer_grow (&link_buffer))
goto error_nomem;
}
if (0 <= n)
{
if (++num_links > __eloop_threshold ())
{
__set_errno (ELOOP);
goto error;
}
buf[n] = '\0';
char *extra_buf = extra_buffer.data;
idx_t end_idx IF_LINT (= 0);
if (end_in_extra_buffer)
end_idx = end - extra_buf;
size_t len = strlen (end);
if (INT_ADD_OVERFLOW (len, n))
{
__set_errno (ENOMEM);
goto error_nomem;
}
while (extra_buffer.length <= len + n)
{
if (!scratch_buffer_grow_preserve (&extra_buffer))
goto error_nomem;
extra_buf = extra_buffer.data;
}
if (end_in_extra_buffer)
end = extra_buf + end_idx;
/* Careful here, end may be a pointer into extra_buf... */
memmove (&extra_buf[n], end, len + 1);
name = end = memcpy (extra_buf, buf, n);
end_in_extra_buffer = true;
if (IS_ABSOLUTE_FILE_NAME (buf))
{
idx_t pfxlen = FILE_SYSTEM_PREFIX_LEN (buf);
dest = __mempcpy (rname, buf, pfxlen);
*dest++ = '/'; /* It's an absolute symlink */
if (DOUBLE_SLASH_IS_DISTINCT_ROOT)
{
if (ISSLASH (buf[1]) && !ISSLASH (buf[2]) && !pfxlen)
*dest++ = '/';
*dest = '\0';
}
/* Install the new prefix to be in effect hereafter. */
prefix_len = pfxlen;
}
else
{
/* Back up to previous component, ignore if at root
already: */
if (dest > rname + prefix_len + 1)
for (--dest; dest > rname && !ISSLASH (dest[-1]); --dest)
continue;
if (DOUBLE_SLASH_IS_DISTINCT_ROOT && dest == rname + 1
&& ISSLASH (*dest) && !ISSLASH (dest[1]) && !prefix_len)
dest++;
}
}
else if (! (suffix_requires_dir_check (end)
? dir_check (rname, dest)
: errno == EINVAL))
goto error;
}
}
if (dest > rname + prefix_len + 1 && ISSLASH (dest[-1]))
--dest;
if (DOUBLE_SLASH_IS_DISTINCT_ROOT && dest == rname + 1 && !prefix_len
&& ISSLASH (*dest) && !ISSLASH (dest[1]))
dest++;
failed = false;
error:
*dest++ = '\0';
if (resolved != NULL)
{
if (dest - rname <= get_path_max ())
rname = strcpy (resolved, rname);
else if (!failed)
{
failed = true;
__set_errno (ENAMETOOLONG);
}
}
error_nomem:
scratch_buffer_free (&extra_buffer);
scratch_buffer_free (&link_buffer);
if (failed || rname == resolved)
{
scratch_buffer_free (rname_buf);
return failed ? NULL : resolved;
}
return scratch_buffer_dupfree (rname_buf, dest - rname);
}
/* Return the canonical absolute name of file NAME. A canonical name
does not contain any ".", ".." components nor any repeated file name
separators ('/') or symlinks. All file name components must exist. If
RESOLVED is null, the result is malloc'd; otherwise, if the
canonical name is PATH_MAX chars or more, returns null with 'errno'
set to ENAMETOOLONG; if the name fits in fewer than PATH_MAX chars,
returns the name in RESOLVED. If the name cannot be resolved and
RESOLVED is non-NULL, it contains the name of the first component
that cannot be resolved. If the name can be resolved, RESOLVED
holds the same value as the value returned. */
char *
__realpath (const char *name, char *resolved)
{
#ifdef GCC_BOGUS_WRETURN_LOCAL_ADDR
#warning "GCC might issue a bogus -Wreturn-local-addr warning here."
#warning "See <https://gcc.gnu.org/bugzilla/show_bug.cgi?id=93644>."
#endif
struct scratch_buffer rname_buffer;
return realpath_stk (name, resolved, &rname_buffer);
}
libc_hidden_def (__realpath)
versioned_symbol (libc, __realpath, realpath, GLIBC_2_3);
#endif /* !FUNC_REALPATH_WORKS || defined _LIBC */
#if SHLIB_COMPAT(libc, GLIBC_2_0, GLIBC_2_3)
char *
attribute_compat_text_section
__old_realpath (const char *name, char *resolved)
{
if (resolved == NULL)
{
__set_errno (EINVAL);
return NULL;
}
return __realpath (name, resolved);
}
compat_symbol (libc, __old_realpath, realpath, GLIBC_2_0);
#endif
char *
__canonicalize_file_name (const char *name)
{
return __realpath (name, NULL);
}
weak_alias (__canonicalize_file_name, canonicalize_file_name)
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