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wget/lib/canonicalize.c

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/* Return the canonical absolute name of a given file.
Copyright (C) 1996-2023 Free Software Foundation, Inc.
This program is free software: you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation, either version 3 of the License, or
(at your option) any later version.
This program 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 General Public License for more details.
You should have received a copy of the GNU General Public License
along with this program. If not, see <https://www.gnu.org/licenses/>. */
#include <config.h>
#include "canonicalize.h"
#include <errno.h>
#include <fcntl.h>
#include <string.h>
#include <sys/stat.h>
#include <unistd.h>
#include <filename.h>
#include <idx.h>
#include <intprops.h>
#include <scratch_buffer.h>
#include "attribute.h"
#include "file-set.h"
#include "hash-triple.h"
#include "xalloc.h"
/* 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 ISSLASH ('\\')
# define SLASHES "/\\"
#else
# define SLASHES "/"
#endif
/* Return true if FILE's existence can be shown, false (setting errno)
otherwise. Follow symbolic links. */
static bool
file_accessible (char const *file)
{
# if 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 "/.". */
#ifdef 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);
}
#if !((HAVE_CANONICALIZE_FILE_NAME && FUNC_REALPATH_WORKS) \
|| GNULIB_CANONICALIZE_LGPL)
/* 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 components must exist.
The result is malloc'd. */
char *
canonicalize_file_name (const char *name)
{
return canonicalize_filename_mode (name, CAN_EXISTING);
}
#endif /* !HAVE_CANONICALIZE_FILE_NAME */
static bool
multiple_bits_set (canonicalize_mode_t i)
{
return (i & (i - 1)) != 0;
}
/* Return true if we've already seen the triple, <FILENAME, dev, ino>.
If *HT is not initialized, initialize it. */
static bool
seen_triple (Hash_table **ht, char const *filename, struct stat const *st)
{
if (*ht == NULL)
{
idx_t initial_capacity = 7;
*ht = hash_initialize (initial_capacity,
NULL,
triple_hash,
triple_compare_ino_str,
triple_free);
if (*ht == NULL)
xalloc_die ();
}
if (seen_file (*ht, filename, st))
return true;
record_file (*ht, filename, st);
return false;
}
/* Scratch buffers used by canonicalize_filename_mode_stk and managed
by __realpath. */
struct realpath_bufs
{
struct scratch_buffer rname;
struct scratch_buffer extra;
struct scratch_buffer link;
};
static char *
canonicalize_filename_mode_stk (const char *name, canonicalize_mode_t can_mode,
struct realpath_bufs *bufs)
{
char *dest;
char const *start;
char const *end;
Hash_table *ht = NULL;
bool logical = (can_mode & CAN_NOLINKS) != 0;
int num_links = 0;
canonicalize_mode_t can_exist = can_mode & CAN_MODE_MASK;
if (multiple_bits_set (can_exist))
{
errno = EINVAL;
return NULL;
}
if (name == NULL)
{
errno = EINVAL;
return NULL;
}
if (name[0] == '\0')
{
errno = ENOENT;
return NULL;
}
char *rname = bufs->rname.data;
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 (bufs->rname.data, bufs->rname.length))
{
switch (errno)
{
case ERANGE:
if (scratch_buffer_grow (&bufs->rname))
break;
FALLTHROUGH;
case ENOMEM:
xalloc_die ();
default:
dest = rname;
goto error;
}
rname = bufs->rname.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++ = '/';
#if defined _WIN32 && !defined __CYGWIN__
/* For UNC file names '\\server\path\to\file', extend the prefix
to include the server: '\\server\'. */
{
idx_t i;
for (i = 2; name[i] != '\0' && !ISSLASH (name[i]); )
i++;
if (name[i] != '\0' /* implies ISSLASH (name[i]) */
&& i + 1 < bufs->rname.length)
{
prefix_len = i;
memcpy (dest, name + 2, i - 2 + 1);
dest += i - 2 + 1;
}
else
{
/* Either name = '\\server'; this is an invalid file name.
Or name = '\\server\...' and server is more than
bufs->rname.length - 4 bytes long. In either
case, stop the UNC processing. */
}
}
#endif
}
*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 + bufs->rname.length - dest
< startlen + sizeof dir_suffix)
{
idx_t dest_offset = dest - rname;
if (!scratch_buffer_grow_preserve (&bufs->rname))
xalloc_die ();
rname = bufs->rname.data;
dest = rname + dest_offset;
}
dest = mempcpy (dest, start, startlen);
*dest = '\0';
char *buf;
ssize_t n = -1;
if (!logical)
{
while (true)
{
buf = bufs->link.data;
idx_t bufsize = bufs->link.length;
n = readlink (rname, buf, bufsize - 1);
if (n < bufsize - 1)
break;
if (!scratch_buffer_grow (&bufs->link))
xalloc_die ();
}
}
if (0 <= n)
{
/* A physical traversal and RNAME is a symbolic link. */
if (num_links < 20)
num_links++;
else if (*start)
{
/* Enough symlinks have been seen that it is time to
worry about being in a symlink cycle.
Get the device and inode of the parent directory, as
pre-2017 POSIX says this info is not reliable for
symlinks. */
struct stat st;
dest[- startlen] = '\0';
if (stat (*rname ? rname : ".", &st) != 0)
goto error;
dest[- startlen] = *start;
/* Detect loops. We cannot use the cycle-check module here,
since it's possible to encounter the same parent
directory more than once in a given traversal. However,
encountering the same (parentdir, START) pair twice does
indicate a loop. */
if (seen_triple (&ht, start, &st))
{
if (can_exist == CAN_MISSING)
continue;
errno = ELOOP;
goto error;
}
}
buf[n] = '\0';
char *extra_buf = bufs->extra.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))
xalloc_die ();
while (bufs->extra.length <= len + n)
{
if (!scratch_buffer_grow_preserve (&bufs->extra))
xalloc_die ();
extra_buf = bufs->extra.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 (! (can_exist == CAN_MISSING
|| (suffix_requires_dir_check (end)
? dir_check (rname, dest)
: !logical
? errno == EINVAL
: *end || file_accessible (rname))
|| (can_exist == CAN_ALL_BUT_LAST
&& errno == ENOENT
&& !end[strspn (end, SLASHES)])))
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:
if (ht)
hash_free (ht);
if (failed)
return NULL;
*dest++ = '\0';
char *result = malloc (dest - rname);
if (!result)
xalloc_die ();
return memcpy (result, rname, dest - rname);
}
/* Return the canonical absolute name of file NAME, while treating
missing elements according to CAN_MODE. A canonical name
does not contain any ".", ".." components nor any repeated file name
separators ('/') or, depending on other CAN_MODE flags, symlinks.
Whether components must exist or not depends on canonicalize mode.
The result is malloc'd. */
char *
canonicalize_filename_mode (const char *name, canonicalize_mode_t can_mode)
{
struct realpath_bufs bufs;
scratch_buffer_init (&bufs.rname);
scratch_buffer_init (&bufs.extra);
scratch_buffer_init (&bufs.link);
char *result = canonicalize_filename_mode_stk (name, can_mode, &bufs);
scratch_buffer_free (&bufs.link);
scratch_buffer_free (&bufs.extra);
scratch_buffer_free (&bufs.rname);
return result;
}
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