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/*
* realpath.c -- canonicalize pathname by removing symlinks
* Copyright (C) 1993 Rick Sladkey <jrs@world.std.com>
*
* This program is free software; you can redistribute it and/or modify
* it under the terms of the GNU Library Public License as published by
* the Free Software Foundation; either version 2, 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 Library Public License for more details.
*/
/*
* This routine is part of libc. We include it nevertheless,
* since the libc version has some security flaws.
*/
#include <limits.h> /* for PATH_MAX */
#include <unistd.h>
#include <string.h>
#include <errno.h>
#include "realpath.h"
#include "sundries.h" /* for xstrdup */
#define MAX_READLINKS 32
char *
myrealpath(const char *path, char *resolved_path, int maxreslth) {
char *npath;
char link_path[PATH_MAX+1];
int readlinks = 0;
int n;
npath = resolved_path;
/* If it's a relative pathname use getcwd for starters. */
if (*path != '/') {
getcwd(npath, maxreslth-2);
npath += strlen(npath);
if (npath[-1] != '/')
*npath++ = '/';
} else {
*npath++ = '/';
path++;
}
/* Expand each slash-separated pathname component. */
while (*path != '\0') {
/* Ignore stray "/" */
if (*path == '/') {
path++;
continue;
}
if (*path == '.' && (path[1] == '\0' || path[1] == '/')) {
/* Ignore "." */
path++;
continue;
}
if (*path == '.' && path[1] == '.' &&
(path[2] == '\0' || path[2] == '/')) {
/* Backup for ".." */
path += 2;
while (npath > resolved_path+1 &&
(--npath)[-1] != '/')
;
continue;
}
/* Safely copy the next pathname component. */
while (*path != '\0' && *path != '/') {
if (npath-resolved_path > maxreslth-2) {
errno = ENAMETOOLONG;
return NULL;
}
*npath++ = *path++;
}
/* Protect against infinite loops. */
if (readlinks++ > MAX_READLINKS) {
errno = ELOOP;
return NULL;
}
/* See if latest pathname component is a symlink. */
*npath = '\0';
n = readlink(resolved_path, link_path, PATH_MAX);
if (n < 0) {
/* EINVAL means the file exists but isn't a symlink. */
if (errno != EINVAL)
return NULL;
} else {
/* Note: readlink doesn't add the null byte. */
link_path[n] = '\0';
if (*link_path == '/')
/* Start over for an absolute symlink. */
npath = resolved_path;
else
/* Otherwise back up over this component. */
while (*(--npath) != '/')
;
/* Safe sex check. */
if (strlen(path) + n >= sizeof(link_path)) {
errno = ENAMETOOLONG;
return NULL;
}
/* Insert symlink contents into path. */
strcat(link_path, path);
path = xstrdup(link_path);
}
*npath++ = '/';
}
/* Delete trailing slash but don't whomp a lone slash. */
if (npath != resolved_path+1 && npath[-1] == '/')
npath--;
/* Make sure it's null terminated. */
*npath = '\0';
return resolved_path;
}
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