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