/*      $OpenBSD: sftp-realpath.c,v 1.2 2021/09/02 21:03:54 deraadt Exp $ */
/*
 * Copyright (c) 2003 Constantin S. Svintsoff <kostik@iclub.nsu.ru>
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 * 3. The names of the authors may not be used to endorse or promote
 *    products derived from this software without specific prior written
 *    permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 */

#include "includes.h"

#include <sys/types.h>
#include <sys/stat.h>

#include <errno.h>
#include <stdlib.h>
#include <stddef.h>
#include <string.h>
#include <unistd.h>
#include <limits.h>

#ifndef SYMLOOP_MAX
# define SYMLOOP_MAX 32
#endif

/* XXX rewrite sftp-server to use POSIX realpath and remove this hack */

char *sftp_realpath(const char *path, char *resolved);

/*
 * char *realpath(const char *path, char resolved[PATH_MAX]);
 *
 * Find the real name of path, by removing all ".", ".." and symlink
 * components.  Returns (resolved) on success, or (NULL) on failure,
 * in which case the path which caused trouble is left in (resolved).
 */
char *
sftp_realpath(const char *path, char *resolved)
{
        struct stat sb;
        char *p, *q, *s;
        size_t left_len, resolved_len;
        unsigned symlinks;
        int serrno, slen, mem_allocated;
        char left[PATH_MAX], next_token[PATH_MAX], symlink[PATH_MAX];

        if (path[0] == '\0') {
                errno = ENOENT;
                return (NULL);
        }

        serrno = errno;

        if (resolved == NULL) {
                resolved = malloc(PATH_MAX);
                if (resolved == NULL)
                        return (NULL);
                mem_allocated = 1;
        } else
                mem_allocated = 0;

        symlinks = 0;
        if (path[0] == '/') {
                resolved[0] = '/';
                resolved[1] = '\0';
                if (path[1] == '\0')
                        return (resolved);
                resolved_len = 1;
                left_len = strlcpy(left, path + 1, sizeof(left));
        } else {
                if (getcwd(resolved, PATH_MAX) == NULL) {
                        if (mem_allocated)
                                free(resolved);
                        else
                                strlcpy(resolved, ".", PATH_MAX);
                        return (NULL);
                }
                resolved_len = strlen(resolved);
                left_len = strlcpy(left, path, sizeof(left));
        }
        if (left_len >= sizeof(left) || resolved_len >= PATH_MAX) {
                errno = ENAMETOOLONG;
                goto err;
        }

        /*
         * Iterate over path components in `left'.
         */
        while (left_len != 0) {
                /*
                 * Extract the next path component and adjust `left'
                 * and its length.
                 */
                p = strchr(left, '/');
                s = p ? p : left + left_len;
                if (s - left >= (ptrdiff_t)sizeof(next_token)) {
                        errno = ENAMETOOLONG;
                        goto err;
                }
                memcpy(next_token, left, s - left);
                next_token[s - left] = '\0';
                left_len -= s - left;
                if (p != NULL)
                        memmove(left, s + 1, left_len + 1);
                if (resolved[resolved_len - 1] != '/') {
                        if (resolved_len + 1 >= PATH_MAX) {
                                errno = ENAMETOOLONG;
                                goto err;
                        }
                        resolved[resolved_len++] = '/';
                        resolved[resolved_len] = '\0';
                }
                if (next_token[0] == '\0')
                        continue;
                else if (strcmp(next_token, ".") == 0)
                        continue;
                else if (strcmp(next_token, "..") == 0) {
                        /*
                         * Strip the last path component except when we have
                         * single "/"
                         */
                        if (resolved_len > 1) {
                                resolved[resolved_len - 1] = '\0';
                                q = strrchr(resolved, '/') + 1;
                                *q = '\0';
                                resolved_len = q - resolved;
                        }
                        continue;
                }

                /*
                 * Append the next path component and lstat() it. If
                 * lstat() fails we still can return successfully if
                 * there are no more path components left.
                 */
                resolved_len = strlcat(resolved, next_token, PATH_MAX);
                if (resolved_len >= PATH_MAX) {
                        errno = ENAMETOOLONG;
                        goto err;
                }
                if (lstat(resolved, &sb) != 0) {
                        if (errno == ENOENT && p == NULL) {
                                errno = serrno;
                                return (resolved);
                        }
                        goto err;
                }
                if (S_ISLNK(sb.st_mode)) {
                        if (symlinks++ > SYMLOOP_MAX) {
                                errno = ELOOP;
                                goto err;
                        }
                        slen = readlink(resolved, symlink, sizeof(symlink) - 1);
                        if (slen < 0)
                                goto err;
                        symlink[slen] = '\0';
                        if (symlink[0] == '/') {
                                resolved[1] = 0;
                                resolved_len = 1;
                        } else if (resolved_len > 1) {
                                /* Strip the last path component. */
                                resolved[resolved_len - 1] = '\0';
                                q = strrchr(resolved, '/') + 1;
                                *q = '\0';
                                resolved_len = q - resolved;
                        }

                        /*
                         * If there are any path components left, then
                         * append them to symlink. The result is placed
                         * in `left'.
                         */
                        if (p != NULL) {
                                if (symlink[slen - 1] != '/') {
                                        if (slen + 1 >=
                                            (ptrdiff_t)sizeof(symlink)) {
                                                errno = ENAMETOOLONG;
                                                goto err;
                                        }
                                        symlink[slen] = '/';
                                        symlink[slen + 1] = 0;
                                }
                                left_len = strlcat(symlink, left, sizeof(symlink));
                                if (left_len >= sizeof(symlink)) {
                                        errno = ENAMETOOLONG;
                                        goto err;
                                }
                        }
                        left_len = strlcpy(left, symlink, sizeof(left));
                }
        }

        /*
         * Remove trailing slash except when the resolved pathname
         * is a single "/".
         */
        if (resolved_len > 1 && resolved[resolved_len - 1] == '/')
                resolved[resolved_len - 1] = '\0';
        return (resolved);

err:
        if (mem_allocated)
                free(resolved);
        return (NULL);
}