sudo/lib/util/realpath.c

/*
 * Copyright (c) 1989, 1991, 1993, 1995
 *	The Regents of the University of California.  All rights reserved.
 *
 * This code is derived from software contributed to Berkeley by
 * Jan-Simon Pendry.
 *
 * 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. Neither the name of the University nor the names of its contributors
 *    may be used to endorse or promote products derived from this software
 *    without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE REGENTS 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 REGENTS 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.
 *
 *	@(#)getcwd.c	8.5 (Berkeley) 2/7/95
 */

#include <config.h>

#ifndef HAVE_REALPATH

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

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

/*
 * char *realpath(const char *path, char *resolved);
 *
 * 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 *
sudo_realpath(const char * restrict path, char * restrict resolved)
{
	struct stat sb;
	int idx = 0, nlnk = 0;
	const char *q;
	char *p, wbuf[2][PATH_MAX], *fres = NULL;
	static long symloop_max;
	size_t len;
	ssize_t n;

	if (path == NULL) {
		errno = EINVAL;
		return NULL;
	}

	if (symloop_max == 0) {
	    if ((symloop_max = sysconf(_SC_SYMLOOP_MAX)) <= 0)
		symloop_max = 8;	/* POSIX */
	}

	if (resolved == NULL) {
		fres = resolved = malloc(PATH_MAX);
		if (resolved == NULL)
			return NULL;
	}


	/*
	 * Build real path one by one with paying an attention to .,
	 * .. and symbolic link.
	 */

	/*
	 * `p' is where we'll put a new component with prepending
	 * a delimiter.
	 */
	p = resolved;

	if (*path == '\0') {
		*p = '\0';
		errno = ENOENT;
		goto out;
	}

	/* If relative path, start from current working directory. */
	if (*path != '/') {
		if (getcwd(resolved, PATH_MAX) == NULL) {
			p[0] = '.';
			p[1] = '\0';
			goto out;
		}
		len = strlen(resolved);
		if (len > 1)
			p += len;
	}

loop:
	/* Skip any slash. */
	while (*path == '/')
		path++;

	if (*path == '\0') {
		if (p == resolved)
			*p++ = '/';
		*p = '\0';
		return resolved;
	}

	/* Find the end of this component. */
	q = path;
	do {
		q++;
	} while (*q != '/' && *q != '\0');

	/* Test . or .. */
	if (path[0] == '.') {
		if (q - path == 1) {
			path = q;
			goto loop;
		}
		if (path[1] == '.' && q - path == 2) {
			/* Trim the last component. */
			if (p != resolved)
				while (*--p != '/')
					continue;
			path = q;
			goto loop;
		}
	}

	/* Append this component. */
	if (p - resolved + 1 + q - path + 1 > PATH_MAX) {
		errno = ENAMETOOLONG;
		if (p == resolved)
			*p++ = '/';
		*p = '\0';
		goto out;
	}
	p[0] = '/';
	memcpy(&p[1], path, (size_t)(q - path));
	p[1 + q - path] = '\0';

	/*
	 * If this component is a symlink, toss it and prepend link
	 * target to unresolved path.
	 */
	if (lstat(resolved, &sb) == -1)
		goto out;

	if (S_ISLNK(sb.st_mode)) {
		if (nlnk++ >= symloop_max) {
			errno = ELOOP;
			goto out;
		}
		n = readlink(resolved, wbuf[idx], sizeof(wbuf[0]) - 1);
		if (n < 0)
			goto out;
		if (n == 0) {
			errno = ENOENT;
			goto out;
		}

		/* Append unresolved path to link target and switch to it. */
		if ((size_t)n + (len = strlen(q)) + 1 > sizeof(wbuf[0])) {
			errno = ENAMETOOLONG;
			goto out;
		}
		memcpy(&wbuf[idx][n], q, len + 1);
		path = wbuf[idx];
		idx ^= 1;

		/* If absolute symlink, start from root. */
		if (*path == '/')
			p = resolved;
		goto loop;
	}
	if (*q == '/' && !S_ISDIR(sb.st_mode)) {
		errno = ENOTDIR;
		goto out;
	}

	/* Advance both resolved and unresolved path. */
	p += 1 + q - path;
	path = q;
	goto loop;
out:
	free(fres);
	return NULL;
}
#endif /* HAVE_REALPATH */