realpath.c revision 236582
1/*
2 * Copyright (c) 2003 Constantin S. Svintsoff <kostik@iclub.nsu.ru>
3 *
4 * Redistribution and use in source and binary forms, with or without
5 * modification, are permitted provided that the following conditions
6 * are met:
7 * 1. Redistributions of source code must retain the above copyright
8 *    notice, this list of conditions and the following disclaimer.
9 * 2. Redistributions in binary form must reproduce the above copyright
10 *    notice, this list of conditions and the following disclaimer in the
11 *    documentation and/or other materials provided with the distribution.
12 * 3. The names of the authors may not be used to endorse or promote
13 *    products derived from this software without specific prior written
14 *    permission.
15 *
16 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
17 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
18 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
19 * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
20 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
21 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
22 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
23 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
24 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
25 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
26 * SUCH DAMAGE.
27 */
28
29#if defined(LIBC_SCCS) && !defined(lint)
30static char sccsid[] = "@(#)realpath.c	8.1 (Berkeley) 2/16/94";
31#endif /* LIBC_SCCS and not lint */
32#include <sys/cdefs.h>
33__FBSDID("$FreeBSD: head/lib/libc/stdlib/realpath.c 236582 2012-06-04 21:34:49Z ache $");
34
35#include "namespace.h"
36#include <sys/param.h>
37#include <sys/stat.h>
38
39#include <errno.h>
40#include <stdlib.h>
41#include <string.h>
42#include <unistd.h>
43#include "un-namespace.h"
44
45/*
46 * Find the real name of path, by removing all ".", ".." and symlink
47 * components.  Returns (resolved) on success, or (NULL) on failure,
48 * in which case the path which caused trouble is left in (resolved).
49 */
50char *
51realpath(const char * __restrict path, char * __restrict resolved)
52{
53	struct stat sb;
54	char *p, *q, *s;
55	size_t left_len, resolved_len;
56	unsigned symlinks;
57	int m, serrno, slen;
58	char left[PATH_MAX], next_token[PATH_MAX], symlink[PATH_MAX];
59
60	if (path == NULL) {
61		errno = EINVAL;
62		return (NULL);
63	}
64	if (path[0] == '\0') {
65		errno = ENOENT;
66		return (NULL);
67	}
68	if (resolved == NULL) {
69		resolved = malloc(PATH_MAX);
70		if (resolved == NULL)
71			return (NULL);
72		m = 1;
73	} else
74		m = 0;
75	symlinks = 0;
76	if (path[0] == '/') {
77		resolved[0] = '/';
78		resolved[1] = '\0';
79		if (path[1] == '\0')
80			return (resolved);
81		resolved_len = 1;
82		left_len = strlcpy(left, path + 1, sizeof(left));
83	} else {
84		if (getcwd(resolved, PATH_MAX) == NULL) {
85			if (m) {
86				serrno = errno;
87				free(resolved);
88				errno = serrno;
89			} else {
90				resolved[0] = '.';
91				resolved[1] = '\0';
92			}
93			return (NULL);
94		}
95		resolved_len = strlen(resolved);
96		left_len = strlcpy(left, path, sizeof(left));
97	}
98	if (left_len >= sizeof(left) || resolved_len >= PATH_MAX) {
99		if (m)
100			free(resolved);
101		errno = ENAMETOOLONG;
102		return (NULL);
103	}
104
105	/*
106	 * Iterate over path components in `left'.
107	 */
108	while (left_len != 0) {
109		/*
110		 * Extract the next path component and adjust `left'
111		 * and its length.
112		 */
113		p = strchr(left, '/');
114		s = p ? p : left + left_len;
115		if (s - left >= sizeof(next_token)) {
116			if (m)
117				free(resolved);
118			errno = ENAMETOOLONG;
119			return (NULL);
120		}
121		memcpy(next_token, left, s - left);
122		next_token[s - left] = '\0';
123		left_len -= s - left;
124		if (p != NULL)
125			memmove(left, s + 1, left_len + 1);
126		if (resolved[resolved_len - 1] != '/') {
127			if (resolved_len + 1 >= PATH_MAX) {
128				if (m)
129					free(resolved);
130				errno = ENAMETOOLONG;
131				return (NULL);
132			}
133			resolved[resolved_len++] = '/';
134			resolved[resolved_len] = '\0';
135		}
136		if (next_token[0] == '\0') {
137			/*
138			 * Handle consequential slashes.  The path
139			 * before slash shall point to a directory.
140			 *
141			 * Only the trailing slashes are not covered
142			 * by other checks in the loop, but we verify
143			 * the prefix for any (rare) "//" or "/\0"
144			 * occurence to not implement lookahead.
145			 */
146			if (lstat(resolved, &sb) != 0) {
147				if (m) {
148					serrno = errno;
149					free(resolved);
150					errno = serrno;
151				}
152				return (NULL);
153			}
154			if (!S_ISDIR(sb.st_mode)) {
155				if (m)
156					free(resolved);
157				errno = ENOTDIR;
158				return (NULL);
159			}
160			continue;
161		}
162		else if (strcmp(next_token, ".") == 0)
163			continue;
164		else if (strcmp(next_token, "..") == 0) {
165			/*
166			 * Strip the last path component except when we have
167			 * single "/"
168			 */
169			if (resolved_len > 1) {
170				resolved[resolved_len - 1] = '\0';
171				q = strrchr(resolved, '/') + 1;
172				*q = '\0';
173				resolved_len = q - resolved;
174			}
175			continue;
176		}
177
178		/*
179		 * Append the next path component and lstat() it.
180		 */
181		resolved_len = strlcat(resolved, next_token, PATH_MAX);
182		if (resolved_len >= PATH_MAX) {
183			if (m)
184				free(resolved);
185			errno = ENAMETOOLONG;
186			return (NULL);
187		}
188		if (lstat(resolved, &sb) != 0) {
189			if (errno != ENOENT || p != NULL)
190				errno = ENOTDIR;
191			if (m) {
192				serrno = errno;
193				free(resolved);
194				errno = serrno;
195			}
196			return (NULL);
197		}
198		if (S_ISLNK(sb.st_mode)) {
199			if (symlinks++ > MAXSYMLINKS) {
200				if (m)
201					free(resolved);
202				errno = ELOOP;
203				return (NULL);
204			}
205			slen = readlink(resolved, symlink, sizeof(symlink) - 1);
206			if (slen < 0) {
207				if (m) {
208					serrno = errno;
209					free(resolved);
210					errno = serrno;
211				}
212				return (NULL);
213			}
214			symlink[slen] = '\0';
215			if (symlink[0] == '/') {
216				resolved[1] = 0;
217				resolved_len = 1;
218			} else if (resolved_len > 1) {
219				/* Strip the last path component. */
220				resolved[resolved_len - 1] = '\0';
221				q = strrchr(resolved, '/') + 1;
222				*q = '\0';
223				resolved_len = q - resolved;
224			}
225
226			/*
227			 * If there are any path components left, then
228			 * append them to symlink. The result is placed
229			 * in `left'.
230			 */
231			if (p != NULL) {
232				if (symlink[slen - 1] != '/') {
233					if (slen + 1 >= sizeof(symlink)) {
234						if (m)
235							free(resolved);
236						errno = ENAMETOOLONG;
237						return (NULL);
238					}
239					symlink[slen] = '/';
240					symlink[slen + 1] = 0;
241				}
242				left_len = strlcat(symlink, left,
243				    sizeof(symlink));
244				if (left_len >= sizeof(left)) {
245					if (m)
246						free(resolved);
247					errno = ENAMETOOLONG;
248					return (NULL);
249				}
250			}
251			left_len = strlcpy(left, symlink, sizeof(left));
252		}
253	}
254
255	/*
256	 * Remove trailing slash except when the resolved pathname
257	 * is a single "/".
258	 */
259	if (resolved_len > 1 && resolved[resolved_len - 1] == '/')
260		resolved[resolved_len - 1] = '\0';
261	return (resolved);
262}
263