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)
30 static 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: stable/10/lib/libc/stdlib/realpath.c 319131 2017-05-29 13:00:39Z kib $");
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  */
50 static char *
realpath1(const char * path,char * resolved)51 realpath1(const char *path, char *resolved)
52 {
53 	struct stat sb;
54 	char *p, *q;
55 	size_t left_len, resolved_len, next_token_len;
56 	unsigned symlinks;
57 	ssize_t slen;
58 	char left[PATH_MAX], next_token[PATH_MAX], symlink[PATH_MAX];
59 
60 	symlinks = 0;
61 	if (path[0] == '/') {
62 		resolved[0] = '/';
63 		resolved[1] = '\0';
64 		if (path[1] == '\0')
65 			return (resolved);
66 		resolved_len = 1;
67 		left_len = strlcpy(left, path + 1, sizeof(left));
68 	} else {
69 		if (getcwd(resolved, PATH_MAX) == NULL) {
70 			resolved[0] = '.';
71 			resolved[1] = '\0';
72 			return (NULL);
73 		}
74 		resolved_len = strlen(resolved);
75 		left_len = strlcpy(left, path, sizeof(left));
76 	}
77 	if (left_len >= sizeof(left) || resolved_len >= PATH_MAX) {
78 		errno = ENAMETOOLONG;
79 		return (NULL);
80 	}
81 
82 	/*
83 	 * Iterate over path components in `left'.
84 	 */
85 	while (left_len != 0) {
86 		/*
87 		 * Extract the next path component and adjust `left'
88 		 * and its length.
89 		 */
90 		p = strchr(left, '/');
91 
92 		next_token_len = p != NULL ? p - left : left_len;
93 		memcpy(next_token, left, next_token_len);
94 		next_token[next_token_len] = '\0';
95 
96 		if (p != NULL) {
97 			left_len -= next_token_len + 1;
98 			memmove(left, p + 1, left_len + 1);
99 		} else {
100 			left[0] = '\0';
101 			left_len = 0;
102 		}
103 
104 		if (resolved[resolved_len - 1] != '/') {
105 			if (resolved_len + 1 >= PATH_MAX) {
106 				errno = ENAMETOOLONG;
107 				return (NULL);
108 			}
109 			resolved[resolved_len++] = '/';
110 			resolved[resolved_len] = '\0';
111 		}
112 		if (next_token[0] == '\0') {
113 			/* Handle consequential slashes. */
114 			continue;
115 		} else if (strcmp(next_token, ".") == 0) {
116 			continue;
117 		} else if (strcmp(next_token, "..") == 0) {
118 			/*
119 			 * Strip the last path component except when we have
120 			 * single "/"
121 			 */
122 			if (resolved_len > 1) {
123 				resolved[resolved_len - 1] = '\0';
124 				q = strrchr(resolved, '/') + 1;
125 				*q = '\0';
126 				resolved_len = q - resolved;
127 			}
128 			continue;
129 		}
130 
131 		/*
132 		 * Append the next path component and lstat() it.
133 		 */
134 		resolved_len = strlcat(resolved, next_token, PATH_MAX);
135 		if (resolved_len >= PATH_MAX) {
136 			errno = ENAMETOOLONG;
137 			return (NULL);
138 		}
139 		if (lstat(resolved, &sb) != 0)
140 			return (NULL);
141 		if (S_ISLNK(sb.st_mode)) {
142 			if (symlinks++ > MAXSYMLINKS) {
143 				errno = ELOOP;
144 				return (NULL);
145 			}
146 			slen = readlink(resolved, symlink, sizeof(symlink));
147 			if (slen <= 0 || slen >= sizeof(symlink)) {
148 				if (slen < 0)
149 					; /* keep errno from readlink(2) call */
150 				else if (slen == 0)
151 					errno = ENOENT;
152 				else
153 					errno = ENAMETOOLONG;
154 				return (NULL);
155 			}
156 			symlink[slen] = '\0';
157 			if (symlink[0] == '/') {
158 				resolved[1] = 0;
159 				resolved_len = 1;
160 			} else {
161 				/* Strip the last path component. */
162 				q = strrchr(resolved, '/') + 1;
163 				*q = '\0';
164 				resolved_len = q - resolved;
165 			}
166 
167 			/*
168 			 * If there are any path components left, then
169 			 * append them to symlink. The result is placed
170 			 * in `left'.
171 			 */
172 			if (p != NULL) {
173 				if (symlink[slen - 1] != '/') {
174 					if (slen + 1 >= sizeof(symlink)) {
175 						errno = ENAMETOOLONG;
176 						return (NULL);
177 					}
178 					symlink[slen] = '/';
179 					symlink[slen + 1] = 0;
180 				}
181 				left_len = strlcat(symlink, left,
182 				    sizeof(symlink));
183 				if (left_len >= sizeof(symlink)) {
184 					errno = ENAMETOOLONG;
185 					return (NULL);
186 				}
187 			}
188 			left_len = strlcpy(left, symlink, sizeof(left));
189 		} else if (!S_ISDIR(sb.st_mode) && p != NULL) {
190 			errno = ENOTDIR;
191 			return (NULL);
192 		}
193 	}
194 
195 	/*
196 	 * Remove trailing slash except when the resolved pathname
197 	 * is a single "/".
198 	 */
199 	if (resolved_len > 1 && resolved[resolved_len - 1] == '/')
200 		resolved[resolved_len - 1] = '\0';
201 	return (resolved);
202 }
203 
204 char *
realpath(const char * __restrict path,char * __restrict resolved)205 realpath(const char * __restrict path, char * __restrict resolved)
206 {
207 	char *m, *res;
208 
209 	if (path == NULL) {
210 		errno = EINVAL;
211 		return (NULL);
212 	}
213 	if (path[0] == '\0') {
214 		errno = ENOENT;
215 		return (NULL);
216 	}
217 	if (resolved != NULL) {
218 		m = NULL;
219 	} else {
220 		m = resolved = malloc(PATH_MAX);
221 		if (resolved == NULL)
222 			return (NULL);
223 	}
224 	res = realpath1(path, resolved);
225 	if (res == NULL)
226 		free(m);
227 	return (res);
228 }
229