1 /* $OpenBSD: sftp-realpath.c,v 1.2 2021/09/02 21:03:54 deraadt Exp $ */
2 /*
3 * Copyright (c) 2003 Constantin S. Svintsoff <kostik@iclub.nsu.ru>
4 *
5 * Redistribution and use in source and binary forms, with or without
6 * modification, are permitted provided that the following conditions
7 * are met:
8 * 1. Redistributions of source code must retain the above copyright
9 * notice, this list of conditions and the following disclaimer.
10 * 2. Redistributions in binary form must reproduce the above copyright
11 * notice, this list of conditions and the following disclaimer in the
12 * documentation and/or other materials provided with the distribution.
13 * 3. The names of the authors may not be used to endorse or promote
14 * products derived from this software without specific prior written
15 * permission.
16 *
17 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
18 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
19 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
20 * ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
21 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
22 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
23 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
24 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
25 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
26 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
27 * SUCH DAMAGE.
28 */
29
30 #include "includes.h"
31
32 #include <sys/types.h>
33 #include <sys/stat.h>
34
35 #include <errno.h>
36 #include <stdlib.h>
37 #include <stddef.h>
38 #include <string.h>
39 #include <unistd.h>
40 #include <limits.h>
41
42 #ifndef SYMLOOP_MAX
43 # define SYMLOOP_MAX 32
44 #endif
45
46 /* XXX rewrite sftp-server to use POSIX realpath and remove this hack */
47
48 char *sftp_realpath(const char *path, char *resolved);
49
50 /*
51 * char *realpath(const char *path, char resolved[PATH_MAX]);
52 *
53 * Find the real name of path, by removing all ".", ".." and symlink
54 * components. Returns (resolved) on success, or (NULL) on failure,
55 * in which case the path which caused trouble is left in (resolved).
56 */
57 char *
sftp_realpath(const char * path,char * resolved)58 sftp_realpath(const char *path, char *resolved)
59 {
60 struct stat sb;
61 char *p, *q, *s;
62 size_t left_len, resolved_len;
63 unsigned symlinks;
64 int serrno, slen, mem_allocated;
65 char left[PATH_MAX], next_token[PATH_MAX], symlink[PATH_MAX];
66
67 if (path[0] == '\0') {
68 errno = ENOENT;
69 return (NULL);
70 }
71
72 serrno = errno;
73
74 if (resolved == NULL) {
75 resolved = malloc(PATH_MAX);
76 if (resolved == NULL)
77 return (NULL);
78 mem_allocated = 1;
79 } else
80 mem_allocated = 0;
81
82 symlinks = 0;
83 if (path[0] == '/') {
84 resolved[0] = '/';
85 resolved[1] = '\0';
86 if (path[1] == '\0')
87 return (resolved);
88 resolved_len = 1;
89 left_len = strlcpy(left, path + 1, sizeof(left));
90 } else {
91 if (getcwd(resolved, PATH_MAX) == NULL) {
92 if (mem_allocated)
93 free(resolved);
94 else
95 strlcpy(resolved, ".", PATH_MAX);
96 return (NULL);
97 }
98 resolved_len = strlen(resolved);
99 left_len = strlcpy(left, path, sizeof(left));
100 }
101 if (left_len >= sizeof(left) || resolved_len >= PATH_MAX) {
102 errno = ENAMETOOLONG;
103 goto err;
104 }
105
106 /*
107 * Iterate over path components in `left'.
108 */
109 while (left_len != 0) {
110 /*
111 * Extract the next path component and adjust `left'
112 * and its length.
113 */
114 p = strchr(left, '/');
115 s = p ? p : left + left_len;
116 if (s - left >= (ptrdiff_t)sizeof(next_token)) {
117 errno = ENAMETOOLONG;
118 goto err;
119 }
120 memcpy(next_token, left, s - left);
121 next_token[s - left] = '\0';
122 left_len -= s - left;
123 if (p != NULL)
124 memmove(left, s + 1, left_len + 1);
125 if (resolved[resolved_len - 1] != '/') {
126 if (resolved_len + 1 >= PATH_MAX) {
127 errno = ENAMETOOLONG;
128 goto err;
129 }
130 resolved[resolved_len++] = '/';
131 resolved[resolved_len] = '\0';
132 }
133 if (next_token[0] == '\0')
134 continue;
135 else if (strcmp(next_token, ".") == 0)
136 continue;
137 else if (strcmp(next_token, "..") == 0) {
138 /*
139 * Strip the last path component except when we have
140 * single "/"
141 */
142 if (resolved_len > 1) {
143 resolved[resolved_len - 1] = '\0';
144 q = strrchr(resolved, '/') + 1;
145 *q = '\0';
146 resolved_len = q - resolved;
147 }
148 continue;
149 }
150
151 /*
152 * Append the next path component and lstat() it. If
153 * lstat() fails we still can return successfully if
154 * there are no more path components left.
155 */
156 resolved_len = strlcat(resolved, next_token, PATH_MAX);
157 if (resolved_len >= PATH_MAX) {
158 errno = ENAMETOOLONG;
159 goto err;
160 }
161 if (lstat(resolved, &sb) != 0) {
162 if (errno == ENOENT && p == NULL) {
163 errno = serrno;
164 return (resolved);
165 }
166 goto err;
167 }
168 if (S_ISLNK(sb.st_mode)) {
169 if (symlinks++ > SYMLOOP_MAX) {
170 errno = ELOOP;
171 goto err;
172 }
173 slen = readlink(resolved, symlink, sizeof(symlink) - 1);
174 if (slen < 0)
175 goto err;
176 symlink[slen] = '\0';
177 if (symlink[0] == '/') {
178 resolved[1] = 0;
179 resolved_len = 1;
180 } else if (resolved_len > 1) {
181 /* Strip the last path component. */
182 resolved[resolved_len - 1] = '\0';
183 q = strrchr(resolved, '/') + 1;
184 *q = '\0';
185 resolved_len = q - resolved;
186 }
187
188 /*
189 * If there are any path components left, then
190 * append them to symlink. The result is placed
191 * in `left'.
192 */
193 if (p != NULL) {
194 if (symlink[slen - 1] != '/') {
195 if (slen + 1 >=
196 (ptrdiff_t)sizeof(symlink)) {
197 errno = ENAMETOOLONG;
198 goto err;
199 }
200 symlink[slen] = '/';
201 symlink[slen + 1] = 0;
202 }
203 left_len = strlcat(symlink, left, sizeof(symlink));
204 if (left_len >= sizeof(symlink)) {
205 errno = ENAMETOOLONG;
206 goto err;
207 }
208 }
209 left_len = strlcpy(left, symlink, sizeof(left));
210 }
211 }
212
213 /*
214 * Remove trailing slash except when the resolved pathname
215 * is a single "/".
216 */
217 if (resolved_len > 1 && resolved[resolved_len - 1] == '/')
218 resolved[resolved_len - 1] = '\0';
219 return (resolved);
220
221 err:
222 if (mem_allocated)
223 free(resolved);
224 return (NULL);
225 }
226