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1 | /* Return the canonical absolute name of a given file inside chroot. | |
2 | Copyright (C) 1996-2019 Free Software Foundation, Inc. | |
3 | This file is part of the GNU C Library. | |
4 | ||
5 | This program is free software; you can redistribute it and/or modify | |
6 | it under the terms of the GNU General Public License as published | |
7 | by the Free Software Foundation; version 2 of the License, or | |
8 | (at your option) any later version. | |
9 | ||
10 | This program is distributed in the hope that it will be useful, | |
11 | but WITHOUT ANY WARRANTY; without even the implied warranty of | |
12 | MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the | |
13 | GNU General Public License for more details. | |
14 | ||
15 | You should have received a copy of the GNU General Public License | |
16 | along with this program; if not, see <http://www.gnu.org/licenses/>. */ | |
17 | ||
18 | #include <stdlib.h> | |
19 | #include <string.h> | |
20 | #include <unistd.h> | |
21 | #include <limits.h> | |
22 | #include <sys/stat.h> | |
23 | #include <errno.h> | |
24 | #include <stddef.h> | |
25 | #include <stdint.h> | |
26 | ||
27 | #include <eloop-threshold.h> | |
28 | #include <ldconfig.h> | |
29 | ||
30 | #ifndef PATH_MAX | |
31 | #define PATH_MAX 1024 | |
32 | #endif | |
33 | ||
34 | /* Return the canonical absolute name of file NAME as if chroot(CHROOT) was | |
35 | done first. A canonical name does not contain any `.', `..' components | |
36 | nor any repeated path separators ('/') or symlinks. All path components | |
37 | must exist and NAME must be absolute filename. The result is malloc'd. | |
38 | The returned name includes the CHROOT prefix. */ | |
39 | ||
40 | char * | |
41 | chroot_canon (const char *chroot, const char *name) | |
42 | { | |
43 | char *rpath; | |
44 | char *dest; | |
45 | char *extra_buf = NULL; | |
46 | char *rpath_root; | |
47 | const char *start; | |
48 | const char *end; | |
49 | const char *rpath_limit; | |
50 | int num_links = 0; | |
51 | size_t chroot_len = strlen (chroot); | |
52 | ||
53 | if (chroot_len < 1) | |
54 | { | |
55 | __set_errno (EINVAL); | |
56 | return NULL; | |
57 | } | |
58 | ||
59 | rpath = xmalloc (chroot_len + PATH_MAX); | |
60 | ||
61 | rpath_limit = rpath + chroot_len + PATH_MAX; | |
62 | ||
63 | rpath_root = (char *) mempcpy (rpath, chroot, chroot_len) - 1; | |
64 | if (*rpath_root != '/') | |
65 | *++rpath_root = '/'; | |
66 | dest = rpath_root + 1; | |
67 | ||
68 | for (start = end = name; *start; start = end) | |
69 | { | |
70 | struct stat64 st; | |
71 | ||
72 | /* Skip sequence of multiple path-separators. */ | |
73 | while (*start == '/') | |
74 | ++start; | |
75 | ||
76 | /* Find end of path component. */ | |
77 | for (end = start; *end && *end != '/'; ++end) | |
78 | /* Nothing. */; | |
79 | ||
80 | if (end - start == 0) | |
81 | break; | |
82 | else if (end - start == 1 && start[0] == '.') | |
83 | /* nothing */; | |
84 | else if (end - start == 2 && start[0] == '.' && start[1] == '.') | |
85 | { | |
86 | /* Back up to previous component, ignore if at root already. */ | |
87 | if (dest > rpath_root + 1) | |
88 | while ((--dest)[-1] != '/'); | |
89 | } | |
90 | else | |
91 | { | |
92 | size_t new_size; | |
93 | ||
94 | if (dest[-1] != '/') | |
95 | *dest++ = '/'; | |
96 | ||
97 | if (dest + (end - start) >= rpath_limit) | |
98 | { | |
99 | ptrdiff_t dest_offset = dest - rpath; | |
100 | char *new_rpath; | |
101 | ||
102 | new_size = rpath_limit - rpath; | |
103 | if (end - start + 1 > PATH_MAX) | |
104 | new_size += end - start + 1; | |
105 | else | |
106 | new_size += PATH_MAX; | |
107 | new_rpath = (char *) xrealloc (rpath, new_size); | |
108 | rpath = new_rpath; | |
109 | rpath_limit = rpath + new_size; | |
110 | ||
111 | dest = rpath + dest_offset; | |
112 | } | |
113 | ||
114 | dest = mempcpy (dest, start, end - start); | |
115 | *dest = '\0'; | |
116 | ||
117 | if (lstat64 (rpath, &st) < 0) | |
118 | { | |
119 | if (*end == '\0') | |
120 | goto done; | |
121 | goto error; | |
122 | } | |
123 | ||
124 | if (S_ISLNK (st.st_mode)) | |
125 | { | |
126 | char *buf = alloca (PATH_MAX); | |
127 | size_t len; | |
128 | ||
129 | if (++num_links > __eloop_threshold ()) | |
130 | { | |
131 | __set_errno (ELOOP); | |
132 | goto error; | |
133 | } | |
134 | ||
135 | ssize_t n = readlink (rpath, buf, PATH_MAX - 1); | |
136 | if (n < 0) | |
137 | { | |
138 | if (*end == '\0') | |
139 | goto done; | |
140 | goto error; | |
141 | } | |
142 | buf[n] = '\0'; | |
143 | ||
144 | if (!extra_buf) | |
145 | extra_buf = alloca (PATH_MAX); | |
146 | ||
147 | len = strlen (end); | |
148 | if (len >= PATH_MAX - n) | |
149 | { | |
150 | __set_errno (ENAMETOOLONG); | |
151 | goto error; | |
152 | } | |
153 | ||
154 | /* Careful here, end may be a pointer into extra_buf... */ | |
155 | memmove (&extra_buf[n], end, len + 1); | |
156 | name = end = memcpy (extra_buf, buf, n); | |
157 | ||
158 | if (buf[0] == '/') | |
159 | dest = rpath_root + 1; /* It's an absolute symlink */ | |
160 | else | |
161 | /* Back up to previous component, ignore if at root already: */ | |
162 | if (dest > rpath_root + 1) | |
163 | while ((--dest)[-1] != '/'); | |
164 | } | |
165 | } | |
166 | } | |
167 | done: | |
168 | if (dest > rpath_root + 1 && dest[-1] == '/') | |
169 | --dest; | |
170 | *dest = '\0'; | |
171 | ||
172 | return rpath; | |
173 | ||
174 | error: | |
175 | free (rpath); | |
176 | return NULL; | |
177 | } |