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328970de | 1 | // SPDX-License-Identifier: GPL-2.0-or-later |
7063fbf2 JB |
2 | /* -*- mode: c; c-basic-offset: 8; -*- |
3 | * vim: noexpandtab sw=8 ts=8 sts=0: | |
4 | * | |
5 | * symlink.c - operations for configfs symlinks. | |
6 | * | |
7063fbf2 JB |
7 | * Based on sysfs: |
8 | * sysfs is Copyright (C) 2001, 2002, 2003 Patrick Mochel | |
9 | * | |
10 | * configfs Copyright (C) 2005 Oracle. All rights reserved. | |
11 | */ | |
12 | ||
13 | #include <linux/fs.h> | |
14 | #include <linux/module.h> | |
15 | #include <linux/namei.h> | |
5a0e3ad6 | 16 | #include <linux/slab.h> |
7063fbf2 JB |
17 | |
18 | #include <linux/configfs.h> | |
19 | #include "configfs_internal.h" | |
20 | ||
9a73d78c LR |
21 | /* Protects attachments of new symlinks */ |
22 | DEFINE_MUTEX(configfs_symlink_mutex); | |
23 | ||
7063fbf2 JB |
24 | static int item_depth(struct config_item * item) |
25 | { | |
26 | struct config_item * p = item; | |
27 | int depth = 0; | |
28 | do { depth++; } while ((p = p->ci_parent) && !configfs_is_root(p)); | |
29 | return depth; | |
30 | } | |
31 | ||
32 | static int item_path_length(struct config_item * item) | |
33 | { | |
34 | struct config_item * p = item; | |
35 | int length = 1; | |
36 | do { | |
37 | length += strlen(config_item_name(p)) + 1; | |
38 | p = p->ci_parent; | |
39 | } while (p && !configfs_is_root(p)); | |
40 | return length; | |
41 | } | |
42 | ||
43 | static void fill_item_path(struct config_item * item, char * buffer, int length) | |
44 | { | |
45 | struct config_item * p; | |
46 | ||
47 | --length; | |
48 | for (p = item; p && !configfs_is_root(p); p = p->ci_parent) { | |
49 | int cur = strlen(config_item_name(p)); | |
50 | ||
51 | /* back up enough to print this bus id with '/' */ | |
52 | length -= cur; | |
1823342a | 53 | memcpy(buffer + length, config_item_name(p), cur); |
7063fbf2 JB |
54 | *(buffer + --length) = '/'; |
55 | } | |
56 | } | |
57 | ||
e9c03af2 AV |
58 | static int configfs_get_target_path(struct config_item *item, |
59 | struct config_item *target, char *path) | |
60 | { | |
61 | int depth, size; | |
62 | char *s; | |
63 | ||
64 | depth = item_depth(item); | |
65 | size = item_path_length(target) + depth * 3 - 1; | |
66 | if (size > PATH_MAX) | |
67 | return -ENAMETOOLONG; | |
68 | ||
69 | pr_debug("%s: depth = %d, size = %d\n", __func__, depth, size); | |
70 | ||
71 | for (s = path; depth--; s += 3) | |
72 | strcpy(s,"../"); | |
73 | ||
74 | fill_item_path(target, path, size); | |
75 | pr_debug("%s: path = '%s'\n", __func__, path); | |
76 | return 0; | |
77 | } | |
78 | ||
7063fbf2 | 79 | static int create_link(struct config_item *parent_item, |
e7515d06 | 80 | struct config_item *item, |
7063fbf2 JB |
81 | struct dentry *dentry) |
82 | { | |
83 | struct configfs_dirent *target_sd = item->ci_dentry->d_fsdata; | |
e9c03af2 | 84 | char *body; |
7063fbf2 JB |
85 | int ret; |
86 | ||
2a109f2a | 87 | if (!configfs_dirent_is_ready(target_sd)) |
e9c03af2 AV |
88 | return -ENOENT; |
89 | ||
90 | body = kzalloc(PAGE_SIZE, GFP_KERNEL); | |
91 | if (!body) | |
92 | return -ENOMEM; | |
93 | ||
94 | configfs_get(target_sd); | |
95 | spin_lock(&configfs_dirent_lock); | |
96 | if (target_sd->s_type & CONFIGFS_USET_DROPPING) { | |
97 | spin_unlock(&configfs_dirent_lock); | |
98 | configfs_put(target_sd); | |
99 | kfree(body); | |
100 | return -ENOENT; | |
101 | } | |
102 | target_sd->s_links++; | |
103 | spin_unlock(&configfs_dirent_lock); | |
e2f238f7 | 104 | ret = configfs_get_target_path(parent_item, item, body); |
e9c03af2 AV |
105 | if (!ret) |
106 | ret = configfs_create_link(target_sd, parent_item->ci_dentry, | |
107 | dentry, body); | |
108 | if (ret) { | |
5301a77d | 109 | spin_lock(&configfs_dirent_lock); |
e9c03af2 | 110 | target_sd->s_links--; |
5301a77d | 111 | spin_unlock(&configfs_dirent_lock); |
e9c03af2 AV |
112 | configfs_put(target_sd); |
113 | kfree(body); | |
7063fbf2 | 114 | } |
7063fbf2 JB |
115 | return ret; |
116 | } | |
117 | ||
118 | ||
421748ec | 119 | static int get_target(const char *symname, struct path *path, |
b7c177fc | 120 | struct config_item **target, struct super_block *sb) |
7063fbf2 JB |
121 | { |
122 | int ret; | |
123 | ||
421748ec | 124 | ret = kern_path(symname, LOOKUP_FOLLOW|LOOKUP_DIRECTORY, path); |
7063fbf2 | 125 | if (!ret) { |
b7c177fc | 126 | if (path->dentry->d_sb == sb) { |
421748ec | 127 | *target = configfs_get_config_item(path->dentry); |
7063fbf2 JB |
128 | if (!*target) { |
129 | ret = -ENOENT; | |
421748ec | 130 | path_put(path); |
7063fbf2 | 131 | } |
9b6e3102 | 132 | } else { |
7063fbf2 | 133 | ret = -EPERM; |
9b6e3102 AV |
134 | path_put(path); |
135 | } | |
7063fbf2 JB |
136 | } |
137 | ||
138 | return ret; | |
139 | } | |
140 | ||
141 | ||
142 | int configfs_symlink(struct inode *dir, struct dentry *dentry, const char *symname) | |
143 | { | |
144 | int ret; | |
421748ec | 145 | struct path path; |
2a109f2a | 146 | struct configfs_dirent *sd; |
7063fbf2 | 147 | struct config_item *parent_item; |
3c48f23a | 148 | struct config_item *target_item = NULL; |
aa293583 | 149 | const struct config_item_type *type; |
7063fbf2 | 150 | |
2a109f2a LR |
151 | sd = dentry->d_parent->d_fsdata; |
152 | /* | |
153 | * Fake invisibility if dir belongs to a group/default groups hierarchy | |
154 | * being attached | |
155 | */ | |
2a109f2a | 156 | if (!configfs_dirent_is_ready(sd)) |
e9c03af2 | 157 | return -ENOENT; |
2a109f2a | 158 | |
7063fbf2 JB |
159 | parent_item = configfs_get_config_item(dentry->d_parent); |
160 | type = parent_item->ci_type; | |
161 | ||
2a109f2a | 162 | ret = -EPERM; |
7063fbf2 JB |
163 | if (!type || !type->ct_item_ops || |
164 | !type->ct_item_ops->allow_link) | |
165 | goto out_put; | |
166 | ||
351e5d86 AV |
167 | /* |
168 | * This is really sick. What they wanted was a hybrid of | |
169 | * link(2) and symlink(2) - they wanted the target resolved | |
170 | * at syscall time (as link(2) would've done), be a directory | |
171 | * (which link(2) would've refused to do) *AND* be a deep | |
172 | * fucking magic, making the target busy from rmdir POV. | |
173 | * symlink(2) is nothing of that sort, and the locking it | |
174 | * gets matches the normal symlink(2) semantics. Without | |
175 | * attempts to resolve the target (which might very well | |
176 | * not even exist yet) done prior to locking the parent | |
177 | * directory. This perversion, OTOH, needs to resolve | |
178 | * the target, which would lead to obvious deadlocks if | |
179 | * attempted with any directories locked. | |
180 | * | |
181 | * Unfortunately, that garbage is userland ABI and we should've | |
182 | * said "no" back in 2005. Too late now, so we get to | |
183 | * play very ugly games with locking. | |
184 | * | |
185 | * Try *ANYTHING* of that sort in new code, and you will | |
186 | * really regret it. Just ask yourself - what could a BOFH | |
187 | * do to me and do I want to find it out first-hand? | |
188 | * | |
189 | * AV, a thoroughly annoyed bastard. | |
190 | */ | |
191 | inode_unlock(dir); | |
b7c177fc | 192 | ret = get_target(symname, &path, &target_item, dentry->d_sb); |
351e5d86 | 193 | inode_lock(dir); |
7063fbf2 JB |
194 | if (ret) |
195 | goto out_put; | |
196 | ||
351e5d86 AV |
197 | if (dentry->d_inode || d_unhashed(dentry)) |
198 | ret = -EEXIST; | |
199 | else | |
200 | ret = inode_permission(dir, MAY_WRITE | MAY_EXEC); | |
201 | if (!ret) | |
202 | ret = type->ct_item_ops->allow_link(parent_item, target_item); | |
e7520651 | 203 | if (!ret) { |
9a73d78c | 204 | mutex_lock(&configfs_symlink_mutex); |
7063fbf2 | 205 | ret = create_link(parent_item, target_item, dentry); |
9a73d78c | 206 | mutex_unlock(&configfs_symlink_mutex); |
e7520651 LR |
207 | if (ret && type->ct_item_ops->drop_link) |
208 | type->ct_item_ops->drop_link(parent_item, | |
209 | target_item); | |
210 | } | |
7063fbf2 JB |
211 | |
212 | config_item_put(target_item); | |
421748ec | 213 | path_put(&path); |
7063fbf2 JB |
214 | |
215 | out_put: | |
216 | config_item_put(parent_item); | |
7063fbf2 JB |
217 | return ret; |
218 | } | |
219 | ||
220 | int configfs_unlink(struct inode *dir, struct dentry *dentry) | |
221 | { | |
e9c03af2 | 222 | struct configfs_dirent *sd = dentry->d_fsdata, *target_sd; |
7063fbf2 | 223 | struct config_item *parent_item; |
aa293583 | 224 | const struct config_item_type *type; |
7063fbf2 JB |
225 | int ret; |
226 | ||
227 | ret = -EPERM; /* What lack-of-symlink returns */ | |
228 | if (!(sd->s_type & CONFIGFS_ITEM_LINK)) | |
229 | goto out; | |
230 | ||
e9c03af2 | 231 | target_sd = sd->s_element; |
7063fbf2 JB |
232 | |
233 | parent_item = configfs_get_config_item(dentry->d_parent); | |
234 | type = parent_item->ci_type; | |
235 | ||
6f610764 | 236 | spin_lock(&configfs_dirent_lock); |
7063fbf2 | 237 | list_del_init(&sd->s_sibling); |
6f610764 | 238 | spin_unlock(&configfs_dirent_lock); |
7063fbf2 JB |
239 | configfs_drop_dentry(sd, dentry->d_parent); |
240 | dput(dentry); | |
241 | configfs_put(sd); | |
242 | ||
243 | /* | |
244 | * drop_link() must be called before | |
e9c03af2 | 245 | * decrementing target's ->s_links, so that the order of |
7063fbf2 JB |
246 | * drop_link(this, target) and drop_item(target) is preserved. |
247 | */ | |
248 | if (type && type->ct_item_ops && | |
249 | type->ct_item_ops->drop_link) | |
250 | type->ct_item_ops->drop_link(parent_item, | |
e9c03af2 | 251 | target_sd->s_element); |
7063fbf2 | 252 | |
5301a77d | 253 | spin_lock(&configfs_dirent_lock); |
e9c03af2 | 254 | target_sd->s_links--; |
5301a77d | 255 | spin_unlock(&configfs_dirent_lock); |
e9c03af2 | 256 | configfs_put(target_sd); |
7063fbf2 JB |
257 | |
258 | config_item_put(parent_item); | |
259 | ||
260 | ret = 0; | |
261 | ||
262 | out: | |
263 | return ret; | |
264 | } | |
265 | ||
754661f1 | 266 | const struct inode_operations configfs_symlink_inode_operations = { |
e9c03af2 | 267 | .get_link = simple_get_link, |
3d0f89bb | 268 | .setattr = configfs_setattr, |
7063fbf2 JB |
269 | }; |
270 |