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1 /*
2 * dcookies.c
3 *
4 * Copyright 2002 John Levon <levon@movementarian.org>
5 *
6 * Persistent cookie-path mappings. These are used by
7 * profilers to convert a per-task EIP value into something
8 * non-transitory that can be processed at a later date.
9 * This is done by locking the dentry/vfsmnt pair in the
10 * kernel until released by the tasks needing the persistent
11 * objects. The tag is simply an unsigned long that refers
12 * to the pair and can be looked up from userspace.
13 */
14
15 #include <linux/syscalls.h>
16 #include <linux/export.h>
17 #include <linux/slab.h>
18 #include <linux/list.h>
19 #include <linux/mount.h>
20 #include <linux/capability.h>
21 #include <linux/dcache.h>
22 #include <linux/mm.h>
23 #include <linux/err.h>
24 #include <linux/errno.h>
25 #include <linux/dcookies.h>
26 #include <linux/mutex.h>
27 #include <linux/path.h>
28 #include <linux/compat.h>
29 #include <linux/uaccess.h>
30
31 /* The dcookies are allocated from a kmem_cache and
32 * hashed onto a small number of lists. None of the
33 * code here is particularly performance critical
34 */
35 struct dcookie_struct {
36 struct path path;
37 struct list_head hash_list;
38 };
39
40 static LIST_HEAD(dcookie_users);
41 static DEFINE_MUTEX(dcookie_mutex);
42 static struct kmem_cache *dcookie_cache __read_mostly;
43 static struct list_head *dcookie_hashtable __read_mostly;
44 static size_t hash_size __read_mostly;
45
46 static inline int is_live(void)
47 {
48 return !(list_empty(&dcookie_users));
49 }
50
51
52 /* The dentry is locked, its address will do for the cookie */
53 static inline unsigned long dcookie_value(struct dcookie_struct * dcs)
54 {
55 return (unsigned long)dcs->path.dentry;
56 }
57
58
59 static size_t dcookie_hash(unsigned long dcookie)
60 {
61 return (dcookie >> L1_CACHE_SHIFT) & (hash_size - 1);
62 }
63
64
65 static struct dcookie_struct * find_dcookie(unsigned long dcookie)
66 {
67 struct dcookie_struct *found = NULL;
68 struct dcookie_struct * dcs;
69 struct list_head * pos;
70 struct list_head * list;
71
72 list = dcookie_hashtable + dcookie_hash(dcookie);
73
74 list_for_each(pos, list) {
75 dcs = list_entry(pos, struct dcookie_struct, hash_list);
76 if (dcookie_value(dcs) == dcookie) {
77 found = dcs;
78 break;
79 }
80 }
81
82 return found;
83 }
84
85
86 static void hash_dcookie(struct dcookie_struct * dcs)
87 {
88 struct list_head * list = dcookie_hashtable + dcookie_hash(dcookie_value(dcs));
89 list_add(&dcs->hash_list, list);
90 }
91
92
93 static struct dcookie_struct *alloc_dcookie(const struct path *path)
94 {
95 struct dcookie_struct *dcs = kmem_cache_alloc(dcookie_cache,
96 GFP_KERNEL);
97 struct dentry *d;
98 if (!dcs)
99 return NULL;
100
101 d = path->dentry;
102 spin_lock(&d->d_lock);
103 d->d_flags |= DCACHE_COOKIE;
104 spin_unlock(&d->d_lock);
105
106 dcs->path = *path;
107 path_get(path);
108 hash_dcookie(dcs);
109 return dcs;
110 }
111
112
113 /* This is the main kernel-side routine that retrieves the cookie
114 * value for a dentry/vfsmnt pair.
115 */
116 int get_dcookie(const struct path *path, unsigned long *cookie)
117 {
118 int err = 0;
119 struct dcookie_struct * dcs;
120
121 mutex_lock(&dcookie_mutex);
122
123 if (!is_live()) {
124 err = -EINVAL;
125 goto out;
126 }
127
128 if (path->dentry->d_flags & DCACHE_COOKIE) {
129 dcs = find_dcookie((unsigned long)path->dentry);
130 } else {
131 dcs = alloc_dcookie(path);
132 if (!dcs) {
133 err = -ENOMEM;
134 goto out;
135 }
136 }
137
138 *cookie = dcookie_value(dcs);
139
140 out:
141 mutex_unlock(&dcookie_mutex);
142 return err;
143 }
144
145
146 /* And here is where the userspace process can look up the cookie value
147 * to retrieve the path.
148 */
149 SYSCALL_DEFINE3(lookup_dcookie, u64, cookie64, char __user *, buf, size_t, len)
150 {
151 unsigned long cookie = (unsigned long)cookie64;
152 int err = -EINVAL;
153 char * kbuf;
154 char * path;
155 size_t pathlen;
156 struct dcookie_struct * dcs;
157
158 /* we could leak path information to users
159 * without dir read permission without this
160 */
161 if (!capable(CAP_SYS_ADMIN))
162 return -EPERM;
163
164 mutex_lock(&dcookie_mutex);
165
166 if (!is_live()) {
167 err = -EINVAL;
168 goto out;
169 }
170
171 if (!(dcs = find_dcookie(cookie)))
172 goto out;
173
174 err = -ENOMEM;
175 kbuf = kmalloc(PAGE_SIZE, GFP_KERNEL);
176 if (!kbuf)
177 goto out;
178
179 /* FIXME: (deleted) ? */
180 path = d_path(&dcs->path, kbuf, PAGE_SIZE);
181
182 mutex_unlock(&dcookie_mutex);
183
184 if (IS_ERR(path)) {
185 err = PTR_ERR(path);
186 goto out_free;
187 }
188
189 err = -ERANGE;
190
191 pathlen = kbuf + PAGE_SIZE - path;
192 if (pathlen <= len) {
193 err = pathlen;
194 if (copy_to_user(buf, path, pathlen))
195 err = -EFAULT;
196 }
197
198 out_free:
199 kfree(kbuf);
200 return err;
201 out:
202 mutex_unlock(&dcookie_mutex);
203 return err;
204 }
205
206 #ifdef CONFIG_COMPAT
207 COMPAT_SYSCALL_DEFINE4(lookup_dcookie, u32, w0, u32, w1, char __user *, buf, compat_size_t, len)
208 {
209 #ifdef __BIG_ENDIAN
210 return sys_lookup_dcookie(((u64)w0 << 32) | w1, buf, len);
211 #else
212 return sys_lookup_dcookie(((u64)w1 << 32) | w0, buf, len);
213 #endif
214 }
215 #endif
216
217 static int dcookie_init(void)
218 {
219 struct list_head * d;
220 unsigned int i, hash_bits;
221 int err = -ENOMEM;
222
223 dcookie_cache = kmem_cache_create("dcookie_cache",
224 sizeof(struct dcookie_struct),
225 0, 0, NULL);
226
227 if (!dcookie_cache)
228 goto out;
229
230 dcookie_hashtable = kmalloc(PAGE_SIZE, GFP_KERNEL);
231 if (!dcookie_hashtable)
232 goto out_kmem;
233
234 err = 0;
235
236 /*
237 * Find the power-of-two list-heads that can fit into the allocation..
238 * We don't guarantee that "sizeof(struct list_head)" is necessarily
239 * a power-of-two.
240 */
241 hash_size = PAGE_SIZE / sizeof(struct list_head);
242 hash_bits = 0;
243 do {
244 hash_bits++;
245 } while ((hash_size >> hash_bits) != 0);
246 hash_bits--;
247
248 /*
249 * Re-calculate the actual number of entries and the mask
250 * from the number of bits we can fit.
251 */
252 hash_size = 1UL << hash_bits;
253
254 /* And initialize the newly allocated array */
255 d = dcookie_hashtable;
256 i = hash_size;
257 do {
258 INIT_LIST_HEAD(d);
259 d++;
260 i--;
261 } while (i);
262
263 out:
264 return err;
265 out_kmem:
266 kmem_cache_destroy(dcookie_cache);
267 goto out;
268 }
269
270
271 static void free_dcookie(struct dcookie_struct * dcs)
272 {
273 struct dentry *d = dcs->path.dentry;
274
275 spin_lock(&d->d_lock);
276 d->d_flags &= ~DCACHE_COOKIE;
277 spin_unlock(&d->d_lock);
278
279 path_put(&dcs->path);
280 kmem_cache_free(dcookie_cache, dcs);
281 }
282
283
284 static void dcookie_exit(void)
285 {
286 struct list_head * list;
287 struct list_head * pos;
288 struct list_head * pos2;
289 struct dcookie_struct * dcs;
290 size_t i;
291
292 for (i = 0; i < hash_size; ++i) {
293 list = dcookie_hashtable + i;
294 list_for_each_safe(pos, pos2, list) {
295 dcs = list_entry(pos, struct dcookie_struct, hash_list);
296 list_del(&dcs->hash_list);
297 free_dcookie(dcs);
298 }
299 }
300
301 kfree(dcookie_hashtable);
302 kmem_cache_destroy(dcookie_cache);
303 }
304
305
306 struct dcookie_user {
307 struct list_head next;
308 };
309
310 struct dcookie_user * dcookie_register(void)
311 {
312 struct dcookie_user * user;
313
314 mutex_lock(&dcookie_mutex);
315
316 user = kmalloc(sizeof(struct dcookie_user), GFP_KERNEL);
317 if (!user)
318 goto out;
319
320 if (!is_live() && dcookie_init())
321 goto out_free;
322
323 list_add(&user->next, &dcookie_users);
324
325 out:
326 mutex_unlock(&dcookie_mutex);
327 return user;
328 out_free:
329 kfree(user);
330 user = NULL;
331 goto out;
332 }
333
334
335 void dcookie_unregister(struct dcookie_user * user)
336 {
337 mutex_lock(&dcookie_mutex);
338
339 list_del(&user->next);
340 kfree(user);
341
342 if (!is_live())
343 dcookie_exit();
344
345 mutex_unlock(&dcookie_mutex);
346 }
347
348 EXPORT_SYMBOL_GPL(dcookie_register);
349 EXPORT_SYMBOL_GPL(dcookie_unregister);
350 EXPORT_SYMBOL_GPL(get_dcookie);