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 */
35struct dcookie_struct {
36 struct path path;
37 struct list_head hash_list;
38};
39
40static LIST_HEAD(dcookie_users);
41static DEFINE_MUTEX(dcookie_mutex);
42static struct kmem_cache *dcookie_cache __read_mostly;
43static struct list_head *dcookie_hashtable __read_mostly;
44static size_t hash_size __read_mostly;
45
46static 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 */
53static inline unsigned long dcookie_value(struct dcookie_struct * dcs)
54{
55 return (unsigned long)dcs->path.dentry;
56}
57
58
59static size_t dcookie_hash(unsigned long dcookie)
60{
61 return (dcookie >> L1_CACHE_SHIFT) & (hash_size - 1);
62}
63
64
65static 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
86static 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
93static 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 */
116int 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
140out:
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 */
149static int do_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
198out_free:
199 kfree(kbuf);
200 return err;
201out:
202 mutex_unlock(&dcookie_mutex);
203 return err;
204}
205
206SYSCALL_DEFINE3(lookup_dcookie, u64, cookie64, char __user *, buf, size_t, len)
207{
208 return do_lookup_dcookie(cookie64, buf, len);
209}
210
211#ifdef CONFIG_COMPAT
212COMPAT_SYSCALL_DEFINE4(lookup_dcookie, u32, w0, u32, w1, char __user *, buf, compat_size_t, len)
213{
214#ifdef __BIG_ENDIAN
215 return do_lookup_dcookie(((u64)w0 << 32) | w1, buf, len);
216#else
217 return do_lookup_dcookie(((u64)w1 << 32) | w0, buf, len);
218#endif
219}
220#endif
221
222static int dcookie_init(void)
223{
224 struct list_head * d;
225 unsigned int i, hash_bits;
226 int err = -ENOMEM;
227
228 dcookie_cache = kmem_cache_create("dcookie_cache",
229 sizeof(struct dcookie_struct),
230 0, 0, NULL);
231
232 if (!dcookie_cache)
233 goto out;
234
235 dcookie_hashtable = kmalloc(PAGE_SIZE, GFP_KERNEL);
236 if (!dcookie_hashtable)
237 goto out_kmem;
238
239 err = 0;
240
241 /*
242 * Find the power-of-two list-heads that can fit into the allocation..
243 * We don't guarantee that "sizeof(struct list_head)" is necessarily
244 * a power-of-two.
245 */
246 hash_size = PAGE_SIZE / sizeof(struct list_head);
247 hash_bits = 0;
248 do {
249 hash_bits++;
250 } while ((hash_size >> hash_bits) != 0);
251 hash_bits--;
252
253 /*
254 * Re-calculate the actual number of entries and the mask
255 * from the number of bits we can fit.
256 */
257 hash_size = 1UL << hash_bits;
258
259 /* And initialize the newly allocated array */
260 d = dcookie_hashtable;
261 i = hash_size;
262 do {
263 INIT_LIST_HEAD(d);
264 d++;
265 i--;
266 } while (i);
267
268out:
269 return err;
270out_kmem:
271 kmem_cache_destroy(dcookie_cache);
272 goto out;
273}
274
275
276static void free_dcookie(struct dcookie_struct * dcs)
277{
278 struct dentry *d = dcs->path.dentry;
279
280 spin_lock(&d->d_lock);
281 d->d_flags &= ~DCACHE_COOKIE;
282 spin_unlock(&d->d_lock);
283
284 path_put(&dcs->path);
285 kmem_cache_free(dcookie_cache, dcs);
286}
287
288
289static void dcookie_exit(void)
290{
291 struct list_head * list;
292 struct list_head * pos;
293 struct list_head * pos2;
294 struct dcookie_struct * dcs;
295 size_t i;
296
297 for (i = 0; i < hash_size; ++i) {
298 list = dcookie_hashtable + i;
299 list_for_each_safe(pos, pos2, list) {
300 dcs = list_entry(pos, struct dcookie_struct, hash_list);
301 list_del(&dcs->hash_list);
302 free_dcookie(dcs);
303 }
304 }
305
306 kfree(dcookie_hashtable);
307 kmem_cache_destroy(dcookie_cache);
308}
309
310
311struct dcookie_user {
312 struct list_head next;
313};
314
315struct dcookie_user * dcookie_register(void)
316{
317 struct dcookie_user * user;
318
319 mutex_lock(&dcookie_mutex);
320
321 user = kmalloc(sizeof(struct dcookie_user), GFP_KERNEL);
322 if (!user)
323 goto out;
324
325 if (!is_live() && dcookie_init())
326 goto out_free;
327
328 list_add(&user->next, &dcookie_users);
329
330out:
331 mutex_unlock(&dcookie_mutex);
332 return user;
333out_free:
334 kfree(user);
335 user = NULL;
336 goto out;
337}
338
339
340void dcookie_unregister(struct dcookie_user * user)
341{
342 mutex_lock(&dcookie_mutex);
343
344 list_del(&user->next);
345 kfree(user);
346
347 if (!is_live())
348 dcookie_exit();
349
350 mutex_unlock(&dcookie_mutex);
351}
352
353EXPORT_SYMBOL_GPL(dcookie_register);
354EXPORT_SYMBOL_GPL(dcookie_unregister);
355EXPORT_SYMBOL_GPL(get_dcookie);
356