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