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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 <asm/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(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(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, 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); |
351 |
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