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