1 // SPDX-License-Identifier: GPL-2.0-only
2 /*
3 * dcookies.c
4 *
5 * Copyright 2002 John Levon <levon@movementarian.org>
6 *
7 * Persistent cookie-path mappings. These are used by
8 * profilers to convert a per-task EIP value into something
9 * non-transitory that can be processed at a later date.
10 * This is done by locking the dentry/vfsmnt pair in the
11 * kernel until released by the tasks needing the persistent
12 * objects. The tag is simply an unsigned long that refers
13 * to the pair and can be looked up from userspace.
14 */
15
16 #include <linux/syscalls.h>
17 #include <linux/export.h>
18 #include <linux/slab.h>
19 #include <linux/list.h>
20 #include <linux/mount.h>
21 #include <linux/capability.h>
22 #include <linux/dcache.h>
23 #include <linux/mm.h>
24 #include <linux/err.h>
25 #include <linux/errno.h>
26 #include <linux/dcookies.h>
27 #include <linux/mutex.h>
28 #include <linux/path.h>
29 #include <linux/compat.h>
30 #include <linux/uaccess.h>
31
32 /* The dcookies are allocated from a kmem_cache and
33 * hashed onto a small number of lists. None of the
34 * code here is particularly performance critical
35 */
36 struct dcookie_struct {
37 struct path path;
38 struct list_head hash_list;
39 };
40
41 static LIST_HEAD(dcookie_users);
42 static DEFINE_MUTEX(dcookie_mutex);
43 static struct kmem_cache *dcookie_cache __read_mostly;
44 static struct list_head *dcookie_hashtable __read_mostly;
45 static size_t hash_size __read_mostly;
46
is_live(void)47 static inline int is_live(void)
48 {
49 return !(list_empty(&dcookie_users));
50 }
51
52
53 /* The dentry is locked, its address will do for the cookie */
dcookie_value(struct dcookie_struct * dcs)54 static inline unsigned long dcookie_value(struct dcookie_struct * dcs)
55 {
56 return (unsigned long)dcs->path.dentry;
57 }
58
59
dcookie_hash(unsigned long dcookie)60 static size_t dcookie_hash(unsigned long dcookie)
61 {
62 return (dcookie >> L1_CACHE_SHIFT) & (hash_size - 1);
63 }
64
65
find_dcookie(unsigned long dcookie)66 static struct dcookie_struct * find_dcookie(unsigned long dcookie)
67 {
68 struct dcookie_struct *found = NULL;
69 struct dcookie_struct * dcs;
70 struct list_head * pos;
71 struct list_head * list;
72
73 list = dcookie_hashtable + dcookie_hash(dcookie);
74
75 list_for_each(pos, list) {
76 dcs = list_entry(pos, struct dcookie_struct, hash_list);
77 if (dcookie_value(dcs) == dcookie) {
78 found = dcs;
79 break;
80 }
81 }
82
83 return found;
84 }
85
86
hash_dcookie(struct dcookie_struct * dcs)87 static void hash_dcookie(struct dcookie_struct * dcs)
88 {
89 struct list_head * list = dcookie_hashtable + dcookie_hash(dcookie_value(dcs));
90 list_add(&dcs->hash_list, list);
91 }
92
93
alloc_dcookie(const struct path * path)94 static struct dcookie_struct *alloc_dcookie(const struct path *path)
95 {
96 struct dcookie_struct *dcs = kmem_cache_alloc(dcookie_cache,
97 GFP_KERNEL);
98 struct dentry *d;
99 if (!dcs)
100 return NULL;
101
102 d = path->dentry;
103 spin_lock(&d->d_lock);
104 d->d_flags |= DCACHE_COOKIE;
105 spin_unlock(&d->d_lock);
106
107 dcs->path = *path;
108 path_get(path);
109 hash_dcookie(dcs);
110 return dcs;
111 }
112
113
114 /* This is the main kernel-side routine that retrieves the cookie
115 * value for a dentry/vfsmnt pair.
116 */
get_dcookie(const struct path * path,unsigned long * cookie)117 int get_dcookie(const struct path *path, unsigned long *cookie)
118 {
119 int err = 0;
120 struct dcookie_struct * dcs;
121
122 mutex_lock(&dcookie_mutex);
123
124 if (!is_live()) {
125 err = -EINVAL;
126 goto out;
127 }
128
129 if (path->dentry->d_flags & DCACHE_COOKIE) {
130 dcs = find_dcookie((unsigned long)path->dentry);
131 } else {
132 dcs = alloc_dcookie(path);
133 if (!dcs) {
134 err = -ENOMEM;
135 goto out;
136 }
137 }
138
139 *cookie = dcookie_value(dcs);
140
141 out:
142 mutex_unlock(&dcookie_mutex);
143 return err;
144 }
145
146
147 /* And here is where the userspace process can look up the cookie value
148 * to retrieve the path.
149 */
do_lookup_dcookie(u64 cookie64,char __user * buf,size_t len)150 static int do_lookup_dcookie(u64 cookie64, char __user *buf, size_t len)
151 {
152 unsigned long cookie = (unsigned long)cookie64;
153 int err = -EINVAL;
154 char * kbuf;
155 char * path;
156 size_t pathlen;
157 struct dcookie_struct * dcs;
158
159 /* we could leak path information to users
160 * without dir read permission without this
161 */
162 if (!capable(CAP_SYS_ADMIN))
163 return -EPERM;
164
165 mutex_lock(&dcookie_mutex);
166
167 if (!is_live()) {
168 err = -EINVAL;
169 goto out;
170 }
171
172 if (!(dcs = find_dcookie(cookie)))
173 goto out;
174
175 err = -ENOMEM;
176 kbuf = kmalloc(PAGE_SIZE, GFP_KERNEL);
177 if (!kbuf)
178 goto out;
179
180 /* FIXME: (deleted) ? */
181 path = d_path(&dcs->path, kbuf, PAGE_SIZE);
182
183 mutex_unlock(&dcookie_mutex);
184
185 if (IS_ERR(path)) {
186 err = PTR_ERR(path);
187 goto out_free;
188 }
189
190 err = -ERANGE;
191
192 pathlen = kbuf + PAGE_SIZE - path;
193 if (pathlen <= len) {
194 err = pathlen;
195 if (copy_to_user(buf, path, pathlen))
196 err = -EFAULT;
197 }
198
199 out_free:
200 kfree(kbuf);
201 return err;
202 out:
203 mutex_unlock(&dcookie_mutex);
204 return err;
205 }
206
SYSCALL_DEFINE3(lookup_dcookie,u64,cookie64,char __user *,buf,size_t,len)207 SYSCALL_DEFINE3(lookup_dcookie, u64, cookie64, char __user *, buf, size_t, len)
208 {
209 return do_lookup_dcookie(cookie64, buf, len);
210 }
211
212 #ifdef CONFIG_COMPAT
COMPAT_SYSCALL_DEFINE4(lookup_dcookie,u32,w0,u32,w1,char __user *,buf,compat_size_t,len)213 COMPAT_SYSCALL_DEFINE4(lookup_dcookie, u32, w0, u32, w1, char __user *, buf, compat_size_t, len)
214 {
215 #ifdef __BIG_ENDIAN
216 return do_lookup_dcookie(((u64)w0 << 32) | w1, buf, len);
217 #else
218 return do_lookup_dcookie(((u64)w1 << 32) | w0, buf, len);
219 #endif
220 }
221 #endif
222
dcookie_init(void)223 static int dcookie_init(void)
224 {
225 struct list_head * d;
226 unsigned int i, hash_bits;
227 int err = -ENOMEM;
228
229 dcookie_cache = kmem_cache_create("dcookie_cache",
230 sizeof(struct dcookie_struct),
231 0, 0, NULL);
232
233 if (!dcookie_cache)
234 goto out;
235
236 dcookie_hashtable = kmalloc(PAGE_SIZE, GFP_KERNEL);
237 if (!dcookie_hashtable)
238 goto out_kmem;
239
240 err = 0;
241
242 /*
243 * Find the power-of-two list-heads that can fit into the allocation..
244 * We don't guarantee that "sizeof(struct list_head)" is necessarily
245 * a power-of-two.
246 */
247 hash_size = PAGE_SIZE / sizeof(struct list_head);
248 hash_bits = 0;
249 do {
250 hash_bits++;
251 } while ((hash_size >> hash_bits) != 0);
252 hash_bits--;
253
254 /*
255 * Re-calculate the actual number of entries and the mask
256 * from the number of bits we can fit.
257 */
258 hash_size = 1UL << hash_bits;
259
260 /* And initialize the newly allocated array */
261 d = dcookie_hashtable;
262 i = hash_size;
263 do {
264 INIT_LIST_HEAD(d);
265 d++;
266 i--;
267 } while (i);
268
269 out:
270 return err;
271 out_kmem:
272 kmem_cache_destroy(dcookie_cache);
273 goto out;
274 }
275
276
free_dcookie(struct dcookie_struct * dcs)277 static void free_dcookie(struct dcookie_struct * dcs)
278 {
279 struct dentry *d = dcs->path.dentry;
280
281 spin_lock(&d->d_lock);
282 d->d_flags &= ~DCACHE_COOKIE;
283 spin_unlock(&d->d_lock);
284
285 path_put(&dcs->path);
286 kmem_cache_free(dcookie_cache, dcs);
287 }
288
289
dcookie_exit(void)290 static void dcookie_exit(void)
291 {
292 struct list_head * list;
293 struct list_head * pos;
294 struct list_head * pos2;
295 struct dcookie_struct * dcs;
296 size_t i;
297
298 for (i = 0; i < hash_size; ++i) {
299 list = dcookie_hashtable + i;
300 list_for_each_safe(pos, pos2, list) {
301 dcs = list_entry(pos, struct dcookie_struct, hash_list);
302 list_del(&dcs->hash_list);
303 free_dcookie(dcs);
304 }
305 }
306
307 kfree(dcookie_hashtable);
308 kmem_cache_destroy(dcookie_cache);
309 }
310
311
312 struct dcookie_user {
313 struct list_head next;
314 };
315
dcookie_register(void)316 struct dcookie_user * dcookie_register(void)
317 {
318 struct dcookie_user * user;
319
320 mutex_lock(&dcookie_mutex);
321
322 user = kmalloc(sizeof(struct dcookie_user), GFP_KERNEL);
323 if (!user)
324 goto out;
325
326 if (!is_live() && dcookie_init())
327 goto out_free;
328
329 list_add(&user->next, &dcookie_users);
330
331 out:
332 mutex_unlock(&dcookie_mutex);
333 return user;
334 out_free:
335 kfree(user);
336 user = NULL;
337 goto out;
338 }
339
340
dcookie_unregister(struct dcookie_user * user)341 void dcookie_unregister(struct dcookie_user * user)
342 {
343 mutex_lock(&dcookie_mutex);
344
345 list_del(&user->next);
346 kfree(user);
347
348 if (!is_live())
349 dcookie_exit();
350
351 mutex_unlock(&dcookie_mutex);
352 }
353
354 EXPORT_SYMBOL_GPL(dcookie_register);
355 EXPORT_SYMBOL_GPL(dcookie_unregister);
356 EXPORT_SYMBOL_GPL(get_dcookie);
357