fs/dcookies.c

   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
  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 */
  54 static inline unsigned long dcookie_value(struct dcookie_struct * dcs)
  55 {
  56         return (unsigned long)dcs->path.dentry;
  57 }
  58
  59
  60 static size_t dcookie_hash(unsigned long dcookie)
  61 {
  62         return (dcookie >> L1_CACHE_SHIFT) & (hash_size - 1);
  63 }
  64
  65
  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
  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
  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  */
 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  */
 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
 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
 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
 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
 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
 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
 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
 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);