fs/dcookies.c

   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 <linux/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(const 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(const 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, compat_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);