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/module.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 asmlinkage long sys_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         if (IS_ERR(path)) {
 182                 err = PTR_ERR(path);
 183                 goto out_free;
 184         }
 185
 186         err = -ERANGE;
 187
 188         pathlen = kbuf + PAGE_SIZE - path;
 189         if (pathlen <= len) {
 190                 err = pathlen;
 191                 if (copy_to_user(buf, path, pathlen))
 192                         err = -EFAULT;
 193         }
 194
 195 out_free:
 196         kfree(kbuf);
 197 out:
 198         mutex_unlock(&dcookie_mutex);
 199         return err;
 200 }
 201
 202
 203 static int dcookie_init(void)
 204 {
 205         struct list_head * d;
 206         unsigned int i, hash_bits;
 207         int err = -ENOMEM;
 208
 209         dcookie_cache = kmem_cache_create("dcookie_cache",
 210                 sizeof(struct dcookie_struct),
 211                 0, 0, NULL);
 212
 213         if (!dcookie_cache)
 214                 goto out;
 215
 216         dcookie_hashtable = kmalloc(PAGE_SIZE, GFP_KERNEL);
 217         if (!dcookie_hashtable)
 218                 goto out_kmem;
 219
 220         err = 0;
 221
 222         /*
 223          * Find the power-of-two list-heads that can fit into the allocation..
 224          * We don't guarantee that "sizeof(struct list_head)" is necessarily
 225          * a power-of-two.
 226          */
 227         hash_size = PAGE_SIZE / sizeof(struct list_head);
 228         hash_bits = 0;
 229         do {
 230                 hash_bits++;
 231         } while ((hash_size >> hash_bits) != 0);
 232         hash_bits--;
 233
 234         /*
 235          * Re-calculate the actual number of entries and the mask
 236          * from the number of bits we can fit.
 237          */
 238         hash_size = 1UL << hash_bits;
 239
 240         /* And initialize the newly allocated array */
 241         d = dcookie_hashtable;
 242         i = hash_size;
 243         do {
 244                 INIT_LIST_HEAD(d);
 245                 d++;
 246                 i--;
 247         } while (i);
 248
 249 out:
 250         return err;
 251 out_kmem:
 252         kmem_cache_destroy(dcookie_cache);
 253         goto out;
 254 }
 255
 256
 257 static void free_dcookie(struct dcookie_struct * dcs)
 258 {
 259         struct dentry *d = dcs->path.dentry;
 260
 261         spin_lock(&d->d_lock);
 262         d->d_flags &= ~DCACHE_COOKIE;
 263         spin_unlock(&d->d_lock);
 264
 265         path_put(&dcs->path);
 266         kmem_cache_free(dcookie_cache, dcs);
 267 }
 268
 269
 270 static void dcookie_exit(void)
 271 {
 272         struct list_head * list;
 273         struct list_head * pos;
 274         struct list_head * pos2;
 275         struct dcookie_struct * dcs;
 276         size_t i;
 277
 278         for (i = 0; i < hash_size; ++i) {
 279                 list = dcookie_hashtable + i;
 280                 list_for_each_safe(pos, pos2, list) {
 281                         dcs = list_entry(pos, struct dcookie_struct, hash_list);
 282                         list_del(&dcs->hash_list);
 283                         free_dcookie(dcs);
 284                 }
 285         }
 286
 287         kfree(dcookie_hashtable);
 288         kmem_cache_destroy(dcookie_cache);
 289 }
 290
 291
 292 struct dcookie_user {
 293         struct list_head next;
 294 };
 295
 296 struct dcookie_user * dcookie_register(void)
 297 {
 298         struct dcookie_user * user;
 299
 300         mutex_lock(&dcookie_mutex);
 301
 302         user = kmalloc(sizeof(struct dcookie_user), GFP_KERNEL);
 303         if (!user)
 304                 goto out;
 305
 306         if (!is_live() && dcookie_init())
 307                 goto out_free;
 308
 309         list_add(&user->next, &dcookie_users);
 310
 311 out:
 312         mutex_unlock(&dcookie_mutex);
 313         return user;
 314 out_free:
 315         kfree(user);
 316         user = NULL;
 317         goto out;
 318 }
 319
 320
 321 void dcookie_unregister(struct dcookie_user * user)
 322 {
 323         mutex_lock(&dcookie_mutex);
 324
 325         list_del(&user->next);
 326         kfree(user);
 327
 328         if (!is_live())
 329                 dcookie_exit();
 330
 331         mutex_unlock(&dcookie_mutex);
 332 }
 333
 334 EXPORT_SYMBOL_GPL(dcookie_register);
 335 EXPORT_SYMBOL_GPL(dcookie_unregister);
 336 EXPORT_SYMBOL_GPL(get_dcookie);