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 <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);