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         if (!dcs)
  97                 return NULL;
  98
  99         path->dentry->d_cookie = dcs;
 100         dcs->path = *path;
 101         path_get(path);
 102         hash_dcookie(dcs);
 103         return dcs;
 104 }
 105
 106
 107 /* This is the main kernel-side routine that retrieves the cookie
 108  * value for a dentry/vfsmnt pair.
 109  */
 110 int get_dcookie(struct path *path, unsigned long *cookie)
 111 {
 112         int err = 0;
 113         struct dcookie_struct * dcs;
 114
 115         mutex_lock(&dcookie_mutex);
 116
 117         if (!is_live()) {
 118                 err = -EINVAL;
 119                 goto out;
 120         }
 121
 122         dcs = path->dentry->d_cookie;
 123
 124         if (!dcs)
 125                 dcs = alloc_dcookie(path);
 126
 127         if (!dcs) {
 128                 err = -ENOMEM;
 129                 goto out;
 130         }
 131
 132         *cookie = dcookie_value(dcs);
 133
 134 out:
 135         mutex_unlock(&dcookie_mutex);
 136         return err;
 137 }
 138
 139
 140 /* And here is where the userspace process can look up the cookie value
 141  * to retrieve the path.
 142  */
 143 SYSCALL_DEFINE(lookup_dcookie)(u64 cookie64, char __user * buf, size_t len)
 144 {
 145         unsigned long cookie = (unsigned long)cookie64;
 146         int err = -EINVAL;
 147         char * kbuf;
 148         char * path;
 149         size_t pathlen;
 150         struct dcookie_struct * dcs;
 151
 152         /* we could leak path information to users
 153          * without dir read permission without this
 154          */
 155         if (!capable(CAP_SYS_ADMIN))
 156                 return -EPERM;
 157
 158         mutex_lock(&dcookie_mutex);
 159
 160         if (!is_live()) {
 161                 err = -EINVAL;
 162                 goto out;
 163         }
 164
 165         if (!(dcs = find_dcookie(cookie)))
 166                 goto out;
 167
 168         err = -ENOMEM;
 169         kbuf = kmalloc(PAGE_SIZE, GFP_KERNEL);
 170         if (!kbuf)
 171                 goto out;
 172
 173         /* FIXME: (deleted) ? */
 174         path = d_path(&dcs->path, kbuf, PAGE_SIZE);
 175
 176         if (IS_ERR(path)) {
 177                 err = PTR_ERR(path);
 178                 goto out_free;
 179         }
 180
 181         err = -ERANGE;
 182
 183         pathlen = kbuf + PAGE_SIZE - path;
 184         if (pathlen <= len) {
 185                 err = pathlen;
 186                 if (copy_to_user(buf, path, pathlen))
 187                         err = -EFAULT;
 188         }
 189
 190 out_free:
 191         kfree(kbuf);
 192 out:
 193         mutex_unlock(&dcookie_mutex);
 194         return err;
 195 }
 196 #ifdef CONFIG_HAVE_SYSCALL_WRAPPERS
 197 asmlinkage long SyS_lookup_dcookie(u64 cookie64, long buf, long len)
 198 {
 199         return SYSC_lookup_dcookie(cookie64, (char __user *) buf, (size_t) len);
 200 }
 201 SYSCALL_ALIAS(sys_lookup_dcookie, SyS_lookup_dcookie);
 202 #endif
 203
 204 static int dcookie_init(void)
 205 {
 206         struct list_head * d;
 207         unsigned int i, hash_bits;
 208         int err = -ENOMEM;
 209
 210         dcookie_cache = kmem_cache_create("dcookie_cache",
 211                 sizeof(struct dcookie_struct),
 212                 0, 0, NULL);
 213
 214         if (!dcookie_cache)
 215                 goto out;
 216
 217         dcookie_hashtable = kmalloc(PAGE_SIZE, GFP_KERNEL);
 218         if (!dcookie_hashtable)
 219                 goto out_kmem;
 220
 221         err = 0;
 222
 223         /*
 224          * Find the power-of-two list-heads that can fit into the allocation..
 225          * We don't guarantee that "sizeof(struct list_head)" is necessarily
 226          * a power-of-two.
 227          */
 228         hash_size = PAGE_SIZE / sizeof(struct list_head);
 229         hash_bits = 0;
 230         do {
 231                 hash_bits++;
 232         } while ((hash_size >> hash_bits) != 0);
 233         hash_bits--;
 234
 235         /*
 236          * Re-calculate the actual number of entries and the mask
 237          * from the number of bits we can fit.
 238          */
 239         hash_size = 1UL << hash_bits;
 240
 241         /* And initialize the newly allocated array */
 242         d = dcookie_hashtable;
 243         i = hash_size;
 244         do {
 245                 INIT_LIST_HEAD(d);
 246                 d++;
 247                 i--;
 248         } while (i);
 249
 250 out:
 251         return err;
 252 out_kmem:
 253         kmem_cache_destroy(dcookie_cache);
 254         goto out;
 255 }
 256
 257
 258 static void free_dcookie(struct dcookie_struct * dcs)
 259 {
 260         dcs->path.dentry->d_cookie = NULL;
 261         path_put(&dcs->path);
 262         kmem_cache_free(dcookie_cache, dcs);
 263 }
 264
 265
 266 static void dcookie_exit(void)
 267 {
 268         struct list_head * list;
 269         struct list_head * pos;
 270         struct list_head * pos2;
 271         struct dcookie_struct * dcs;
 272         size_t i;
 273
 274         for (i = 0; i < hash_size; ++i) {
 275                 list = dcookie_hashtable + i;
 276                 list_for_each_safe(pos, pos2, list) {
 277                         dcs = list_entry(pos, struct dcookie_struct, hash_list);
 278                         list_del(&dcs->hash_list);
 279                         free_dcookie(dcs);
 280                 }
 281         }
 282
 283         kfree(dcookie_hashtable);
 284         kmem_cache_destroy(dcookie_cache);
 285 }
 286
 287
 288 struct dcookie_user {
 289         struct list_head next;
 290 };
 291
 292 struct dcookie_user * dcookie_register(void)
 293 {
 294         struct dcookie_user * user;
 295
 296         mutex_lock(&dcookie_mutex);
 297
 298         user = kmalloc(sizeof(struct dcookie_user), GFP_KERNEL);
 299         if (!user)
 300                 goto out;
 301
 302         if (!is_live() && dcookie_init())
 303                 goto out_free;
 304
 305         list_add(&user->next, &dcookie_users);
 306
 307 out:
 308         mutex_unlock(&dcookie_mutex);
 309         return user;
 310 out_free:
 311         kfree(user);
 312         user = NULL;
 313         goto out;
 314 }
 315
 316
 317 void dcookie_unregister(struct dcookie_user * user)
 318 {
 319         mutex_lock(&dcookie_mutex);
 320
 321         list_del(&user->next);
 322         kfree(user);
 323
 324         if (!is_live())
 325                 dcookie_exit();
 326
 327         mutex_unlock(&dcookie_mutex);
 328 }
 329
 330 EXPORT_SYMBOL_GPL(dcookie_register);
 331 EXPORT_SYMBOL_GPL(dcookie_unregister);
 332 EXPORT_SYMBOL_GPL(get_dcookie);