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