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/config.h>
  16 #include <linux/syscalls.h>
  17 #include <linux/module.h>
  18 #include <linux/slab.h>
  19 #include <linux/list.h>
  20 #include <linux/mount.h>
  21 #include <linux/dcache.h>
  22 #include <linux/mm.h>
  23 #include <linux/errno.h>
  24 #include <linux/dcookies.h>
  25 #include <asm/uaccess.h>
  26
  27 /* The dcookies are allocated from a kmem_cache and
  28  * hashed onto a small number of lists. None of the
  29  * code here is particularly performance critical
  30  */
  31 struct dcookie_struct {
  32         struct dentry * dentry;
  33         struct vfsmount * vfsmnt;
  34         struct list_head hash_list;
  35 };
  36
  37 static LIST_HEAD(dcookie_users);
  38 static DECLARE_MUTEX(dcookie_sem);
  39 static kmem_cache_t * dcookie_cache;
  40 static struct list_head * dcookie_hashtable;
  41 static size_t hash_size;
  42
  43 static inline int is_live(void)
  44 {
  45         return !(list_empty(&dcookie_users));
  46 }
  47
  48
  49 /* The dentry is locked, its address will do for the cookie */
  50 static inline unsigned long dcookie_value(struct dcookie_struct * dcs)
  51 {
  52         return (unsigned long)dcs->dentry;
  53 }
  54
  55
  56 static size_t dcookie_hash(unsigned long dcookie)
  57 {
  58         return (dcookie >> L1_CACHE_SHIFT) & (hash_size - 1);
  59 }
  60
  61
  62 static struct dcookie_struct * find_dcookie(unsigned long dcookie)
  63 {
  64         struct dcookie_struct *found = NULL;
  65         struct dcookie_struct * dcs;
  66         struct list_head * pos;
  67         struct list_head * list;
  68
  69         list = dcookie_hashtable + dcookie_hash(dcookie);
  70
  71         list_for_each(pos, list) {
  72                 dcs = list_entry(pos, struct dcookie_struct, hash_list);
  73                 if (dcookie_value(dcs) == dcookie) {
  74                         found = dcs;
  75                         break;
  76                 }
  77         }
  78
  79         return found;
  80 }
  81
  82
  83 static void hash_dcookie(struct dcookie_struct * dcs)
  84 {
  85         struct list_head * list = dcookie_hashtable + dcookie_hash(dcookie_value(dcs));
  86         list_add(&dcs->hash_list, list);
  87 }
  88
  89
  90 static struct dcookie_struct * alloc_dcookie(struct dentry * dentry,
  91         struct vfsmount * vfsmnt)
  92 {
  93         struct dcookie_struct * dcs = kmem_cache_alloc(dcookie_cache, GFP_KERNEL);
  94         if (!dcs)
  95                 return NULL;
  96
  97         atomic_inc(&dentry->d_count);
  98         atomic_inc(&vfsmnt->mnt_count);
  99         dentry->d_cookie = dcs;
 100
 101         dcs->dentry = dentry;
 102         dcs->vfsmnt = vfsmnt;
 103         hash_dcookie(dcs);
 104
 105         return dcs;
 106 }
 107
 108
 109 /* This is the main kernel-side routine that retrieves the cookie
 110  * value for a dentry/vfsmnt pair.
 111  */
 112 int get_dcookie(struct dentry * dentry, struct vfsmount * vfsmnt,
 113         unsigned long * cookie)
 114 {
 115         int err = 0;
 116         struct dcookie_struct * dcs;
 117
 118         down(&dcookie_sem);
 119
 120         if (!is_live()) {
 121                 err = -EINVAL;
 122                 goto out;
 123         }
 124
 125         dcs = dentry->d_cookie;
 126
 127         if (!dcs)
 128                 dcs = alloc_dcookie(dentry, vfsmnt);
 129
 130         if (!dcs) {
 131                 err = -ENOMEM;
 132                 goto out;
 133         }
 134
 135         *cookie = dcookie_value(dcs);
 136
 137 out:
 138         up(&dcookie_sem);
 139         return err;
 140 }
 141
 142
 143 /* And here is where the userspace process can look up the cookie value
 144  * to retrieve the path.
 145  */
 146 asmlinkage long sys_lookup_dcookie(u64 cookie64, char __user * buf, size_t len)
 147 {
 148         unsigned long cookie = (unsigned long)cookie64;
 149         int err = -EINVAL;
 150         char * kbuf;
 151         char * path;
 152         size_t pathlen;
 153         struct dcookie_struct * dcs;
 154
 155         /* we could leak path information to users
 156          * without dir read permission without this
 157          */
 158         if (!capable(CAP_SYS_ADMIN))
 159                 return -EPERM;
 160
 161         down(&dcookie_sem);
 162
 163         if (!is_live()) {
 164                 err = -EINVAL;
 165                 goto out;
 166         }
 167
 168         if (!(dcs = find_dcookie(cookie)))
 169                 goto out;
 170
 171         err = -ENOMEM;
 172         kbuf = kmalloc(PAGE_SIZE, GFP_KERNEL);
 173         if (!kbuf)
 174                 goto out;
 175
 176         /* FIXME: (deleted) ? */
 177         path = d_path(dcs->dentry, dcs->vfsmnt, kbuf, PAGE_SIZE);
 178
 179         if (IS_ERR(path)) {
 180                 err = PTR_ERR(path);
 181                 goto out_free;
 182         }
 183
 184         err = -ERANGE;
 185
 186         pathlen = kbuf + PAGE_SIZE - path;
 187         if (pathlen <= len) {
 188                 err = pathlen;
 189                 if (copy_to_user(buf, path, pathlen))
 190                         err = -EFAULT;
 191         }
 192
 193 out_free:
 194         kfree(kbuf);
 195 out:
 196         up(&dcookie_sem);
 197         return err;
 198 }
 199
 200
 201 static int dcookie_init(void)
 202 {
 203         struct list_head * d;
 204         unsigned int i, hash_bits;
 205         int err = -ENOMEM;
 206
 207         dcookie_cache = kmem_cache_create("dcookie_cache",
 208                 sizeof(struct dcookie_struct),
 209                 0, 0, NULL, NULL);
 210
 211         if (!dcookie_cache)
 212                 goto out;
 213
 214         dcookie_hashtable = kmalloc(PAGE_SIZE, GFP_KERNEL);
 215         if (!dcookie_hashtable)
 216                 goto out_kmem;
 217
 218         err = 0;
 219
 220         /*
 221          * Find the power-of-two list-heads that can fit into the allocation..
 222          * We don't guarantee that "sizeof(struct list_head)" is necessarily
 223          * a power-of-two.
 224          */
 225         hash_size = PAGE_SIZE / sizeof(struct list_head);
 226         hash_bits = 0;
 227         do {
 228                 hash_bits++;
 229         } while ((hash_size >> hash_bits) != 0);
 230         hash_bits--;
 231
 232         /*
 233          * Re-calculate the actual number of entries and the mask
 234          * from the number of bits we can fit.
 235          */
 236         hash_size = 1UL << hash_bits;
 237
 238         /* And initialize the newly allocated array */
 239         d = dcookie_hashtable;
 240         i = hash_size;
 241         do {
 242                 INIT_LIST_HEAD(d);
 243                 d++;
 244                 i--;
 245         } while (i);
 246
 247 out:
 248         return err;
 249 out_kmem:
 250         kmem_cache_destroy(dcookie_cache);
 251         goto out;
 252 }
 253
 254
 255 static void free_dcookie(struct dcookie_struct * dcs)
 256 {
 257         dcs->dentry->d_cookie = NULL;
 258         dput(dcs->dentry);
 259         mntput(dcs->vfsmnt);
 260         kmem_cache_free(dcookie_cache, dcs);
 261 }
 262
 263
 264 static void dcookie_exit(void)
 265 {
 266         struct list_head * list;
 267         struct list_head * pos;
 268         struct list_head * pos2;
 269         struct dcookie_struct * dcs;
 270         size_t i;
 271
 272         for (i = 0; i < hash_size; ++i) {
 273                 list = dcookie_hashtable + i;
 274                 list_for_each_safe(pos, pos2, list) {
 275                         dcs = list_entry(pos, struct dcookie_struct, hash_list);
 276                         list_del(&dcs->hash_list);
 277                         free_dcookie(dcs);
 278                 }
 279         }
 280
 281         kfree(dcookie_hashtable);
 282         kmem_cache_destroy(dcookie_cache);
 283 }
 284
 285
 286 struct dcookie_user {
 287         struct list_head next;
 288 };
 289
 290 struct dcookie_user * dcookie_register(void)
 291 {
 292         struct dcookie_user * user;
 293
 294         down(&dcookie_sem);
 295
 296         user = kmalloc(sizeof(struct dcookie_user), GFP_KERNEL);
 297         if (!user)
 298                 goto out;
 299
 300         if (!is_live() && dcookie_init())
 301                 goto out_free;
 302
 303         list_add(&user->next, &dcookie_users);
 304
 305 out:
 306         up(&dcookie_sem);
 307         return user;
 308 out_free:
 309         kfree(user);
 310         user = NULL;
 311         goto out;
 312 }
 313
 314
 315 void dcookie_unregister(struct dcookie_user * user)
 316 {
 317         down(&dcookie_sem);
 318
 319         list_del(&user->next);
 320         kfree(user);
 321
 322         if (!is_live())
 323                 dcookie_exit();
 324
 325         up(&dcookie_sem);
 326 }
 327
 328 EXPORT_SYMBOL_GPL(dcookie_register);
 329 EXPORT_SYMBOL_GPL(dcookie_unregister);
 330 EXPORT_SYMBOL_GPL(get_dcookie);