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