fs/afs/security.c

   1 // SPDX-License-Identifier: GPL-2.0-or-later
   2 /* AFS security handling
   3  *
   4  * Copyright (C) 2007, 2017 Red Hat, Inc. All Rights Reserved.
   5  * Written by David Howells (dhowells@redhat.com)
   6  */
   7
   8 #include <linux/init.h>
   9 #include <linux/slab.h>
  10 #include <linux/fs.h>
  11 #include <linux/ctype.h>
  12 #include <linux/sched.h>
  13 #include <linux/hashtable.h>
  14 #include <keys/rxrpc-type.h>
  15 #include "internal.h"
  16
  17 static DEFINE_HASHTABLE(afs_permits_cache, 10);
  18 static DEFINE_SPINLOCK(afs_permits_lock);
  19
  20 /*
  21  * get a key
  22  */
  23 struct key *afs_request_key(struct afs_cell *cell)
  24 {
  25         struct key *key;
  26
  27         _enter("{%x}", key_serial(cell->anonymous_key));
  28
  29         _debug("key %s", cell->anonymous_key->description);
  30         key = request_key(&key_type_rxrpc, cell->anonymous_key->description,
  31                           NULL, NULL);
  32         if (IS_ERR(key)) {
  33                 if (PTR_ERR(key) != -ENOKEY) {
  34                         _leave(" = %ld", PTR_ERR(key));
  35                         return key;
  36                 }
  37
  38                 /* act as anonymous user */
  39                 _leave(" = {%x} [anon]", key_serial(cell->anonymous_key));
  40                 return key_get(cell->anonymous_key);
  41         } else {
  42                 /* act as authorised user */
  43                 _leave(" = {%x} [auth]", key_serial(key));
  44                 return key;
  45         }
  46 }
  47
  48 /*
  49  * Dispose of a list of permits.
  50  */
  51 static void afs_permits_rcu(struct rcu_head *rcu)
  52 {
  53         struct afs_permits *permits =
  54                 container_of(rcu, struct afs_permits, rcu);
  55         int i;
  56
  57         for (i = 0; i < permits->nr_permits; i++)
  58                 key_put(permits->permits[i].key);
  59         kfree(permits);
  60 }
  61
  62 /*
  63  * Discard a permission cache.
  64  */
  65 void afs_put_permits(struct afs_permits *permits)
  66 {
  67         if (permits && refcount_dec_and_test(&permits->usage)) {
  68                 spin_lock(&afs_permits_lock);
  69                 hash_del_rcu(&permits->hash_node);
  70                 spin_unlock(&afs_permits_lock);
  71                 call_rcu(&permits->rcu, afs_permits_rcu);
  72         }
  73 }
  74
  75 /*
  76  * Clear a permit cache on callback break.
  77  */
  78 void afs_clear_permits(struct afs_vnode *vnode)
  79 {
  80         struct afs_permits *permits;
  81
  82         spin_lock(&vnode->lock);
  83         permits = rcu_dereference_protected(vnode->permit_cache,
  84                                             lockdep_is_held(&vnode->lock));
  85         RCU_INIT_POINTER(vnode->permit_cache, NULL);
  86         spin_unlock(&vnode->lock);
  87
  88         afs_put_permits(permits);
  89 }
  90
  91 /*
  92  * Hash a list of permits.  Use simple addition to make it easy to add an extra
  93  * one at an as-yet indeterminate position in the list.
  94  */
  95 static void afs_hash_permits(struct afs_permits *permits)
  96 {
  97         unsigned long h = permits->nr_permits;
  98         int i;
  99
 100         for (i = 0; i < permits->nr_permits; i++) {
 101                 h += (unsigned long)permits->permits[i].key / sizeof(void *);
 102                 h += permits->permits[i].access;
 103         }
 104
 105         permits->h = h;
 106 }
 107
 108 /*
 109  * Cache the CallerAccess result obtained from doing a fileserver operation
 110  * that returned a vnode status for a particular key.  If a callback break
 111  * occurs whilst the operation was in progress then we have to ditch the cache
 112  * as the ACL *may* have changed.
 113  */
 114 void afs_cache_permit(struct afs_vnode *vnode, struct key *key,
 115                       unsigned int cb_break, struct afs_status_cb *scb)
 116 {
 117         struct afs_permits *permits, *xpermits, *replacement, *zap, *new = NULL;
 118         afs_access_t caller_access = scb->status.caller_access;
 119         size_t size = 0;
 120         bool changed = false;
 121         int i, j;
 122
 123         _enter("{%llx:%llu},%x,%x",
 124                vnode->fid.vid, vnode->fid.vnode, key_serial(key), caller_access);
 125
 126         rcu_read_lock();
 127
 128         /* Check for the common case first: We got back the same access as last
 129          * time we tried and already have it recorded.
 130          */
 131         permits = rcu_dereference(vnode->permit_cache);
 132         if (permits) {
 133                 if (!permits->invalidated) {
 134                         for (i = 0; i < permits->nr_permits; i++) {
 135                                 if (permits->permits[i].key < key)
 136                                         continue;
 137                                 if (permits->permits[i].key > key)
 138                                         break;
 139                                 if (permits->permits[i].access != caller_access) {
 140                                         changed = true;
 141                                         break;
 142                                 }
 143
 144                                 if (afs_cb_is_broken(cb_break, vnode,
 145                                                      rcu_dereference(vnode->cb_interest))) {
 146                                         changed = true;
 147                                         break;
 148                                 }
 149
 150                                 /* The cache is still good. */
 151                                 rcu_read_unlock();
 152                                 return;
 153                         }
 154                 }
 155
 156                 changed |= permits->invalidated;
 157                 size = permits->nr_permits;
 158
 159                 /* If this set of permits is now wrong, clear the permits
 160                  * pointer so that no one tries to use the stale information.
 161                  */
 162                 if (changed) {
 163                         spin_lock(&vnode->lock);
 164                         if (permits != rcu_access_pointer(vnode->permit_cache))
 165                                 goto someone_else_changed_it_unlock;
 166                         RCU_INIT_POINTER(vnode->permit_cache, NULL);
 167                         spin_unlock(&vnode->lock);
 168
 169                         afs_put_permits(permits);
 170                         permits = NULL;
 171                         size = 0;
 172                 }
 173         }
 174
 175         if (afs_cb_is_broken(cb_break, vnode, rcu_dereference(vnode->cb_interest)))
 176                 goto someone_else_changed_it;
 177
 178         /* We need a ref on any permits list we want to copy as we'll have to
 179          * drop the lock to do memory allocation.
 180          */
 181         if (permits && !refcount_inc_not_zero(&permits->usage))
 182                 goto someone_else_changed_it;
 183
 184         rcu_read_unlock();
 185
 186         /* Speculatively create a new list with the revised permission set.  We
 187          * discard this if we find an extant match already in the hash, but
 188          * it's easier to compare with memcmp this way.
 189          *
 190          * We fill in the key pointers at this time, but we don't get the refs
 191          * yet.
 192          */
 193         size++;
 194         new = kzalloc(sizeof(struct afs_permits) +
 195                       sizeof(struct afs_permit) * size, GFP_NOFS);
 196         if (!new)
 197                 goto out_put;
 198
 199         refcount_set(&new->usage, 1);
 200         new->nr_permits = size;
 201         i = j = 0;
 202         if (permits) {
 203                 for (i = 0; i < permits->nr_permits; i++) {
 204                         if (j == i && permits->permits[i].key > key) {
 205                                 new->permits[j].key = key;
 206                                 new->permits[j].access = caller_access;
 207                                 j++;
 208                         }
 209                         new->permits[j].key = permits->permits[i].key;
 210                         new->permits[j].access = permits->permits[i].access;
 211                         j++;
 212                 }
 213         }
 214
 215         if (j == i) {
 216                 new->permits[j].key = key;
 217                 new->permits[j].access = caller_access;
 218         }
 219
 220         afs_hash_permits(new);
 221
 222         /* Now see if the permit list we want is actually already available */
 223         spin_lock(&afs_permits_lock);
 224
 225         hash_for_each_possible(afs_permits_cache, xpermits, hash_node, new->h) {
 226                 if (xpermits->h != new->h ||
 227                     xpermits->invalidated ||
 228                     xpermits->nr_permits != new->nr_permits ||
 229                     memcmp(xpermits->permits, new->permits,
 230                            new->nr_permits * sizeof(struct afs_permit)) != 0)
 231                         continue;
 232
 233                 if (refcount_inc_not_zero(&xpermits->usage)) {
 234                         replacement = xpermits;
 235                         goto found;
 236                 }
 237
 238                 break;
 239         }
 240
 241         for (i = 0; i < new->nr_permits; i++)
 242                 key_get(new->permits[i].key);
 243         hash_add_rcu(afs_permits_cache, &new->hash_node, new->h);
 244         replacement = new;
 245         new = NULL;
 246
 247 found:
 248         spin_unlock(&afs_permits_lock);
 249
 250         kfree(new);
 251
 252         rcu_read_lock();
 253         spin_lock(&vnode->lock);
 254         zap = rcu_access_pointer(vnode->permit_cache);
 255         if (!afs_cb_is_broken(cb_break, vnode, rcu_dereference(vnode->cb_interest)) &&
 256             zap == permits)
 257                 rcu_assign_pointer(vnode->permit_cache, replacement);
 258         else
 259                 zap = replacement;
 260         spin_unlock(&vnode->lock);
 261         rcu_read_unlock();
 262         afs_put_permits(zap);
 263 out_put:
 264         afs_put_permits(permits);
 265         return;
 266
 267 someone_else_changed_it_unlock:
 268         spin_unlock(&vnode->lock);
 269 someone_else_changed_it:
 270         /* Someone else changed the cache under us - don't recheck at this
 271          * time.
 272          */
 273         rcu_read_unlock();
 274         return;
 275 }
 276
 277 /*
 278  * check with the fileserver to see if the directory or parent directory is
 279  * permitted to be accessed with this authorisation, and if so, what access it
 280  * is granted
 281  */
 282 int afs_check_permit(struct afs_vnode *vnode, struct key *key,
 283                      afs_access_t *_access)
 284 {
 285         struct afs_permits *permits;
 286         bool valid = false;
 287         int i, ret;
 288
 289         _enter("{%llx:%llu},%x",
 290                vnode->fid.vid, vnode->fid.vnode, key_serial(key));
 291
 292         /* check the permits to see if we've got one yet */
 293         if (key == vnode->volume->cell->anonymous_key) {
 294                 _debug("anon");
 295                 *_access = vnode->status.anon_access;
 296                 valid = true;
 297         } else {
 298                 rcu_read_lock();
 299                 permits = rcu_dereference(vnode->permit_cache);
 300                 if (permits) {
 301                         for (i = 0; i < permits->nr_permits; i++) {
 302                                 if (permits->permits[i].key < key)
 303                                         continue;
 304                                 if (permits->permits[i].key > key)
 305                                         break;
 306
 307                                 *_access = permits->permits[i].access;
 308                                 valid = !permits->invalidated;
 309                                 break;
 310                         }
 311                 }
 312                 rcu_read_unlock();
 313         }
 314
 315         if (!valid) {
 316                 /* Check the status on the file we're actually interested in
 317                  * (the post-processing will cache the result).
 318                  */
 319                 _debug("no valid permit");
 320
 321                 ret = afs_fetch_status(vnode, key, false, _access);
 322                 if (ret < 0) {
 323                         *_access = 0;
 324                         _leave(" = %d", ret);
 325                         return ret;
 326                 }
 327         }
 328
 329         _leave(" = 0 [access %x]", *_access);
 330         return 0;
 331 }
 332
 333 /*
 334  * check the permissions on an AFS file
 335  * - AFS ACLs are attached to directories only, and a file is controlled by its
 336  *   parent directory's ACL
 337  */
 338 int afs_permission(struct inode *inode, int mask)
 339 {
 340         struct afs_vnode *vnode = AFS_FS_I(inode);
 341         afs_access_t uninitialized_var(access);
 342         struct key *key;
 343         int ret;
 344
 345         if (mask & MAY_NOT_BLOCK)
 346                 return -ECHILD;
 347
 348         _enter("{{%llx:%llu},%lx},%x,",
 349                vnode->fid.vid, vnode->fid.vnode, vnode->flags, mask);
 350
 351         key = afs_request_key(vnode->volume->cell);
 352         if (IS_ERR(key)) {
 353                 _leave(" = %ld [key]", PTR_ERR(key));
 354                 return PTR_ERR(key);
 355         }
 356
 357         ret = afs_validate(vnode, key);
 358         if (ret < 0)
 359                 goto error;
 360
 361         /* check the permits to see if we've got one yet */
 362         ret = afs_check_permit(vnode, key, &access);
 363         if (ret < 0)
 364                 goto error;
 365
 366         /* interpret the access mask */
 367         _debug("REQ %x ACC %x on %s",
 368                mask, access, S_ISDIR(inode->i_mode) ? "dir" : "file");
 369
 370         if (S_ISDIR(inode->i_mode)) {
 371                 if (mask & (MAY_EXEC | MAY_READ | MAY_CHDIR)) {
 372                         if (!(access & AFS_ACE_LOOKUP))
 373                                 goto permission_denied;
 374                 }
 375                 if (mask & MAY_WRITE) {
 376                         if (!(access & (AFS_ACE_DELETE | /* rmdir, unlink, rename from */
 377                                         AFS_ACE_INSERT))) /* create, mkdir, symlink, rename to */
 378                                 goto permission_denied;
 379                 }
 380         } else {
 381                 if (!(access & AFS_ACE_LOOKUP))
 382                         goto permission_denied;
 383                 if ((mask & MAY_EXEC) && !(inode->i_mode & S_IXUSR))
 384                         goto permission_denied;
 385                 if (mask & (MAY_EXEC | MAY_READ)) {
 386                         if (!(access & AFS_ACE_READ))
 387                                 goto permission_denied;
 388                         if (!(inode->i_mode & S_IRUSR))
 389                                 goto permission_denied;
 390                 } else if (mask & MAY_WRITE) {
 391                         if (!(access & AFS_ACE_WRITE))
 392                                 goto permission_denied;
 393                         if (!(inode->i_mode & S_IWUSR))
 394                                 goto permission_denied;
 395                 }
 396         }
 397
 398         key_put(key);
 399         _leave(" = %d", ret);
 400         return ret;
 401
 402 permission_denied:
 403         ret = -EACCES;
 404 error:
 405         key_put(key);
 406         _leave(" = %d", ret);
 407         return ret;
 408 }
 409
 410 void __exit afs_clean_up_permit_cache(void)
 411 {
 412         int i;
 413
 414         for (i = 0; i < HASH_SIZE(afs_permits_cache); i++)
 415                 WARN_ON_ONCE(!hlist_empty(&afs_permits_cache[i]));
 416
 417 }