linux/fs/afs/security.c
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   1/* AFS security handling
   2 *
   3 * Copyright (C) 2007 Red Hat, Inc. All Rights Reserved.
   4 * Written by David Howells (dhowells@redhat.com)
   5 *
   6 * This program is free software; you can redistribute it and/or
   7 * modify it under the terms of the GNU General Public License
   8 * as published by the Free Software Foundation; either version
   9 * 2 of the License, or (at your option) any later version.
  10 */
  11
  12#include <linux/init.h>
  13#include <linux/slab.h>
  14#include <linux/fs.h>
  15#include <linux/ctype.h>
  16#include <linux/sched.h>
  17#include <keys/rxrpc-type.h>
  18#include "internal.h"
  19
  20/*
  21 * get a key
  22 */
  23struct 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);
  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 permits list
  50 */
  51void afs_zap_permits(struct rcu_head *rcu)
  52{
  53        struct afs_permits *permits =
  54                container_of(rcu, struct afs_permits, rcu);
  55        int loop;
  56
  57        _enter("{%d}", permits->count);
  58
  59        for (loop = permits->count - 1; loop >= 0; loop--)
  60                key_put(permits->permits[loop].key);
  61        kfree(permits);
  62}
  63
  64/*
  65 * dispose of a permits list in which all the key pointers have been copied
  66 */
  67static void afs_dispose_of_permits(struct rcu_head *rcu)
  68{
  69        struct afs_permits *permits =
  70                container_of(rcu, struct afs_permits, rcu);
  71
  72        _enter("{%d}", permits->count);
  73
  74        kfree(permits);
  75}
  76
  77/*
  78 * get the authorising vnode - this is the specified inode itself if it's a
  79 * directory or it's the parent directory if the specified inode is a file or
  80 * symlink
  81 * - the caller must release the ref on the inode
  82 */
  83static struct afs_vnode *afs_get_auth_inode(struct afs_vnode *vnode,
  84                                            struct key *key)
  85{
  86        struct afs_vnode *auth_vnode;
  87        struct inode *auth_inode;
  88
  89        _enter("");
  90
  91        if (S_ISDIR(vnode->vfs_inode.i_mode)) {
  92                auth_inode = igrab(&vnode->vfs_inode);
  93                ASSERT(auth_inode != NULL);
  94        } else {
  95                auth_inode = afs_iget(vnode->vfs_inode.i_sb, key,
  96                                      &vnode->status.parent, NULL, NULL);
  97                if (IS_ERR(auth_inode))
  98                        return ERR_CAST(auth_inode);
  99        }
 100
 101        auth_vnode = AFS_FS_I(auth_inode);
 102        _leave(" = {%x}", auth_vnode->fid.vnode);
 103        return auth_vnode;
 104}
 105
 106/*
 107 * clear the permit cache on a directory vnode
 108 */
 109void afs_clear_permits(struct afs_vnode *vnode)
 110{
 111        struct afs_permits *permits;
 112
 113        _enter("{%x:%u}", vnode->fid.vid, vnode->fid.vnode);
 114
 115        mutex_lock(&vnode->permits_lock);
 116        permits = vnode->permits;
 117        rcu_assign_pointer(vnode->permits, NULL);
 118        mutex_unlock(&vnode->permits_lock);
 119
 120        if (permits)
 121                call_rcu(&permits->rcu, afs_zap_permits);
 122        _leave("");
 123}
 124
 125/*
 126 * add the result obtained for a vnode to its or its parent directory's cache
 127 * for the key used to access it
 128 */
 129void afs_cache_permit(struct afs_vnode *vnode, struct key *key, long acl_order)
 130{
 131        struct afs_permits *permits, *xpermits;
 132        struct afs_permit *permit;
 133        struct afs_vnode *auth_vnode;
 134        int count, loop;
 135
 136        _enter("{%x:%u},%x,%lx",
 137               vnode->fid.vid, vnode->fid.vnode, key_serial(key), acl_order);
 138
 139        auth_vnode = afs_get_auth_inode(vnode, key);
 140        if (IS_ERR(auth_vnode)) {
 141                _leave(" [get error %ld]", PTR_ERR(auth_vnode));
 142                return;
 143        }
 144
 145        mutex_lock(&auth_vnode->permits_lock);
 146
 147        /* guard against a rename being detected whilst we waited for the
 148         * lock */
 149        if (memcmp(&auth_vnode->fid, &vnode->status.parent,
 150                   sizeof(struct afs_fid)) != 0) {
 151                _debug("renamed");
 152                goto out_unlock;
 153        }
 154
 155        /* have to be careful as the directory's callback may be broken between
 156         * us receiving the status we're trying to cache and us getting the
 157         * lock to update the cache for the status */
 158        if (auth_vnode->acl_order - acl_order > 0) {
 159                _debug("ACL changed?");
 160                goto out_unlock;
 161        }
 162
 163        /* always update the anonymous mask */
 164        _debug("anon access %x", vnode->status.anon_access);
 165        auth_vnode->status.anon_access = vnode->status.anon_access;
 166        if (key == vnode->volume->cell->anonymous_key)
 167                goto out_unlock;
 168
 169        xpermits = auth_vnode->permits;
 170        count = 0;
 171        if (xpermits) {
 172                /* see if the permit is already in the list
 173                 * - if it is then we just amend the list
 174                 */
 175                count = xpermits->count;
 176                permit = xpermits->permits;
 177                for (loop = count; loop > 0; loop--) {
 178                        if (permit->key == key) {
 179                                permit->access_mask =
 180                                        vnode->status.caller_access;
 181                                goto out_unlock;
 182                        }
 183                        permit++;
 184                }
 185        }
 186
 187        permits = kmalloc(sizeof(*permits) + sizeof(*permit) * (count + 1),
 188                          GFP_NOFS);
 189        if (!permits)
 190                goto out_unlock;
 191
 192        if (xpermits)
 193                memcpy(permits->permits, xpermits->permits,
 194                        count * sizeof(struct afs_permit));
 195
 196        _debug("key %x access %x",
 197               key_serial(key), vnode->status.caller_access);
 198        permits->permits[count].access_mask = vnode->status.caller_access;
 199        permits->permits[count].key = key_get(key);
 200        permits->count = count + 1;
 201
 202        rcu_assign_pointer(auth_vnode->permits, permits);
 203        if (xpermits)
 204                call_rcu(&xpermits->rcu, afs_dispose_of_permits);
 205
 206out_unlock:
 207        mutex_unlock(&auth_vnode->permits_lock);
 208        iput(&auth_vnode->vfs_inode);
 209        _leave("");
 210}
 211
 212/*
 213 * check with the fileserver to see if the directory or parent directory is
 214 * permitted to be accessed with this authorisation, and if so, what access it
 215 * is granted
 216 */
 217static int afs_check_permit(struct afs_vnode *vnode, struct key *key,
 218                            afs_access_t *_access)
 219{
 220        struct afs_permits *permits;
 221        struct afs_permit *permit;
 222        struct afs_vnode *auth_vnode;
 223        bool valid;
 224        int loop, ret;
 225
 226        _enter("{%x:%u},%x",
 227               vnode->fid.vid, vnode->fid.vnode, key_serial(key));
 228
 229        auth_vnode = afs_get_auth_inode(vnode, key);
 230        if (IS_ERR(auth_vnode)) {
 231                *_access = 0;
 232                _leave(" = %ld", PTR_ERR(auth_vnode));
 233                return PTR_ERR(auth_vnode);
 234        }
 235
 236        ASSERT(S_ISDIR(auth_vnode->vfs_inode.i_mode));
 237
 238        /* check the permits to see if we've got one yet */
 239        if (key == auth_vnode->volume->cell->anonymous_key) {
 240                _debug("anon");
 241                *_access = auth_vnode->status.anon_access;
 242                valid = true;
 243        } else {
 244                valid = false;
 245                rcu_read_lock();
 246                permits = rcu_dereference(auth_vnode->permits);
 247                if (permits) {
 248                        permit = permits->permits;
 249                        for (loop = permits->count; loop > 0; loop--) {
 250                                if (permit->key == key) {
 251                                        _debug("found in cache");
 252                                        *_access = permit->access_mask;
 253                                        valid = true;
 254                                        break;
 255                                }
 256                                permit++;
 257                        }
 258                }
 259                rcu_read_unlock();
 260        }
 261
 262        if (!valid) {
 263                /* check the status on the file we're actually interested in
 264                 * (the post-processing will cache the result on auth_vnode) */
 265                _debug("no valid permit");
 266
 267                set_bit(AFS_VNODE_CB_BROKEN, &vnode->flags);
 268                ret = afs_vnode_fetch_status(vnode, auth_vnode, key);
 269                if (ret < 0) {
 270                        iput(&auth_vnode->vfs_inode);
 271                        *_access = 0;
 272                        _leave(" = %d", ret);
 273                        return ret;
 274                }
 275                *_access = vnode->status.caller_access;
 276        }
 277
 278        iput(&auth_vnode->vfs_inode);
 279        _leave(" = 0 [access %x]", *_access);
 280        return 0;
 281}
 282
 283/*
 284 * check the permissions on an AFS file
 285 * - AFS ACLs are attached to directories only, and a file is controlled by its
 286 *   parent directory's ACL
 287 */
 288int afs_permission(struct inode *inode, int mask)
 289{
 290        struct afs_vnode *vnode = AFS_FS_I(inode);
 291        afs_access_t uninitialized_var(access);
 292        struct key *key;
 293        int ret;
 294
 295        if (mask & MAY_NOT_BLOCK)
 296                return -ECHILD;
 297
 298        _enter("{{%x:%u},%lx},%x,",
 299               vnode->fid.vid, vnode->fid.vnode, vnode->flags, mask);
 300
 301        key = afs_request_key(vnode->volume->cell);
 302        if (IS_ERR(key)) {
 303                _leave(" = %ld [key]", PTR_ERR(key));
 304                return PTR_ERR(key);
 305        }
 306
 307        /* if the promise has expired, we need to check the server again */
 308        if (!vnode->cb_promised) {
 309                _debug("not promised");
 310                ret = afs_vnode_fetch_status(vnode, NULL, key);
 311                if (ret < 0)
 312                        goto error;
 313                _debug("new promise [fl=%lx]", vnode->flags);
 314        }
 315
 316        /* check the permits to see if we've got one yet */
 317        ret = afs_check_permit(vnode, key, &access);
 318        if (ret < 0)
 319                goto error;
 320
 321        /* interpret the access mask */
 322        _debug("REQ %x ACC %x on %s",
 323               mask, access, S_ISDIR(inode->i_mode) ? "dir" : "file");
 324
 325        if (S_ISDIR(inode->i_mode)) {
 326                if (mask & MAY_EXEC) {
 327                        if (!(access & AFS_ACE_LOOKUP))
 328                                goto permission_denied;
 329                } else if (mask & MAY_READ) {
 330                        if (!(access & AFS_ACE_READ))
 331                                goto permission_denied;
 332                } else if (mask & MAY_WRITE) {
 333                        if (!(access & (AFS_ACE_DELETE | /* rmdir, unlink, rename from */
 334                                        AFS_ACE_INSERT | /* create, mkdir, symlink, rename to */
 335                                        AFS_ACE_WRITE))) /* chmod */
 336                                goto permission_denied;
 337                } else {
 338                        BUG();
 339                }
 340        } else {
 341                if (!(access & AFS_ACE_LOOKUP))
 342                        goto permission_denied;
 343                if (mask & (MAY_EXEC | MAY_READ)) {
 344                        if (!(access & AFS_ACE_READ))
 345                                goto permission_denied;
 346                } else if (mask & MAY_WRITE) {
 347                        if (!(access & AFS_ACE_WRITE))
 348                                goto permission_denied;
 349                }
 350        }
 351
 352        key_put(key);
 353        ret = generic_permission(inode, mask);
 354        _leave(" = %d", ret);
 355        return ret;
 356
 357permission_denied:
 358        ret = -EACCES;
 359error:
 360        key_put(key);
 361        _leave(" = %d", ret);
 362        return ret;
 363}
 364
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