![David Howells](/assets/img/avatar_default.png)
Fix the AFS file locking whereby the use of the big kernel lock (which
could be slept with) was replaced by a spinlock (which couldn't). The
problem is that the AFS code was doing stuff inside the critical section
that might call schedule(), so this is a broken transformation.
Fix this by the following means:
(1) Use a state machine with a proper state that can only be changed under
the spinlock rather than using a collection of bit flags.
(2) Cache the key used for the lock and the lock type in the afs_vnode
struct so that the manager work function doesn't have to refer to a
file_lock struct that's been dequeued. This makes signal handling
safer.
(4) Move the unlock from afs_do_unlk() to afs_fl_release_private() which
means that unlock is achieved in other circumstances too.
(5) Unlock the file on the server before taking the next conflicting lock.
Also change:
(1) Check the permits on a file before actually trying the lock.
(2) fsync the file before effecting an explicit unlock operation. We
don't fsync if the lock is erased otherwise as we might not be in a
context where we can actually do that.
Further fixes:
(1) Fixed-fileserver address rotation is made to work. It's only used by
the locking functions, so couldn't be tested before.
Fixes: 72f98e7255
("locks: turn lock_flocks into a spinlock")
Signed-off-by: David Howells <dhowells@redhat.com>
cc: jlayton@redhat.com
430 lines
10 KiB
C
430 lines
10 KiB
C
/* AFS security handling
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*
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* Copyright (C) 2007, 2017 Red Hat, Inc. All Rights Reserved.
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* Written by David Howells (dhowells@redhat.com)
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*
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* This program is free software; you can redistribute it and/or
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* modify it under the terms of the GNU General Public License
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* as published by the Free Software Foundation; either version
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* 2 of the License, or (at your option) any later version.
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*/
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#include <linux/init.h>
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#include <linux/slab.h>
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#include <linux/fs.h>
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#include <linux/ctype.h>
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#include <linux/sched.h>
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#include <linux/hashtable.h>
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#include <keys/rxrpc-type.h>
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#include "internal.h"
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static DEFINE_HASHTABLE(afs_permits_cache, 10);
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static DEFINE_SPINLOCK(afs_permits_lock);
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/*
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* get a key
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*/
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struct key *afs_request_key(struct afs_cell *cell)
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{
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struct key *key;
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_enter("{%x}", key_serial(cell->anonymous_key));
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_debug("key %s", cell->anonymous_key->description);
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key = request_key(&key_type_rxrpc, cell->anonymous_key->description,
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NULL);
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if (IS_ERR(key)) {
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if (PTR_ERR(key) != -ENOKEY) {
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_leave(" = %ld", PTR_ERR(key));
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return key;
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}
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/* act as anonymous user */
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_leave(" = {%x} [anon]", key_serial(cell->anonymous_key));
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return key_get(cell->anonymous_key);
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} else {
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/* act as authorised user */
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_leave(" = {%x} [auth]", key_serial(key));
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return key;
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}
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}
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/*
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* Dispose of a list of permits.
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*/
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static void afs_permits_rcu(struct rcu_head *rcu)
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{
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struct afs_permits *permits =
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container_of(rcu, struct afs_permits, rcu);
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int i;
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for (i = 0; i < permits->nr_permits; i++)
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key_put(permits->permits[i].key);
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kfree(permits);
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}
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/*
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* Discard a permission cache.
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*/
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void afs_put_permits(struct afs_permits *permits)
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{
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if (permits && refcount_dec_and_test(&permits->usage)) {
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spin_lock(&afs_permits_lock);
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hash_del_rcu(&permits->hash_node);
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spin_unlock(&afs_permits_lock);
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call_rcu(&permits->rcu, afs_permits_rcu);
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}
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}
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/*
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* Clear a permit cache on callback break.
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*/
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void afs_clear_permits(struct afs_vnode *vnode)
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{
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struct afs_permits *permits;
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spin_lock(&vnode->lock);
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permits = rcu_dereference_protected(vnode->permit_cache,
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lockdep_is_held(&vnode->lock));
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RCU_INIT_POINTER(vnode->permit_cache, NULL);
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vnode->cb_break++;
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spin_unlock(&vnode->lock);
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if (permits)
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afs_put_permits(permits);
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}
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/*
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* Hash a list of permits. Use simple addition to make it easy to add an extra
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* one at an as-yet indeterminate position in the list.
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*/
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static void afs_hash_permits(struct afs_permits *permits)
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{
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unsigned long h = permits->nr_permits;
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int i;
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for (i = 0; i < permits->nr_permits; i++) {
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h += (unsigned long)permits->permits[i].key / sizeof(void *);
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h += permits->permits[i].access;
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}
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permits->h = h;
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}
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/*
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* Cache the CallerAccess result obtained from doing a fileserver operation
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* that returned a vnode status for a particular key. If a callback break
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* occurs whilst the operation was in progress then we have to ditch the cache
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* as the ACL *may* have changed.
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*/
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void afs_cache_permit(struct afs_vnode *vnode, struct key *key,
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unsigned int cb_break)
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{
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struct afs_permits *permits, *xpermits, *replacement, *new = NULL;
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afs_access_t caller_access = READ_ONCE(vnode->status.caller_access);
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size_t size = 0;
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bool changed = false;
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int i, j;
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_enter("{%x:%u},%x,%x",
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vnode->fid.vid, vnode->fid.vnode, key_serial(key), caller_access);
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rcu_read_lock();
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/* Check for the common case first: We got back the same access as last
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* time we tried and already have it recorded.
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*/
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permits = rcu_dereference(vnode->permit_cache);
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if (permits) {
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if (!permits->invalidated) {
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for (i = 0; i < permits->nr_permits; i++) {
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if (permits->permits[i].key < key)
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continue;
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if (permits->permits[i].key > key)
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break;
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if (permits->permits[i].access != caller_access) {
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changed = true;
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break;
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}
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if (cb_break != (vnode->cb_break +
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vnode->cb_interest->server->cb_s_break)) {
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changed = true;
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break;
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}
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/* The cache is still good. */
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rcu_read_unlock();
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return;
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}
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}
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changed |= permits->invalidated;
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size = permits->nr_permits;
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/* If this set of permits is now wrong, clear the permits
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* pointer so that no one tries to use the stale information.
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*/
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if (changed) {
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spin_lock(&vnode->lock);
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if (permits != rcu_access_pointer(vnode->permit_cache))
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goto someone_else_changed_it_unlock;
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RCU_INIT_POINTER(vnode->permit_cache, NULL);
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spin_unlock(&vnode->lock);
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afs_put_permits(permits);
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permits = NULL;
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size = 0;
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}
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}
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if (cb_break != (vnode->cb_break + vnode->cb_interest->server->cb_s_break)) {
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rcu_read_unlock();
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goto someone_else_changed_it;
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}
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/* We need a ref on any permits list we want to copy as we'll have to
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* drop the lock to do memory allocation.
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*/
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if (permits && !refcount_inc_not_zero(&permits->usage)) {
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rcu_read_unlock();
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goto someone_else_changed_it;
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}
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rcu_read_unlock();
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/* Speculatively create a new list with the revised permission set. We
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* discard this if we find an extant match already in the hash, but
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* it's easier to compare with memcmp this way.
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*
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* We fill in the key pointers at this time, but we don't get the refs
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* yet.
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*/
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size++;
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new = kzalloc(sizeof(struct afs_permits) +
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sizeof(struct afs_permit) * size, GFP_NOFS);
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if (!new)
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return;
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refcount_set(&new->usage, 1);
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new->nr_permits = size;
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i = j = 0;
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if (permits) {
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for (i = 0; i < permits->nr_permits; i++) {
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if (j == i && permits->permits[i].key > key) {
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new->permits[j].key = key;
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new->permits[j].access = caller_access;
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j++;
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}
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new->permits[j].key = permits->permits[i].key;
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new->permits[j].access = permits->permits[i].access;
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j++;
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}
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}
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if (j == i) {
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new->permits[j].key = key;
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new->permits[j].access = caller_access;
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}
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afs_hash_permits(new);
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afs_put_permits(permits);
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/* Now see if the permit list we want is actually already available */
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spin_lock(&afs_permits_lock);
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hash_for_each_possible(afs_permits_cache, xpermits, hash_node, new->h) {
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if (xpermits->h != new->h ||
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xpermits->invalidated ||
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xpermits->nr_permits != new->nr_permits ||
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memcmp(xpermits->permits, new->permits,
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new->nr_permits * sizeof(struct afs_permit)) != 0)
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continue;
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if (refcount_inc_not_zero(&xpermits->usage)) {
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replacement = xpermits;
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goto found;
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}
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break;
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}
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for (i = 0; i < new->nr_permits; i++)
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key_get(new->permits[i].key);
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hash_add_rcu(afs_permits_cache, &new->hash_node, new->h);
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replacement = new;
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new = NULL;
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found:
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spin_unlock(&afs_permits_lock);
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kfree(new);
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spin_lock(&vnode->lock);
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if (cb_break != (vnode->cb_break + vnode->cb_interest->server->cb_s_break) ||
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permits != rcu_access_pointer(vnode->permit_cache))
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goto someone_else_changed_it_unlock;
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rcu_assign_pointer(vnode->permit_cache, replacement);
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spin_unlock(&vnode->lock);
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afs_put_permits(permits);
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return;
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someone_else_changed_it_unlock:
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spin_unlock(&vnode->lock);
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someone_else_changed_it:
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/* Someone else changed the cache under us - don't recheck at this
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* time.
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*/
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return;
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}
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/*
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* check with the fileserver to see if the directory or parent directory is
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* permitted to be accessed with this authorisation, and if so, what access it
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* is granted
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*/
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int afs_check_permit(struct afs_vnode *vnode, struct key *key,
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afs_access_t *_access)
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{
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struct afs_permits *permits;
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bool valid = false;
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int i, ret;
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_enter("{%x:%u},%x",
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vnode->fid.vid, vnode->fid.vnode, key_serial(key));
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permits = vnode->permit_cache;
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/* check the permits to see if we've got one yet */
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if (key == vnode->volume->cell->anonymous_key) {
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_debug("anon");
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*_access = vnode->status.anon_access;
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valid = true;
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} else {
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rcu_read_lock();
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permits = rcu_dereference(vnode->permit_cache);
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if (permits) {
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for (i = 0; i < permits->nr_permits; i++) {
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if (permits->permits[i].key < key)
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continue;
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if (permits->permits[i].key > key)
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break;
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*_access = permits->permits[i].access;
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valid = !permits->invalidated;
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break;
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}
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}
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rcu_read_unlock();
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}
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if (!valid) {
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/* Check the status on the file we're actually interested in
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* (the post-processing will cache the result).
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*/
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_debug("no valid permit");
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ret = afs_fetch_status(vnode, key);
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if (ret < 0) {
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*_access = 0;
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_leave(" = %d", ret);
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return ret;
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}
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*_access = vnode->status.caller_access;
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}
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_leave(" = 0 [access %x]", *_access);
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return 0;
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}
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/*
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* check the permissions on an AFS file
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* - AFS ACLs are attached to directories only, and a file is controlled by its
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* parent directory's ACL
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*/
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int afs_permission(struct inode *inode, int mask)
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{
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struct afs_vnode *vnode = AFS_FS_I(inode);
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afs_access_t uninitialized_var(access);
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struct key *key;
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int ret;
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if (mask & MAY_NOT_BLOCK)
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return -ECHILD;
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_enter("{{%x:%u},%lx},%x,",
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vnode->fid.vid, vnode->fid.vnode, vnode->flags, mask);
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key = afs_request_key(vnode->volume->cell);
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if (IS_ERR(key)) {
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_leave(" = %ld [key]", PTR_ERR(key));
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return PTR_ERR(key);
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}
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ret = afs_validate(vnode, key);
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if (ret < 0)
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goto error;
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/* check the permits to see if we've got one yet */
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ret = afs_check_permit(vnode, key, &access);
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if (ret < 0)
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goto error;
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/* interpret the access mask */
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_debug("REQ %x ACC %x on %s",
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mask, access, S_ISDIR(inode->i_mode) ? "dir" : "file");
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if (S_ISDIR(inode->i_mode)) {
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if (mask & MAY_EXEC) {
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if (!(access & AFS_ACE_LOOKUP))
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goto permission_denied;
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} else if (mask & MAY_READ) {
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if (!(access & AFS_ACE_LOOKUP))
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goto permission_denied;
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} else if (mask & MAY_WRITE) {
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if (!(access & (AFS_ACE_DELETE | /* rmdir, unlink, rename from */
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AFS_ACE_INSERT))) /* create, mkdir, symlink, rename to */
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goto permission_denied;
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} else {
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BUG();
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}
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} else {
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if (!(access & AFS_ACE_LOOKUP))
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goto permission_denied;
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if ((mask & MAY_EXEC) && !(inode->i_mode & S_IXUSR))
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goto permission_denied;
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if (mask & (MAY_EXEC | MAY_READ)) {
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if (!(access & AFS_ACE_READ))
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goto permission_denied;
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if (!(inode->i_mode & S_IRUSR))
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goto permission_denied;
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} else if (mask & MAY_WRITE) {
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if (!(access & AFS_ACE_WRITE))
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goto permission_denied;
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if (!(inode->i_mode & S_IWUSR))
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goto permission_denied;
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}
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}
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key_put(key);
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_leave(" = %d", ret);
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return ret;
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permission_denied:
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ret = -EACCES;
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error:
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key_put(key);
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_leave(" = %d", ret);
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return ret;
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}
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void __exit afs_clean_up_permit_cache(void)
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{
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int i;
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for (i = 0; i < HASH_SIZE(afs_permits_cache); i++)
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WARN_ON_ONCE(!hlist_empty(&afs_permits_cache[i]));
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}
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