linux/fs/afs/security.c
David Howells 1bcab12521 afs: Fix permit refcounting
Fix four refcount bugs in afs_cache_permit():

 (1) When checking the result of the kzalloc(), we can't just return, but
     must put 'permits'.

 (2) We shouldn't put permits immediately after hashing a new permit as we
     need to keep the pointer stable so that we can check to see if
     vnode->permit_cache has changed before we decide whether to assign to
     it.

 (3) 'permits' is being put twice.

 (4) We need to put either the replacement or the thing replaced after the
     assignment to vnode->permit_cache.

Without this, lots of the following are seen:

  Kernel BUG at ffffffffa039857b [verbose debug info unavailable]
  ------------[ cut here ]------------
  Kernel BUG at ffffffffa039858a [verbose debug info unavailable]
  ------------[ cut here ]------------

The addresses are in the .text..refcount section of the kafs.ko module.
Following the relocation records for the __ex_table section shows one to be
due to the decrement in afs_put_permits() and the other to be key_get() in
afs_cache_permit().

Occasionally, the following is seen:

  refcount_t overflow at afs_cache_permit+0x57d/0x5c0 [kafs] in cc1[562], uid/euid: 0/0
  WARNING: CPU: 0 PID: 562 at kernel/panic.c:657 refcount_error_report+0x9c/0xac
  ...

Reported-by: Marc Dionne <marc.dionne@auristor.com>
Signed-off-by: David Howells <dhowells@redhat.com>
Tested-by: Marc Dionne <marc.dionne@auristor.com>
2017-12-01 11:40:43 +00:00

432 lines
10 KiB
C

/* AFS security handling
*
* Copyright (C) 2007, 2017 Red Hat, Inc. All Rights Reserved.
* Written by David Howells (dhowells@redhat.com)
*
* This program is free software; you can redistribute it and/or
* modify it under the terms of the GNU General Public License
* as published by the Free Software Foundation; either version
* 2 of the License, or (at your option) any later version.
*/
#include <linux/init.h>
#include <linux/slab.h>
#include <linux/fs.h>
#include <linux/ctype.h>
#include <linux/sched.h>
#include <linux/hashtable.h>
#include <keys/rxrpc-type.h>
#include "internal.h"
static DEFINE_HASHTABLE(afs_permits_cache, 10);
static DEFINE_SPINLOCK(afs_permits_lock);
/*
* get a key
*/
struct key *afs_request_key(struct afs_cell *cell)
{
struct key *key;
_enter("{%x}", key_serial(cell->anonymous_key));
_debug("key %s", cell->anonymous_key->description);
key = request_key(&key_type_rxrpc, cell->anonymous_key->description,
NULL);
if (IS_ERR(key)) {
if (PTR_ERR(key) != -ENOKEY) {
_leave(" = %ld", PTR_ERR(key));
return key;
}
/* act as anonymous user */
_leave(" = {%x} [anon]", key_serial(cell->anonymous_key));
return key_get(cell->anonymous_key);
} else {
/* act as authorised user */
_leave(" = {%x} [auth]", key_serial(key));
return key;
}
}
/*
* Dispose of a list of permits.
*/
static void afs_permits_rcu(struct rcu_head *rcu)
{
struct afs_permits *permits =
container_of(rcu, struct afs_permits, rcu);
int i;
for (i = 0; i < permits->nr_permits; i++)
key_put(permits->permits[i].key);
kfree(permits);
}
/*
* Discard a permission cache.
*/
void afs_put_permits(struct afs_permits *permits)
{
if (permits && refcount_dec_and_test(&permits->usage)) {
spin_lock(&afs_permits_lock);
hash_del_rcu(&permits->hash_node);
spin_unlock(&afs_permits_lock);
call_rcu(&permits->rcu, afs_permits_rcu);
}
}
/*
* Clear a permit cache on callback break.
*/
void afs_clear_permits(struct afs_vnode *vnode)
{
struct afs_permits *permits;
spin_lock(&vnode->lock);
permits = rcu_dereference_protected(vnode->permit_cache,
lockdep_is_held(&vnode->lock));
RCU_INIT_POINTER(vnode->permit_cache, NULL);
vnode->cb_break++;
spin_unlock(&vnode->lock);
if (permits)
afs_put_permits(permits);
}
/*
* Hash a list of permits. Use simple addition to make it easy to add an extra
* one at an as-yet indeterminate position in the list.
*/
static void afs_hash_permits(struct afs_permits *permits)
{
unsigned long h = permits->nr_permits;
int i;
for (i = 0; i < permits->nr_permits; i++) {
h += (unsigned long)permits->permits[i].key / sizeof(void *);
h += permits->permits[i].access;
}
permits->h = h;
}
/*
* Cache the CallerAccess result obtained from doing a fileserver operation
* that returned a vnode status for a particular key. If a callback break
* occurs whilst the operation was in progress then we have to ditch the cache
* as the ACL *may* have changed.
*/
void afs_cache_permit(struct afs_vnode *vnode, struct key *key,
unsigned int cb_break)
{
struct afs_permits *permits, *xpermits, *replacement, *zap, *new = NULL;
afs_access_t caller_access = READ_ONCE(vnode->status.caller_access);
size_t size = 0;
bool changed = false;
int i, j;
_enter("{%x:%u},%x,%x",
vnode->fid.vid, vnode->fid.vnode, key_serial(key), caller_access);
rcu_read_lock();
/* Check for the common case first: We got back the same access as last
* time we tried and already have it recorded.
*/
permits = rcu_dereference(vnode->permit_cache);
if (permits) {
if (!permits->invalidated) {
for (i = 0; i < permits->nr_permits; i++) {
if (permits->permits[i].key < key)
continue;
if (permits->permits[i].key > key)
break;
if (permits->permits[i].access != caller_access) {
changed = true;
break;
}
if (cb_break != (vnode->cb_break +
vnode->cb_interest->server->cb_s_break)) {
changed = true;
break;
}
/* The cache is still good. */
rcu_read_unlock();
return;
}
}
changed |= permits->invalidated;
size = permits->nr_permits;
/* If this set of permits is now wrong, clear the permits
* pointer so that no one tries to use the stale information.
*/
if (changed) {
spin_lock(&vnode->lock);
if (permits != rcu_access_pointer(vnode->permit_cache))
goto someone_else_changed_it_unlock;
RCU_INIT_POINTER(vnode->permit_cache, NULL);
spin_unlock(&vnode->lock);
afs_put_permits(permits);
permits = NULL;
size = 0;
}
}
if (cb_break != (vnode->cb_break + vnode->cb_interest->server->cb_s_break)) {
rcu_read_unlock();
goto someone_else_changed_it;
}
/* We need a ref on any permits list we want to copy as we'll have to
* drop the lock to do memory allocation.
*/
if (permits && !refcount_inc_not_zero(&permits->usage)) {
rcu_read_unlock();
goto someone_else_changed_it;
}
rcu_read_unlock();
/* Speculatively create a new list with the revised permission set. We
* discard this if we find an extant match already in the hash, but
* it's easier to compare with memcmp this way.
*
* We fill in the key pointers at this time, but we don't get the refs
* yet.
*/
size++;
new = kzalloc(sizeof(struct afs_permits) +
sizeof(struct afs_permit) * size, GFP_NOFS);
if (!new)
goto out_put;
refcount_set(&new->usage, 1);
new->nr_permits = size;
i = j = 0;
if (permits) {
for (i = 0; i < permits->nr_permits; i++) {
if (j == i && permits->permits[i].key > key) {
new->permits[j].key = key;
new->permits[j].access = caller_access;
j++;
}
new->permits[j].key = permits->permits[i].key;
new->permits[j].access = permits->permits[i].access;
j++;
}
}
if (j == i) {
new->permits[j].key = key;
new->permits[j].access = caller_access;
}
afs_hash_permits(new);
/* Now see if the permit list we want is actually already available */
spin_lock(&afs_permits_lock);
hash_for_each_possible(afs_permits_cache, xpermits, hash_node, new->h) {
if (xpermits->h != new->h ||
xpermits->invalidated ||
xpermits->nr_permits != new->nr_permits ||
memcmp(xpermits->permits, new->permits,
new->nr_permits * sizeof(struct afs_permit)) != 0)
continue;
if (refcount_inc_not_zero(&xpermits->usage)) {
replacement = xpermits;
goto found;
}
break;
}
for (i = 0; i < new->nr_permits; i++)
key_get(new->permits[i].key);
hash_add_rcu(afs_permits_cache, &new->hash_node, new->h);
replacement = new;
new = NULL;
found:
spin_unlock(&afs_permits_lock);
kfree(new);
spin_lock(&vnode->lock);
zap = rcu_access_pointer(vnode->permit_cache);
if (cb_break == (vnode->cb_break + vnode->cb_interest->server->cb_s_break) &&
zap == permits)
rcu_assign_pointer(vnode->permit_cache, replacement);
else
zap = replacement;
spin_unlock(&vnode->lock);
afs_put_permits(zap);
out_put:
afs_put_permits(permits);
return;
someone_else_changed_it_unlock:
spin_unlock(&vnode->lock);
someone_else_changed_it:
/* Someone else changed the cache under us - don't recheck at this
* time.
*/
return;
}
/*
* check with the fileserver to see if the directory or parent directory is
* permitted to be accessed with this authorisation, and if so, what access it
* is granted
*/
int afs_check_permit(struct afs_vnode *vnode, struct key *key,
afs_access_t *_access)
{
struct afs_permits *permits;
bool valid = false;
int i, ret;
_enter("{%x:%u},%x",
vnode->fid.vid, vnode->fid.vnode, key_serial(key));
permits = vnode->permit_cache;
/* check the permits to see if we've got one yet */
if (key == vnode->volume->cell->anonymous_key) {
_debug("anon");
*_access = vnode->status.anon_access;
valid = true;
} else {
rcu_read_lock();
permits = rcu_dereference(vnode->permit_cache);
if (permits) {
for (i = 0; i < permits->nr_permits; i++) {
if (permits->permits[i].key < key)
continue;
if (permits->permits[i].key > key)
break;
*_access = permits->permits[i].access;
valid = !permits->invalidated;
break;
}
}
rcu_read_unlock();
}
if (!valid) {
/* Check the status on the file we're actually interested in
* (the post-processing will cache the result).
*/
_debug("no valid permit");
ret = afs_fetch_status(vnode, key);
if (ret < 0) {
*_access = 0;
_leave(" = %d", ret);
return ret;
}
*_access = vnode->status.caller_access;
}
_leave(" = 0 [access %x]", *_access);
return 0;
}
/*
* check the permissions on an AFS file
* - AFS ACLs are attached to directories only, and a file is controlled by its
* parent directory's ACL
*/
int afs_permission(struct inode *inode, int mask)
{
struct afs_vnode *vnode = AFS_FS_I(inode);
afs_access_t uninitialized_var(access);
struct key *key;
int ret;
if (mask & MAY_NOT_BLOCK)
return -ECHILD;
_enter("{{%x:%u},%lx},%x,",
vnode->fid.vid, vnode->fid.vnode, vnode->flags, mask);
key = afs_request_key(vnode->volume->cell);
if (IS_ERR(key)) {
_leave(" = %ld [key]", PTR_ERR(key));
return PTR_ERR(key);
}
ret = afs_validate(vnode, key);
if (ret < 0)
goto error;
/* check the permits to see if we've got one yet */
ret = afs_check_permit(vnode, key, &access);
if (ret < 0)
goto error;
/* interpret the access mask */
_debug("REQ %x ACC %x on %s",
mask, access, S_ISDIR(inode->i_mode) ? "dir" : "file");
if (S_ISDIR(inode->i_mode)) {
if (mask & MAY_EXEC) {
if (!(access & AFS_ACE_LOOKUP))
goto permission_denied;
} else if (mask & MAY_READ) {
if (!(access & AFS_ACE_LOOKUP))
goto permission_denied;
} else if (mask & MAY_WRITE) {
if (!(access & (AFS_ACE_DELETE | /* rmdir, unlink, rename from */
AFS_ACE_INSERT))) /* create, mkdir, symlink, rename to */
goto permission_denied;
} else {
BUG();
}
} else {
if (!(access & AFS_ACE_LOOKUP))
goto permission_denied;
if ((mask & MAY_EXEC) && !(inode->i_mode & S_IXUSR))
goto permission_denied;
if (mask & (MAY_EXEC | MAY_READ)) {
if (!(access & AFS_ACE_READ))
goto permission_denied;
if (!(inode->i_mode & S_IRUSR))
goto permission_denied;
} else if (mask & MAY_WRITE) {
if (!(access & AFS_ACE_WRITE))
goto permission_denied;
if (!(inode->i_mode & S_IWUSR))
goto permission_denied;
}
}
key_put(key);
_leave(" = %d", ret);
return ret;
permission_denied:
ret = -EACCES;
error:
key_put(key);
_leave(" = %d", ret);
return ret;
}
void __exit afs_clean_up_permit_cache(void)
{
int i;
for (i = 0; i < HASH_SIZE(afs_permits_cache); i++)
WARN_ON_ONCE(!hlist_empty(&afs_permits_cache[i]));
}