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5d8f805789
We got the following issue in our fault injection stress test:
==================================================================
BUG: KASAN: slab-use-after-free in cachefiles_withdraw_cookie+0x4d9/0x600
Read of size 8 at addr ffff888118efc000 by task kworker/u78:0/109
CPU: 13 PID: 109 Comm: kworker/u78:0 Not tainted 6.8.0-dirty #566
Call Trace:
<TASK>
kasan_report+0x93/0xc0
cachefiles_withdraw_cookie+0x4d9/0x600
fscache_cookie_state_machine+0x5c8/0x1230
fscache_cookie_worker+0x91/0x1c0
process_one_work+0x7fa/0x1800
[...]
Allocated by task 117:
kmalloc_trace+0x1b3/0x3c0
cachefiles_acquire_volume+0xf3/0x9c0
fscache_create_volume_work+0x97/0x150
process_one_work+0x7fa/0x1800
[...]
Freed by task 120301:
kfree+0xf1/0x2c0
cachefiles_withdraw_cache+0x3fa/0x920
cachefiles_put_unbind_pincount+0x1f6/0x250
cachefiles_daemon_release+0x13b/0x290
__fput+0x204/0xa00
task_work_run+0x139/0x230
do_exit+0x87a/0x29b0
[...]
==================================================================
Following is the process that triggers the issue:
p1 | p2
------------------------------------------------------------
fscache_begin_lookup
fscache_begin_volume_access
fscache_cache_is_live(fscache_cache)
cachefiles_daemon_release
cachefiles_put_unbind_pincount
cachefiles_daemon_unbind
cachefiles_withdraw_cache
fscache_withdraw_cache
fscache_set_cache_state(cache, FSCACHE_CACHE_IS_WITHDRAWN);
cachefiles_withdraw_objects(cache)
fscache_wait_for_objects(fscache)
atomic_read(&fscache_cache->object_count) == 0
fscache_perform_lookup
cachefiles_lookup_cookie
cachefiles_alloc_object
refcount_set(&object->ref, 1);
object->volume = volume
fscache_count_object(vcookie->cache);
atomic_inc(&fscache_cache->object_count)
cachefiles_withdraw_volumes
cachefiles_withdraw_volume
fscache_withdraw_volume
__cachefiles_free_volume
kfree(cachefiles_volume)
fscache_cookie_state_machine
cachefiles_withdraw_cookie
cache = object->volume->cache;
// cachefiles_volume UAF !!!
After setting FSCACHE_CACHE_IS_WITHDRAWN, wait for all the cookie lookups
to complete first, and then wait for fscache_cache->object_count == 0 to
avoid the cookie exiting after the volume has been freed and triggering
the above issue. Therefore call fscache_withdraw_volume() before calling
cachefiles_withdraw_objects().
This way, after setting FSCACHE_CACHE_IS_WITHDRAWN, only the following two
cases will occur:
1) fscache_begin_lookup fails in fscache_begin_volume_access().
2) fscache_withdraw_volume() will ensure that fscache_count_object() has
been executed before calling fscache_wait_for_objects().
Fixes: fe2140e2f5 ("cachefiles: Implement volume support")
Suggested-by: Hou Tao <houtao1@huawei.com>
Signed-off-by: Baokun Li <libaokun1@huawei.com>
Link: https://lore.kernel.org/r/20240628062930.2467993-4-libaokun@huaweicloud.com
Signed-off-by: Christian Brauner <brauner@kernel.org>
138 lines
3.3 KiB
C
138 lines
3.3 KiB
C
// SPDX-License-Identifier: GPL-2.0-or-later
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/* Volume handling.
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*
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* Copyright (C) 2021 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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#include <linux/fs.h>
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#include <linux/slab.h>
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#include "internal.h"
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#include <trace/events/fscache.h>
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/*
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* Allocate and set up a volume representation. We make sure all the fanout
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* directories are created and pinned.
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*/
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void cachefiles_acquire_volume(struct fscache_volume *vcookie)
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{
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struct cachefiles_volume *volume;
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struct cachefiles_cache *cache = vcookie->cache->cache_priv;
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const struct cred *saved_cred;
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struct dentry *vdentry, *fan;
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size_t len;
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char *name;
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bool is_new = false;
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int ret, n_accesses, i;
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_enter("");
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volume = kzalloc(sizeof(struct cachefiles_volume), GFP_KERNEL);
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if (!volume)
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return;
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volume->vcookie = vcookie;
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volume->cache = cache;
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INIT_LIST_HEAD(&volume->cache_link);
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cachefiles_begin_secure(cache, &saved_cred);
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len = vcookie->key[0];
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name = kmalloc(len + 3, GFP_NOFS);
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if (!name)
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goto error_vol;
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name[0] = 'I';
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memcpy(name + 1, vcookie->key + 1, len);
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name[len + 1] = 0;
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retry:
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vdentry = cachefiles_get_directory(cache, cache->store, name, &is_new);
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if (IS_ERR(vdentry))
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goto error_name;
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volume->dentry = vdentry;
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if (is_new) {
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if (!cachefiles_set_volume_xattr(volume))
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goto error_dir;
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} else {
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ret = cachefiles_check_volume_xattr(volume);
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if (ret < 0) {
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if (ret != -ESTALE)
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goto error_dir;
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inode_lock_nested(d_inode(cache->store), I_MUTEX_PARENT);
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cachefiles_bury_object(cache, NULL, cache->store, vdentry,
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FSCACHE_VOLUME_IS_WEIRD);
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cachefiles_put_directory(volume->dentry);
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cond_resched();
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goto retry;
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}
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}
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for (i = 0; i < 256; i++) {
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sprintf(name, "@%02x", i);
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fan = cachefiles_get_directory(cache, vdentry, name, NULL);
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if (IS_ERR(fan))
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goto error_fan;
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volume->fanout[i] = fan;
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}
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cachefiles_end_secure(cache, saved_cred);
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vcookie->cache_priv = volume;
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n_accesses = atomic_inc_return(&vcookie->n_accesses); /* Stop wakeups on dec-to-0 */
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trace_fscache_access_volume(vcookie->debug_id, 0,
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refcount_read(&vcookie->ref),
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n_accesses, fscache_access_cache_pin);
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spin_lock(&cache->object_list_lock);
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list_add(&volume->cache_link, &volume->cache->volumes);
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spin_unlock(&cache->object_list_lock);
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kfree(name);
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return;
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error_fan:
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for (i = 0; i < 256; i++)
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cachefiles_put_directory(volume->fanout[i]);
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error_dir:
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cachefiles_put_directory(volume->dentry);
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error_name:
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kfree(name);
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error_vol:
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kfree(volume);
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cachefiles_end_secure(cache, saved_cred);
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}
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/*
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* Release a volume representation.
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*/
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static void __cachefiles_free_volume(struct cachefiles_volume *volume)
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{
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int i;
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_enter("");
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volume->vcookie->cache_priv = NULL;
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for (i = 0; i < 256; i++)
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cachefiles_put_directory(volume->fanout[i]);
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cachefiles_put_directory(volume->dentry);
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kfree(volume);
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}
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void cachefiles_free_volume(struct fscache_volume *vcookie)
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{
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struct cachefiles_volume *volume = vcookie->cache_priv;
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if (volume) {
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spin_lock(&volume->cache->object_list_lock);
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list_del_init(&volume->cache_link);
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spin_unlock(&volume->cache->object_list_lock);
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__cachefiles_free_volume(volume);
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}
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}
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void cachefiles_withdraw_volume(struct cachefiles_volume *volume)
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{
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cachefiles_set_volume_xattr(volume);
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__cachefiles_free_volume(volume);
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}
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