From: Baokun Li libaokun1@huawei.com
[ Upstream commit 5d8f805789072ea7fd39504694b7bd17e5f751c4 ]
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: fe2140e2f57f ("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 Signed-off-by: Baokun Li libaokun1@huawei.com --- fs/cachefiles/cache.c | 35 ++++++++++++++++++++++++++++++++++- fs/cachefiles/volume.c | 1 - 2 files changed, 34 insertions(+), 2 deletions(-)
diff --git a/fs/cachefiles/cache.c b/fs/cachefiles/cache.c index 56ef519a36a0..9fb06dc16520 100644 --- a/fs/cachefiles/cache.c +++ b/fs/cachefiles/cache.c @@ -313,7 +313,39 @@ static void cachefiles_withdraw_objects(struct cachefiles_cache *cache) }
/* - * Withdraw volumes. + * Withdraw fscache volumes. + */ +static void cachefiles_withdraw_fscache_volumes(struct cachefiles_cache *cache) +{ + struct list_head *cur; + struct cachefiles_volume *volume; + struct fscache_volume *vcookie; + + _enter(""); +retry: + spin_lock(&cache->object_list_lock); + list_for_each(cur, &cache->volumes) { + volume = list_entry(cur, struct cachefiles_volume, cache_link); + + if (atomic_read(&volume->vcookie->n_accesses) == 0) + continue; + + vcookie = fscache_try_get_volume(volume->vcookie, + fscache_volume_get_withdraw); + if (vcookie) { + spin_unlock(&cache->object_list_lock); + fscache_withdraw_volume(vcookie); + fscache_put_volume(vcookie, fscache_volume_put_withdraw); + goto retry; + } + } + spin_unlock(&cache->object_list_lock); + + _leave(""); +} + +/* + * Withdraw cachefiles volumes. */ static void cachefiles_withdraw_volumes(struct cachefiles_cache *cache) { @@ -381,6 +413,7 @@ void cachefiles_withdraw_cache(struct cachefiles_cache *cache) pr_info("File cache on %s unregistering\n", fscache->name);
fscache_withdraw_cache(fscache); + cachefiles_withdraw_fscache_volumes(cache);
/* we now have to destroy all the active objects pertaining to this * cache - which we do by passing them off to thread pool to be diff --git a/fs/cachefiles/volume.c b/fs/cachefiles/volume.c index 89df0ba8ba5e..781aac4ef274 100644 --- a/fs/cachefiles/volume.c +++ b/fs/cachefiles/volume.c @@ -133,7 +133,6 @@ void cachefiles_free_volume(struct fscache_volume *vcookie)
void cachefiles_withdraw_volume(struct cachefiles_volume *volume) { - fscache_withdraw_volume(volume->vcookie); cachefiles_set_volume_xattr(volume); __cachefiles_free_volume(volume); }