Re: [PATCH v2 04/12] cachefiles: fix slab-use-after-free in cachefiles_ondemand_daemon_read()

Baokun Li
2024-05-20T08:56:54Z

On 2024/5/20 15:36, Jingbo Xu wrote:
>
> On 5/15/24 4:45 PM, libaokun@huaweicloud.com wrote:
>> From: Baokun Li <libaokun1@huawei.com>
>>
>> We got the following issue in a fuzz test of randomly issuing the restore
>> command:
>>
>> ==================================================================
>> BUG: KASAN: slab-use-after-free in cachefiles_ondemand_daemon_read+0xb41/0xb60
>> Read of size 8 at addr ffff888122e84088 by task ondemand-04-dae/963
>>
>> CPU: 13 PID: 963 Comm: ondemand-04-dae Not tainted 6.8.0-dirty #564
>> Call Trace:
>> kasan_report+0x93/0xc0
>> cachefiles_ondemand_daemon_read+0xb41/0xb60
>> vfs_read+0x169/0xb50
>> ksys_read+0xf5/0x1e0
>>
>> Allocated by task 116:
>> kmem_cache_alloc+0x140/0x3a0
>> cachefiles_lookup_cookie+0x140/0xcd0
>> fscache_cookie_state_machine+0x43c/0x1230
>> [...]
>>
>> Freed by task 792:
>> kmem_cache_free+0xfe/0x390
>> cachefiles_put_object+0x241/0x480
>> fscache_cookie_state_machine+0x5c8/0x1230
>> [...]
>> ==================================================================
>>
>> Following is the process that triggers the issue:
>>
>> mount | daemon_thread1 | daemon_thread2
>> ------------------------------------------------------------
>> cachefiles_withdraw_cookie
>> cachefiles_ondemand_clean_object(object)
>> cachefiles_ondemand_send_req
>> REQ_A = kzalloc(sizeof(*req) + data_len)
>> wait_for_completion(&REQ_A->done)
>>
>> cachefiles_daemon_read
>> cachefiles_ondemand_daemon_read
>> REQ_A = cachefiles_ondemand_select_req
>> msg->object_id = req->object->ondemand->ondemand_id
>> ------ restore ------
>> cachefiles_ondemand_restore
>> xas_for_each(&xas, req, ULONG_MAX)
>> xas_set_mark(&xas, CACHEFILES_REQ_NEW)
>>
>> cachefiles_daemon_read
>> cachefiles_ondemand_daemon_read
>> REQ_A = cachefiles_ondemand_select_req
>> copy_to_user(_buffer, msg, n)
>> xa_erase(&cache->reqs, id)
>> complete(&REQ_A->done)
>> ------ close(fd) ------
>> cachefiles_ondemand_fd_release
>> cachefiles_put_object
>> cachefiles_put_object
>> kmem_cache_free(cachefiles_object_jar, object)
>> REQ_A->object->ondemand->ondemand_id
>> // object UAF !!!
>>
>> When we see the request within xa_lock, req->object must not have been
>> freed yet, so grab the reference count of object before xa_unlock to
>> avoid the above issue.
>>
>> Fixes: 0a7e54c1959c ("cachefiles: resend an open request if the read request's object is closed")
>> Signed-off-by: Baokun Li <libaokun1@huawei.com>
>> Reviewed-by: Jia Zhu <zhujia.zj@bytedance.com>
>> ---
>> fs/cachefiles/ondemand.c | 2 ++
>> include/trace/events/cachefiles.h | 6 +++++-
>> 2 files changed, 7 insertions(+), 1 deletion(-)
>>
>> diff --git a/fs/cachefiles/ondemand.c b/fs/cachefiles/ondemand.c
>> index 56d12fe4bf73..bb94ef6a6f61 100644
>> --- a/fs/cachefiles/ondemand.c
>> +++ b/fs/cachefiles/ondemand.c
>> @@ -336,6 +336,7 @@ ssize_t cachefiles_ondemand_daemon_read(struct cachefiles_cache *cache,
>> xas_clear_mark(&xas, CACHEFILES_REQ_NEW);
>> cache->req_id_next = xas.xa_index + 1;
>> refcount_inc(&req->ref);
>> + cachefiles_grab_object(req->object, cachefiles_obj_get_read_req);
>> xa_unlock(&cache->reqs);
>>
>> if (msg->opcode == CACHEFILES_OP_OPEN) {
>> @@ -355,6 +356,7 @@ ssize_t cachefiles_ondemand_daemon_read(struct cachefiles_cache *cache,
>> close_fd(((struct cachefiles_open *)msg->data)->fd);
>> }
>> out:
>> + cachefiles_put_object(req->object, cachefiles_obj_put_read_req);
>> /* Remove error request and CLOSE request has no reply */
>> if (ret || msg->opcode == CACHEFILES_OP_CLOSE) {
>> xas_reset(&xas);
>> diff --git a/include/trace/events/cachefiles.h b/include/trace/events/cachefiles.h
>> index cf4b98b9a9ed..119a823fb5a0 100644
>> --- a/include/trace/events/cachefiles.h
>> +++ b/include/trace/events/cachefiles.h
>> @@ -33,6 +33,8 @@ enum cachefiles_obj_ref_trace {
>> cachefiles_obj_see_withdrawal,
>> cachefiles_obj_get_ondemand_fd,
>> cachefiles_obj_put_ondemand_fd,
>> + cachefiles_obj_get_read_req,
>> + cachefiles_obj_put_read_req,
> How about cachefiles_obj_[get|put]_ondemand_read, so that it could be
> easily identified as ondemand mode at the first glance?
The ondemand_read tends to confuse whether it's
ondemand_daemon_read or ondemand_data_read. I think it's better
to emphasise the read request, and currently only the ondemand
mode has a cachefiles req.
>> };
>>
>> enum fscache_why_object_killed {
>> @@ -127,7 +129,9 @@ enum cachefiles_error_trace {
>> EM(cachefiles_obj_see_lookup_cookie, "SEE lookup_cookie") \
>> EM(cachefiles_obj_see_lookup_failed, "SEE lookup_failed") \
>> EM(cachefiles_obj_see_withdraw_cookie, "SEE withdraw_cookie") \
>> - E_(cachefiles_obj_see_withdrawal, "SEE withdrawal")
>> + EM(cachefiles_obj_see_withdrawal, "SEE withdrawal") \
>> + EM(cachefiles_obj_get_read_req, "GET read_req") \
>> + E_(cachefiles_obj_put_read_req, "PUT read_req")
> Ditto.
>
>
> Otherwise, LGTM.
>
> Reviewed-by: Jingbo Xu <jefflexu@linux.alibaba.com>
>
Thank you very much for your review!

--
With Best Regards,
Baokun Li