linux-kernel - Re: [External] [PATCH 04/12] cachefiles: fix slab-use-after-free in cachefiles_ondemand_daemon

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Date: Thu, 25 Apr 2024 11:42:28 +0800
From: Jia Zhu <zhujia.zj@...edance.com>
To: libaokun@...weicloud.com, netfs@...ts.linux.dev
Cc: dhowells@...hat.com, jlayton@...nel.org, jefflexu@...ux.alibaba.com,
 linux-erofs@...ts.ozlabs.org, linux-fsdevel@...r.kernel.org,
 linux-kernel@...r.kernel.org, Baokun Li <libaokun1@...wei.com>,
 zhujia.zj@...edance.com
Subject: Re: [External] [PATCH 04/12] cachefiles: fix slab-use-after-free in
 cachefiles_ondemand_daemon_read()



在 2024/4/24 11:39, libaokun@...weicloud.com 写道:
> From: Baokun Li <libaokun1@...wei.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@...wei.com>

Reviewed-by: Jia Zhu <zhujia.zj@...edance.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,
>   };
>   
>   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")
>   
>   #define cachefiles_coherency_traces					\
>   	EM(cachefiles_coherency_check_aux,	"BAD aux ")		\