[PATCH v3] net: nfc: Fix use-after-free in local_cleanup()

[PATCH v3] net: nfc: Fix use-after-free in local_cleanup()

[Jisoo Jang]

Fix a use-after-free that occurs in kfree_skb() called from
local_cleanup(). When detaching an nfc device, local_cleanup()
called from nfc_llcp_unregister_device() frees local->rx_pending
and cancels local->rx_work. So the socket allocated before
unregister is not set null by nfc_llcp_rx_work().
local_cleanup() called from local_release() frees local->rx_pending
again, which leads to the bug.

Set local->rx_pending to NULL in local_cleanup()

Found by a modified version of syzkaller.

BUG: KASAN: use-after-free in kfree_skb
Call Trace:
 kfree_skb
 local_cleanup
 nfc_llcp_local_put
 llcp_sock_destruct
 __sk_destruct
 sk_destruct
 __sk_free
 sk_free
 llcp_sock_release
 __sock_release
 sock_close
 __fput
 task_work_run
 exit_to_user_mode_prepare
 syscall_exit_to_user_mode
 do_syscall_64
 entry_SYSCALL_64_after_hwframe

Allocate by:
 __alloc_skb
 pn533_recv_response
 __usb_hcd_giveback_urb
 usb_hcd_giveback_urb
 dummy_timer
 call_timer_fn
 run_timer_softirq
 __do_softirq

Freed by:
 kfree_skbmem
 kfree_skb
 local_cleanup
 nfc_llcp_unregister_device
 nfc_unregister_device
 pn53x_unregister_nfc
 pn533_usb_disconnect
 usb_unbind_interface
 device_release_driver_internal
 bus_remove_device
 device_del
 usb_disable_device
 usb_disconnect
 hub_event
 process_one_work
 worker_thread
 kthread
 ret_from_fork


Signed-off-by: Jisoo Jang <jisoo.jang@yonsei.ac.kr>
---
v1->v2: set local->rx_pending to NULL instead move kfree_skb()
v2->v3: fix the bug description

---
 net/nfc/llcp_core.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/net/nfc/llcp_core.c b/net/nfc/llcp_core.c
index 3364caabef8b..a27e1842b2a0 100644
--- a/net/nfc/llcp_core.c
+++ b/net/nfc/llcp_core.c
@@ -157,6 +157,7 @@ static void local_cleanup(struct nfc_llcp_local *local)
 	cancel_work_sync(&local->rx_work);
 	cancel_work_sync(&local->timeout_work);
 	kfree_skb(local->rx_pending);
+	local->rx_pending = NULL;
 	del_timer_sync(&local->sdreq_timer);
 	cancel_work_sync(&local->sdreq_timeout_work);
 	nfc_llcp_free_sdp_tlv_list(&local->pending_sdreqs);
-- 
2.25.1

Re: [PATCH v3] net: nfc: Fix use-after-free in local_cleanup()

[Krzysztof Kozlowski]

On 06/01/2023 07:32, Jisoo Jang wrote:
> Fix a use-after-free that occurs in kfree_skb() called from
> local_cleanup(). When detaching an nfc device, local_cleanup()
> called from nfc_llcp_unregister_device() frees local->rx_pending
> and cancels local->rx_work. So the socket allocated before
> unregister is not set null by nfc_llcp_rx_work().

How nfc_llcp_rx_work() is related to this case? It would if there was a
race condition to which your fix does nothing (so does not close any
race). If there is no race condition, drop the sentence, it is confusing.

If there is a race condition, this is not sufficient fix.

> local_cleanup() called from local_release() frees local->rx_pending
> again, which leads to the bug.
> 
> Set local->rx_pending to NULL in local_cleanup()
> 
> Found by a modified version of syzkaller.
> 
> BUG: KASAN: use-after-free in kfree_skb
> Call Trace:
>  kfree_skb
>  local_cleanup
>  nfc_llcp_local_put
>  llcp_sock_destruct
>  __sk_destruct
>  sk_destruct
>  __sk_free
>  sk_free
>  llcp_sock_release
>  __sock_release
>  sock_close
>  __fput
>  task_work_run
>  exit_to_user_mode_prepare
>  syscall_exit_to_user_mode
>  do_syscall_64
>  entry_SYSCALL_64_after_hwframe

decode_stacktrace.sh could be useful here.

Best regards,
Krzysztof