Re: [PATCH v3 1/2] wifi: ath9k: fix races between ath9k_wmi_cmd and ath9k_wmi_ctrl_rx

Toke Høiland-Jørgensen
2023-08-08T19:12:21Z

Fedor Pchelkin <pchelkin@ispras.ru> writes:

> Currently, the synchronization between ath9k_wmi_cmd() and
> ath9k_wmi_ctrl_rx() is exposed to a race condition which, although being
> rather unlikely, can lead to invalid behaviour of ath9k_wmi_cmd().
>
> Consider the following scenario:
>
> CPU0 CPU1
>
> ath9k_wmi_cmd(...)
> mutex_lock(&wmi->op_mutex)
> ath9k_wmi_cmd_issue(...)
> wait_for_completion_timeout(...)
> ---
> timeout
> ---
> /* the callback is being processed
> * before last_seq_id became zero
> */
> ath9k_wmi_ctrl_rx(...)
> spin_lock_irqsave(...)
> /* wmi->last_seq_id check here
> * doesn't detect timeout yet
> */
> spin_unlock_irqrestore(...)
> /* last_seq_id is zeroed to
> * indicate there was a timeout
> */
> wmi->last_seq_id = 0
> mutex_unlock(&wmi->op_mutex)
> return -ETIMEDOUT
>
> ath9k_wmi_cmd(...)
> mutex_lock(&wmi->op_mutex)
> /* the buffer is replaced with
> * another one
> */
> wmi->cmd_rsp_buf = rsp_buf
> wmi->cmd_rsp_len = rsp_len
> ath9k_wmi_cmd_issue(...)
> spin_lock_irqsave(...)
> spin_unlock_irqrestore(...)
> wait_for_completion_timeout(...)
> /* the continuation of the
> * callback left after the first
> * ath9k_wmi_cmd call
> */
> ath9k_wmi_rsp_callback(...)
> /* copying data designated
> * to already timeouted
> * WMI command into an
> * inappropriate wmi_cmd_buf
> */
> memcpy(...)
> complete(&wmi->cmd_wait)
> /* awakened by the bogus callback
> * => invalid return result
> */
> mutex_unlock(&wmi->op_mutex)
> return 0
>
> To fix this, update last_seq_id on timeout path inside ath9k_wmi_cmd()
> under the wmi_lock. Move ath9k_wmi_rsp_callback() under wmi_lock inside
> ath9k_wmi_ctrl_rx() so that the wmi->cmd_wait can be completed only for
> initially designated wmi_cmd call, otherwise the path would be rejected
> with last_seq_id check.
>
> Found by Linux Verification Center (linuxtesting.org) with Syzkaller.
>
> Fixes: fb9987d0f748 ("ath9k_htc: Support for AR9271 chipset.")
> Signed-off-by: Fedor Pchelkin <pchelkin@ispras.ru>

Alright, finally took the time to dig into this and convince myself that
the fix if correct. Sorry for taking so long!

Acked-by: Toke Høiland-Jørgensen <toke@toke.dk>