Re: [PATCH] ath9k: Fix potential stack-out-of-bounds write in ath9k_wmi_rsp_callback()

["Toke Høiland-Jørgensen" <toke@toke.dk>]

Minsuk Kang <linuxlovemin@yonsei.ac.kr> writes:

> Fix a stack-out-of-bounds write that occurs in a WMI response callback
> function that is called after a timeout occurs in ath9k_wmi_cmd().
> The callback writes to wmi->cmd_rsp_buf, a stack-allocated buffer that
> could no longer be valid when a timeout occurs. Checking seq_no is
> insufficient as the bug can occur between the timeout and the next WMI
> command. Add wmi->timedout to check whether a timeout occurred.
>
> Found by a modified version of syzkaller.
>
> BUG: KASAN: stack-out-of-bounds in ath9k_wmi_ctrl_rx
> Write of size 4
> Call Trace:
>  memcpy
>  ath9k_wmi_ctrl_rx
>  ath9k_htc_rx_msg
>  ath9k_hif_usb_reg_in_cb
>  __usb_hcd_giveback_urb
>  usb_hcd_giveback_urb
>  dummy_timer
>  call_timer_fn
>  run_timer_softirq
>  __do_softirq
>  irq_exit_rcu
>  sysvec_apic_timer_interrupt
>
> Signed-off-by: Minsuk Kang <linuxlovemin@yonsei.ac.kr>
> ---
>  drivers/net/wireless/ath/ath9k/wmi.c | 5 ++++-
>  drivers/net/wireless/ath/ath9k/wmi.h | 1 +
>  2 files changed, 5 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/net/wireless/ath/ath9k/wmi.c b/drivers/net/wireless/ath/ath9k/wmi.c
> index f315c54bd3ac..f46cbecc12e3 100644
> --- a/drivers/net/wireless/ath/ath9k/wmi.c
> +++ b/drivers/net/wireless/ath/ath9k/wmi.c
> @@ -234,7 +234,8 @@ static void ath9k_wmi_ctrl_rx(void *priv, struct sk_buff *skb,
>  
>  	/* Check if there has been a timeout. */
>  	spin_lock_irqsave(&wmi->wmi_lock, flags);
> -	if (be16_to_cpu(hdr->seq_no) != wmi->last_seq_id) {
> +	if (be16_to_cpu(hdr->seq_no) != wmi->last_seq_id ||
> +	    wmi->timedout) {
>  		spin_unlock_irqrestore(&wmi->wmi_lock, flags);
>  		goto free_skb;
>  	}
> @@ -290,6 +291,7 @@ static int ath9k_wmi_cmd_issue(struct wmi *wmi,
>  
>  	spin_lock_irqsave(&wmi->wmi_lock, flags);
>  	wmi->last_seq_id = wmi->tx_seq_id;
> +	wmi->timedout = false;
>  	spin_unlock_irqrestore(&wmi->wmi_lock, flags);
>  
>  	return htc_send_epid(wmi->htc, skb, wmi->ctrl_epid);
> @@ -341,6 +343,7 @@ int ath9k_wmi_cmd(struct wmi *wmi, enum wmi_cmd_id cmd_id,
>  	if (!time_left) {
>  		ath_dbg(common, WMI, "Timeout waiting for WMI command: %s\n",
>  			wmi_cmd_to_name(cmd_id));
> +		wmi->timedout = true;

Instead of introducing a new 'timedout' field, why not just reset
last_seq_id to 0 here? That way the existing check should trigger the
abort in ath9k_wmi_ctrl_rx()... 

-Toke