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Subject: Re: [PATCH] wireless: ath9k: hif_usb: fix race condition between
 usb_get_urb() and usb_kill_anchored_urbs()
To:     kvalo@codeaurora.org, davem@davemloft.net, kuba@kernel.org
Cc:     gregkh@linuxfoundation.org, linux-wireless@vger.kernel.org,
        linux-kernel@vger.kernel.org, ath9k-devel@qca.qualcomm.com,
        syzkaller-bugs@googlegroups.com,
        syzbot+89bd486af9427a9fc605@syzkaller.appspotmail.com
References: <20200911071427.32354-1-brookebasile@gmail.com>
From:   Brooke Basile <brookebasile@gmail.com>
Message-ID: <535351e1-90e3-ceb6-3d0a-a445a6d9582c@gmail.com>
Date:   Sat, 19 Sep 2020 22:03:33 -0400
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On 9/11/20 3:14 AM, Brooke Basile wrote:
> Calls to usb_kill_anchored_urbs() after usb_kill_urb() on multiprocessor
> systems create a race condition in which usb_kill_anchored_urbs() deallocates
> the URB before the completer callback is called in usb_kill_urb(), resulting
> in a use-after-free.
> To fix this, add proper lock protection to usb_kill_urb() calls that can
> possibly run concurrently with usb_kill_anchored_urbs().
> 
> Reported-by: syzbot+89bd486af9427a9fc605@syzkaller.appspotmail.com
> Link: https://syzkaller.appspot.com/bug?id=cabffad18eb74197f84871802fd2c5117b61febf
> Signed-off-by: Brooke Basile <brookebasile@gmail.com>
> ---
>   drivers/net/wireless/ath/ath9k/hif_usb.c | 19 +++++++++++++++++++
>   1 file changed, 19 insertions(+)
> 
> diff --git a/drivers/net/wireless/ath/ath9k/hif_usb.c b/drivers/net/wireless/ath/ath9k/hif_usb.c
> index 3f563e02d17d..2ed98aaed6fb 100644
> --- a/drivers/net/wireless/ath/ath9k/hif_usb.c
> +++ b/drivers/net/wireless/ath/ath9k/hif_usb.c
> @@ -449,10 +449,19 @@ static void hif_usb_stop(void *hif_handle)
>   	spin_unlock_irqrestore(&hif_dev->tx.tx_lock, flags);
> 
>   	/* The pending URBs have to be canceled. */
> +	spin_lock_irqsave(&hif_dev->tx.tx_lock, flags);
>   	list_for_each_entry_safe(tx_buf, tx_buf_tmp,
>   				 &hif_dev->tx.tx_pending, list) {
> +		usb_get_urb(tx_buf->urb);
> +		spin_unlock_irqrestore(&hif_dev->tx.tx_lock, flags);
>   		usb_kill_urb(tx_buf->urb);
> +		list_del(&tx_buf->list);
> +		usb_free_urb(tx_buf->urb);
> +		kfree(tx_buf->buf);
> +		kfree(tx_buf);
> +		spin_lock_irqsave(&hif_dev->tx.tx_lock, flags);
>   	}
> +	spin_unlock_irqrestore(&hif_dev->tx.tx_lock, flags);
> 
>   	usb_kill_anchored_urbs(&hif_dev->mgmt_submitted);
>   }
> @@ -762,27 +771,37 @@ static void ath9k_hif_usb_dealloc_tx_urbs(struct hif_device_usb *hif_dev)
>   	struct tx_buf *tx_buf = NULL, *tx_buf_tmp = NULL;
>   	unsigned long flags;
> 
> +	spin_lock_irqsave(&hif_dev->tx.tx_lock, flags);
>   	list_for_each_entry_safe(tx_buf, tx_buf_tmp,
>   				 &hif_dev->tx.tx_buf, list) {
> +		usb_get_urb(tx_buf->urb);
> +		spin_unlock_irqrestore(&hif_dev->tx.tx_lock, flags);
>   		usb_kill_urb(tx_buf->urb);
>   		list_del(&tx_buf->list);
>   		usb_free_urb(tx_buf->urb);
>   		kfree(tx_buf->buf);
>   		kfree(tx_buf);
> +		spin_lock_irqsave(&hif_dev->tx.tx_lock, flags);
>   	}
> +	spin_unlock_irqrestore(&hif_dev->tx.tx_lock, flags);
> 
>   	spin_lock_irqsave(&hif_dev->tx.tx_lock, flags);
>   	hif_dev->tx.flags |= HIF_USB_TX_FLUSH;
>   	spin_unlock_irqrestore(&hif_dev->tx.tx_lock, flags);
> 
> +	spin_lock_irqsave(&hif_dev->tx.tx_lock, flags);
>   	list_for_each_entry_safe(tx_buf, tx_buf_tmp,
>   				 &hif_dev->tx.tx_pending, list) {
> +		usb_get_urb(tx_buf->urb);
> +		spin_unlock_irqrestore(&hif_dev->tx.tx_lock, flags);
>   		usb_kill_urb(tx_buf->urb);
>   		list_del(&tx_buf->list);
>   		usb_free_urb(tx_buf->urb);
>   		kfree(tx_buf->buf);
>   		kfree(tx_buf);
> +		spin_lock_irqsave(&hif_dev->tx.tx_lock, flags);
>   	}
> +	spin_unlock_irqrestore(&hif_dev->tx.tx_lock, flags);
> 
>   	usb_kill_anchored_urbs(&hif_dev->mgmt_submitted);
>   }
> --
> 2.28.0
> 

Hi,

Just wanted to check on the status of this patch, if there's anything 
wrong I'm happy to make it right.
Sorry to bother!

Best,
Brooke Basile