linux-kernel - Re: Memory leak in ath9k_hif_usb_dealloc_tx

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Message-ID: <YGQWf1lP4ZOUFiG5@kroah.com>
Date:   Wed, 31 Mar 2021 08:28:15 +0200
From:   Greg KH <gregkh@...uxfoundation.org>
To:     Pavel Skripkin <paskripkin@...il.com>
Cc:     brookebasile@...il.com, ath9k-devel@....qualcomm.com,
        davem@...emloft.net, kuba@...nel.org, kvalo@...eaurora.org,
        linux-kernel@...r.kernel.org, linux-wireless@...r.kernel.org,
        syzbot+89bd486af9427a9fc605@...kaller.appspotmail.com,
        syzkaller-bugs@...glegroups.com
Subject: Re: Memory leak in ath9k_hif_usb_dealloc_tx_urbs()

On Tue, Mar 30, 2021 at 10:36:52PM +0300, Pavel Skripkin wrote:
> Hi!
> 
> I did some debugging on this
> https://syzkaller.appspot.com/bug?id=3ea507fb3c47426497b52bd82b8ef0dd5b6cc7ee
> and, I believe, I recognized the problem. The problem appears in case of
> ath9k_htc_hw_init() fail. In case of this fail all tx_buf->urb krefs will be
> initialized to 1, but in free function:
> 
> static void ath9k_hif_usb_dealloc_tx_urbs(struct hif_device_usb *hif_dev)
> 
> ....
> 
> static void ath9k_hif_usb_dealloc_tx_urbs(struct hif_device_usb *hif_dev)
> {
>     ...
> 	list_for_each_entry_safe(tx_buf, tx_buf_tmp,
> 				 &hif_dev->tx.tx_buf, list) {
> 		usb_get_urb(tx_buf->urb);
> 		...
> 		usb_free_urb(tx_buf->urb);
> 		...
> 		}
> 
> Krefs are incremented and then decremented, that means urbs won't be freed.
> I found your patch and I can't properly understand why You added usb_get_urb(tx_buf->urb).
> Can You explain please, I believe this will help me or somebody to fix this ussue :)

I think almost everyone who has looked into this has given up due to the
mess of twisty-passages here with almost no real-world benefits for
unwinding them :)

Good luck!

greg k-h