linux-kernel - Re: [PATCH v3] bluetooth: hci_h5: fix memory leak in h5

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Message-ID: <407eed16-ba46-0ba6-544f-d5e820a1ced7@redhat.com>
Date:   Mon, 5 Oct 2020 11:18:44 +0200
From:   Hans de Goede <hdegoede@...hat.com>
To:     Anant Thazhemadam <anant.thazhemadam@...il.com>
Cc:     linux-kernel-mentees@...ts.linuxfoundation.org,
        syzbot+6ce141c55b2f7aafd1c4@...kaller.appspotmail.com,
        Marcel Holtmann <marcel@...tmann.org>,
        Johan Hedberg <johan.hedberg@...il.com>,
        linux-bluetooth@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3] bluetooth: hci_h5: fix memory leak in h5_close

Hi,

On 10/4/20 7:17 AM, Anant Thazhemadam wrote:
> When h5_close() is called and !hu->serdev, h5 is directly freed.
> However, h5->rx_skb is not freed before h5 is freed, which causes
> a memory leak.
> Freeing h5->rx_skb (when !hu->serdev) fixes this memory leak before
> freeing h5.
> 
> Fixes: ce945552fde4 ("Bluetooth: hci_h5: Add support for serdev enumerated devices")
> Reported-by: syzbot+6ce141c55b2f7aafd1c4@...kaller.appspotmail.com
> Tested-by: syzbot+6ce141c55b2f7aafd1c4@...kaller.appspotmail.com
> Signed-off-by: Anant Thazhemadam <anant.thazhemadam@...il.com>
> ---
> Changes in v3:
> 	* Free h5->rx_skb when !hu->serdev, and fix the memory leak
> 	* Do not incorrectly and unnecessarily call serdev_device_close()
> 
> Changes in v2:
> 	* Fixed the Fixes tag
> 
> Hans de Goede also suggested calling h5_reset_rx() on close (for both, !hu->serdev
> and hu->serdev cases).
> However, doing so seems to lead to a null-ptr-dereference error,
>          https://syzkaller.appspot.com/text?tag=CrashReport&x=136a9a5d900000,
> and for this reason, it has not been implemented.
> 
> Instead, directly freeing h5->rx_skb seems to suffice in preventing the memory leak
> reported.
> And since h5 is freed immediately after freeing h5->rx_skb, assigning h5->rx_skb to
> be NULL isn't necessary.
> 
>   drivers/bluetooth/hci_h5.c | 4 +++-
>   1 file changed, 3 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/bluetooth/hci_h5.c b/drivers/bluetooth/hci_h5.c
> index e41854e0d79a..171e55c080ce 100644
> --- a/drivers/bluetooth/hci_h5.c
> +++ b/drivers/bluetooth/hci_h5.c
> @@ -248,8 +248,10 @@ static int h5_close(struct hci_uart *hu)
>   	if (h5->vnd && h5->vnd->close)
>   		h5->vnd->close(h5);
>   
> -	if (!hu->serdev)
> +	if (!hu->serdev){
> +		kfree_skb(h5->rx_skb);
>   		kfree(h5);
> +	}
>   
>   	return 0;
>   }
> 

To fully fix the memleak you also need to add a kfree_skb(h5->rx_skb);
call to the end of h5_serdev_remove(), because in the hu->serdev case
that is where the h5 struct will be free-ed (it is free-ed after that
function exits).

Regards,

Hans