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From: Hans de Goede <hdegoede@redhat.com>
To: Anant Thazhemadam <anant.thazhemadam@gmail.com>
Cc: syzbot+6ce141c55b2f7aafd1c4@syzkaller.appspotmail.com,
	Johan Hedberg <johan.hedberg@gmail.com>,
	Marcel Holtmann <marcel@holtmann.org>,
	linux-kernel@vger.kernel.org, linux-bluetooth@vger.kernel.org,
	linux-kernel-mentees@lists.linuxfoundation.org
Subject: Re: [Linux-kernel-mentees] [PATCH v3] bluetooth: hci_h5: fix memory leak in h5_close
Date: Tue, 6 Oct 2020 08:30:05 +0200	[thread overview]
Message-ID: <9761cf0c-e2bf-38ea-e1d1-59b481736186@redhat.com> (raw)
In-Reply-To: <93ed51be-97b9-c5b4-8448-d06528a1d1af@gmail.com>

Hi,

On 10/6/20 4:44 AM, Anant Thazhemadam wrote:
> On 05-10-2020 14:48, Hans de Goede wrote:
>> 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).
> 
> Hi Hans,
> 
> I'm not entirely convinced that it might be entirely the best idea to do
> that.
> 
> * The bug detected by syzbot only provides us with reproducer and
> information about this bug (which gets triggered when !hu->serdev).
> Even if like you said, there might be a memory leak unattended to when
> hu->serdev exists, then this might not necessarily be the right place to fix
> it.
> 
> * From what I can see, all the drivers that have modified to provide serdev
> support have different close() mechanisms.
> However, one thing they do have in common (in this context) is that their
> respective serdev_remove() function simply calls hci_uart_unregister_device()
> to unregister the device.
> It is primarily for this reason that I feel adding a kfree_skb() call at the end
> of h5_serdev_remove() might not exactly be the best way we could solve this
> (and since this hasn't been picked up by syzbot yet, there's no way to know if
> this just fixes things or ends up causing unforeseen complications).
> 
> Alternatively, wouldn't freeing h5->rx_skb and assigning it to NULL, for both
> hu->serdev and !hu->serdev cases within h5_close() itself be a better
> approach?

That will indeed also fix the leak in both cases and is more consistent
wrt when the free_skb happens. So this sounds good to me, go for it.

Regards,

Hans



> I've also taken the liberty of testing a patch that does this, and it
> seems to work correctly too. :)
> 
> But then again, I'm not exactly an authority on how this works.
> 
> Thanks,
> Anant
> 

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      reply	other threads:[~2020-10-06  6:30 UTC|newest]

Thread overview: 8+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-10-01 19:43 [Linux-kernel-mentees] [PATCH v2] bluetooth: hci_h5: close serdev device and free hu in h5_close Anant Thazhemadam
2020-10-02 10:22 ` Hans de Goede
2020-10-02 10:55   ` Anant Thazhemadam
2020-10-03 22:07   ` Anant Thazhemadam
2020-10-04  5:17 ` [Linux-kernel-mentees] [PATCH v3] bluetooth: hci_h5: fix memory leak " Anant Thazhemadam
2020-10-05  9:18   ` Hans de Goede
2020-10-06  2:44     ` Anant Thazhemadam
2020-10-06  6:30       ` Hans de Goede [this message]

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