linux-kernel - Re: [PATCH v4 1/3] Bluetooth: Fix possible race with userspace of sysfs isoc

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Message-ID: <CADg1FFdez0OdNDPRFPFxNHL_JcKmHE6KNxnYvt4sK7i+Uw6opA@mail.gmail.com>
Date: Thu, 13 Feb 2025 19:57:15 +0800
From: Hsin-chen Chuang <chharry@...gle.com>
To: Greg KH <gregkh@...uxfoundation.org>, luiz.dentz@...il.com
Cc: linux-bluetooth@...r.kernel.org, 
	chromeos-bluetooth-upstreaming@...omium.org, 
	Hsin-chen Chuang <chharry@...omium.org>, "David S. Miller" <davem@...emloft.net>, 
	Eric Dumazet <edumazet@...gle.com>, Jakub Kicinski <kuba@...nel.org>, 
	Johan Hedberg <johan.hedberg@...il.com>, Marcel Holtmann <marcel@...tmann.org>, 
	Paolo Abeni <pabeni@...hat.com>, Simon Horman <horms@...nel.org>, Ying Hsu <yinghsu@...omium.org>, 
	linux-kernel@...r.kernel.org, netdev@...r.kernel.org
Subject: Re: [PATCH v4 1/3] Bluetooth: Fix possible race with userspace of
 sysfs isoc_alt

The btusb driver data is allocated by devm_kzalloc and is
automatically freed on driver detach, so I guess we don't have
anything to do here.
Or perhaps we should move btusb_disconnect's content here? Luiz, what
do you think?

On Thu, Feb 13, 2025 at 6:01 PM Greg KH <gregkh@...uxfoundation.org> wrote:
>
> On Thu, Feb 13, 2025 at 11:43:59AM +0800, Hsin-chen Chuang wrote:
> > From: Hsin-chen Chuang <chharry@...omium.org>
> >
> > Expose the isoc_alt attr with device group to avoid the racing.
> >
> > Now we create a dev node for btusb. The isoc_alt attr belongs to it and
> > it also becomes the parent device of hci dev.
> >
> > Fixes: b16b327edb4d ("Bluetooth: btusb: add sysfs attribute to control USB alt setting")
> > Signed-off-by: Hsin-chen Chuang <chharry@...omium.org>
> > ---
> >
> > Changes in v4:
> > - Create a dev node for btusb. It's now hci dev's parent and the
> >   isoc_alt now belongs to it.
> > - Since the changes is almost limitted in btusb, no need to add the
> >   callbacks in hdev anymore.
> >
> > Changes in v3:
> > - Make the attribute exported only when the isoc_alt is available.
> > - In btusb_probe, determine data->isoc before calling hci_alloc_dev_priv
> >   (which calls hci_init_sysfs).
> > - Since hci_init_sysfs is called before btusb could modify the hdev,
> >   add new argument add_isoc_alt_attr for btusb to inform hci_init_sysfs.
> >
> >  drivers/bluetooth/btusb.c        | 98 +++++++++++++++++++++++++-------
> >  include/net/bluetooth/hci_core.h |  1 +
> >  net/bluetooth/hci_sysfs.c        |  3 +-
> >  3 files changed, 79 insertions(+), 23 deletions(-)
> >
> > diff --git a/drivers/bluetooth/btusb.c b/drivers/bluetooth/btusb.c
> > index 1caf7a071a73..cb3db18bb72c 100644
> > --- a/drivers/bluetooth/btusb.c
> > +++ b/drivers/bluetooth/btusb.c
> > @@ -920,6 +920,8 @@ struct btusb_data {
> >       int oob_wake_irq;   /* irq for out-of-band wake-on-bt */
> >
> >       struct qca_dump_info qca_dump;
> > +
> > +     struct device dev;
> >  };
> >
> >  static void btusb_reset(struct hci_dev *hdev)
> > @@ -3693,6 +3695,9 @@ static ssize_t isoc_alt_store(struct device *dev,
> >       int alt;
> >       int ret;
> >
> > +     if (!data->hdev)
> > +             return -ENODEV;
> > +
> >       if (kstrtoint(buf, 10, &alt))
> >               return -EINVAL;
> >
> > @@ -3702,6 +3707,34 @@ static ssize_t isoc_alt_store(struct device *dev,
> >
> >  static DEVICE_ATTR_RW(isoc_alt);
> >
> > +static struct attribute *btusb_sysfs_attrs[] = {
> > +     NULL,
> > +};
> > +ATTRIBUTE_GROUPS(btusb_sysfs);
> > +
> > +static void btusb_sysfs_release(struct device *dev)
> > +{
> > +     // Resource release is managed in btusb_disconnect
>
> That is NOT how the driver model works, do NOT provide an empty
> release() function just to silence the driver core from complaining
> about it.
>
> If for some reason the code thinks it is handling devices differently
> than it should be, fix that instead.
>
> thanks,
>
> greg k-h

-- 
Best Regards,
Hsin-chen