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Message-ID: <8f51f89e-ff27-1131-0d84-84f7821a8cdf@collabora.com>
Date:   Wed, 23 Nov 2022 13:20:28 +0100
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Subject: Re: [PATCH 1/3] usb: gadget: f_hid: fix f_hidg lifetime vs cdev
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To:     John Keeping <john@metanate.com>
Cc:     linux-usb@vger.kernel.org,
        Fabien Chouteau <fabien.chouteau@barco.com>,
        Peter Korsgaard <peter.korsgaard@barco.com>,
        Felipe Balbi <balbi@ti.com>,
        Andrzej Pietrasiewicz <andrzej.p@samsung.com>,
        linux-kernel@vger.kernel.org,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Lee Jones <lee@kernel.org>,
        Alan Stern <stern@rowland.harvard.edu>
References: <20221122123523.3068034-1-john@metanate.com>
 <20221122123523.3068034-2-john@metanate.com>
 <723bd024-121d-dd89-7c39-315e93e49c44@collabora.com>
 <Y34MHCPs1kDObB9m@donbot>
From:   Andrzej Pietrasiewicz <andrzej.p@collabora.com>
In-Reply-To: <Y34MHCPs1kDObB9m@donbot>
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W dniu 23.11.2022 o 13:03, John Keeping pisze:
> On Wed, Nov 23, 2022 at 12:52:24PM +0100, Andrzej Pietrasiewicz wrote:
>> Hi John,
>>
>> W dniu 22.11.2022 o 13:35, John Keeping pisze:
>>> The embedded struct cdev does not have its lifetime correctly tied to
>>> the enclosing struct f_hidg, so there is a use-after-free if /dev/hidgN
>>> is held open while the gadget is deleted.
>>>
>>> This can readily be replicated with libusbgx's example programs (for
>>> conciseness - operating directly via configfs is equivalent):
>>>
>>> 	gadget-hid
>>> 	exec 3<> /dev/hidg0
>>> 	gadget-vid-pid-remove
>>> 	exec 3<&-
>>>
>>> Pull the existing device up in to struct f_hidg and make use of the
>>> cdev_device_{add,del}() helpers.  This changes the lifetime of the
>>> device object to match struct f_hidg, but note that it is still added
>>> and deleted at the same time.
>>>
>>> Fixes: 71adf1189469 ("USB: gadget: add HID gadget driver")
>>> Signed-off-by: John Keeping <john@metanate.com>
>>> ---
>>>    drivers/usb/gadget/function/f_hid.c | 52 ++++++++++++++++-------------
>>>    1 file changed, 28 insertions(+), 24 deletions(-)
>>>
>>> diff --git a/drivers/usb/gadget/function/f_hid.c b/drivers/usb/gadget/function/f_hid.c
>>> index ca0a7d9eaa34..8b8bbeaa27cb 100644
>>> --- a/drivers/usb/gadget/function/f_hid.c
>>> +++ b/drivers/usb/gadget/function/f_hid.c
>>> @@ -71,7 +71,7 @@ struct f_hidg {
>>>    	wait_queue_head_t		write_queue;
>>>    	struct usb_request		*req;
>>> -	int				minor;
>>> +	struct device			dev;
>>>    	struct cdev			cdev;
>>>    	struct usb_function		func;
>>> @@ -84,6 +84,14 @@ static inline struct f_hidg *func_to_hidg(struct usb_function *f)
>>>    	return container_of(f, struct f_hidg, func);
>>>    }
>>> +static void hidg_release(struct device *dev)
>>> +{
>>> +	struct f_hidg *hidg = container_of(dev, struct f_hidg, dev);
>>> +
>>> +	kfree(hidg->set_report_buf);
>>> +	kfree(hidg);
>>> +}
>>> +
>>
>> I assume the above is supposed to free the hidg memory as a result of
>> put_device() and you free two things here ...
>>
>>>    /*-------------------------------------------------------------------------*/
>>>    /*                           Static descriptors                            */
>>> @@ -904,9 +912,7 @@ static int hidg_bind(struct usb_configuration *c, struct usb_function *f)
>>>    	struct usb_ep		*ep;
>>>    	struct f_hidg		*hidg = func_to_hidg(f);
>>>    	struct usb_string	*us;
>>> -	struct device		*device;
>>>    	int			status;
>>> -	dev_t			dev;
>>>    	/* maybe allocate device-global string IDs, and patch descriptors */
>>>    	us = usb_gstrings_attach(c->cdev, ct_func_strings,
>>> @@ -999,21 +1005,11 @@ static int hidg_bind(struct usb_configuration *c, struct usb_function *f)
>>>    	/* create char device */
>>>    	cdev_init(&hidg->cdev, &f_hidg_fops);
>>> -	dev = MKDEV(major, hidg->minor);
>>> -	status = cdev_add(&hidg->cdev, dev, 1);
>>> +	status = cdev_device_add(&hidg->cdev, &hidg->dev);
>>>    	if (status)
>>>    		goto fail_free_descs;
>>> -	device = device_create(hidg_class, NULL, dev, NULL,
>>> -			       "%s%d", "hidg", hidg->minor);
>>> -	if (IS_ERR(device)) {
>>> -		status = PTR_ERR(device);
>>> -		goto del;
>>> -	}
>>> -
>>>    	return 0;
>>> -del:
>>> -	cdev_del(&hidg->cdev);
>>>    fail_free_descs:
>>>    	usb_free_all_descriptors(f);
>>>    fail:
>>> @@ -1244,9 +1240,7 @@ static void hidg_free(struct usb_function *f)
>>>    	hidg = func_to_hidg(f);
>>>    	opts = container_of(f->fi, struct f_hid_opts, func_inst);
>>> -	kfree(hidg->report_desc);
>>> -	kfree(hidg->set_report_buf);
>>> -	kfree(hidg);
>>
>> ... while here 3 things used to be freed. What happens to hidg->report_desc?
> 
> This switched to devm to simplify error handling in hidg_alloc().

Ah, right!

Reviewed-by: Andrzej Pietrasiewicz <andrzej.p@collabora.com>