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Date:   Wed, 26 Jul 2023 11:49:26 +0200
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Subject: Re: [PATCH] USB: add usbfs ioctl to get specific superspeedplus rates
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To:     Dingyan Li <18500469033@163.com>, Oliver Neukum <oneukum@suse.com>
Cc:     Greg KH <gregkh@linuxfoundation.org>, stern@rowland.harvard.edu,
        sebastian.reichel@collabora.com, linux-usb@vger.kernel.org,
        linux-kernel@vger.kernel.org
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From:   Oliver Neukum <oneukum@suse.com>
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On 26.07.23 11:36, Dingyan Li wrote:
> At 2023-07-26 16:33:22, "Oliver Neukum" <oneukum@suse.com> wrote:
>> On 25.07.23 18:11, Dingyan Li wrote:
>>   
>>> In proc_conninfo_ex(), the number of returned bytes is determined by
>>> the smaller number between sizeof(struct usbdevfs_conninfo_ex) and a
>>> user specified size. So if we only append new members to the end of
>>> struct usbdevfs_conninfo_ex, it won't impact the bytes in the beginning.
>>
>> You have just caused memory corruption in user space by overwriting what
>> was right behind the buffer of the agreed upon size. Or, not much better,
>> caused a segmentation fault.
>>
>> 	Regards
>> 		Oliver
> 
> How come?

Sorry, I misread the check at the start.

> The actual returned bytes must be smaller than or equal to user specified size.
> You can check https://elixir.bootlin.com/linux/v6.5-rc3/source/drivers/usb/core/devio.c#L1493

Yes, we can add. But where is the point?
User space has to be changed to use new sizes.

The problem is not your patch. Add documentation to it and it is fine.
We have a basic issue here. Do we require libusb to use sysfs or not?

	Regards
		Oliver