linux-kernel - Re: [PATCH v2 resend] media: dvb: usb: Fix WARNING in dib0700_i2c_xfer/usb_submit

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Message-ID: <a2bbdfbf-d7aa-4601-ae1e-18d75d011084@rowland.harvard.edu>
Date: Sat, 29 Mar 2025 10:31:52 -0400
From: Alan Stern <stern@...land.harvard.edu>
To: Wolfram Sang <wsa+renesas@...g-engineering.com>,
	Mauro Carvalho Chehab <mchehab@...nel.org>,
	syzbot <syzbot+c38e5e60d0041a99dbf5@...kaller.appspotmail.com>,
	gregkh@...uxfoundation.org, linux-i2c@...r.kernel.org,
	linux-kernel@...r.kernel.org, linux-usb@...r.kernel.org,
	syzkaller-bugs@...glegroups.com
Subject: Re: [PATCH v2 resend] media: dvb: usb: Fix WARNING in
 dib0700_i2c_xfer/usb_submit_urb

On Sat, Mar 29, 2025 at 07:05:49AM +0100, Wolfram Sang wrote:
> 
> > In the case of dib0700, it was clear from the source code that the 
> > driver uses USB Control transfers to tell the hardware about I2C 
> > messages.  I don't know if other bridges work in the same way.  In 
> > theory a bridge could use USB Bulk transfers instead; they aren't 
> > subject to this restriction on length-0 reads.  Or a bridge could use a 
> > Control read transfer but include extra header material along with the 
> > actual data, so that a length-0 message wouldn't end up generating a 
> > length-0 read.
> 
> Fully understood, thanks for your explanation.
> 
> > So the short answer is that you would need to find someone who really 
> > understands what's going on here -- which I don't.  Sorry.
> 
> No worries. There are only 5 drivers or so, I will manually check if
> they use a control_read and have no own header. Doesn't sound hard.

Good...  Feel free to ask me if you have any questions or need any other 
help.

Alan Stern