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Date:   Tue, 21 May 2019 11:30:16 -0400 (EDT)
From:   Alan Stern <stern@rowland.harvard.edu>
To:     "Eric W. Biederman" <ebiederm@xmission.com>
cc:     linux-usb@vger.kernel.org,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Oliver Neukum <oneukum@suse.com>,
        <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH] signal/usb: Replace kill_pid_info_as_cred with
 kill_pid_usb_asyncio
In-Reply-To: <87zhnfooe6.fsf@xmission.com>
Message-ID: <Pine.LNX.4.44L0.1905211129020.1634-100000@iolanthe.rowland.org>
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On Tue, 21 May 2019, Eric W. Biederman wrote:

> Alan Stern <stern@rowland.harvard.edu> writes:

> >> 	req = (struct usb_ctrlrequest *) buf;
> >> 	req->bRequestType = USB_DIR_IN | USB_TYPE_STANDARD | USB_RECIP_DEVICE;
> >> 	req->bRequest = USB_REQ_GET_DESCRIPTOR;
> >> 	req->wValue = htole16(USB_DT_DEVICE << 8);
> >> 	req->wIndex = htole16(0);
> >> 	req->wLength = htole16(sizeof(buf) - sizeof(*req));
> >
> > In fact, these values are supposed to be in host-endian order, not 
> > necessarily little-endian.  The USB core converts them if necessary.
> 
> Please look again.  In include/uapi/linux/ch9.h those fields are
> explicitly defined as little endian and the code in devio.c for
> USBDEVFS_URB_TYPE_CONTROL treats them as little endian.   Perhaps there
> is a mismatch here but I haven't seen it and I needed this change to get
> the code to work on big endian.

Oops -- you're right.  I was thinking of the USBDEVFS_CONTROL ioctl.  
Sorry for the mistake.

Alan Stern