From: Oliver Neukum <oneukum@suse.com>
To: "H. Peter Anvin" <hpa@zytor.com>, Oliver Neukum <oneukum@suse.com>
Cc: linux-usb@vger.kernel.org, linux-kernel@vger.kernel.org,
gregkh@linuxfoundation.org, Jiri Slaby <jirislaby@kernel.org>,
linux-serial@vger.kernel.org
Subject: Re: USB cdc-acm driver: break and command
Date: Wed, 16 Jul 2025 10:29:27 +0200 [thread overview]
Message-ID: <fa20ab91-5ebf-427d-b938-31ea6fb945cf@suse.com> (raw)
In-Reply-To: <ce54ae11-72bb-4ac7-980b-c1cbc798a209@zytor.com>
On 15.07.25 23:00, H. Peter Anvin wrote:
> Hi,
>
> I noticed looking at the CDC-ACM driver that it uses the assert/local delay/deassert method of sending BREAK. Given that the CDC model has a delay specifier in the command packet, is there any reason not to set TTY_DRIVER_HARDWARE_BREAK and sending only one packet?
1. The existing code is tested and usually works.
2. The locking goes away. I have no idea what happens if you are
sending a second break while a break is still going on.
> I'm also wondering if it would make sense to support the SEND_ENCAPSULATED_COMMAND and GET_ENCAPSULATED_RESPONSE commands, presumably via an ioctl(). I'm not 100% sure because I'm not sure there aren't potential security issues.
Well, one of the purposes of the CDC-ACM driver is to hide that
you are talking to a USB device.
In theory we could do that. I don't quite see the value.
Sending arbitrary data from user space to a control endpoint
does not make me happy.
HTH
Oliver
next prev parent reply other threads:[~2025-07-16 8:29 UTC|newest]
Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top
2025-07-15 21:00 USB cdc-acm driver: break and command H. Peter Anvin
2025-07-16 6:58 ` Greg KH
2025-07-16 8:29 ` Oliver Neukum [this message]
2025-07-16 15:06 ` H. Peter Anvin
2025-07-16 16:17 ` Oliver Neukum
2025-07-16 17:30 ` H. Peter Anvin
2025-07-17 11:32 ` Oliver Neukum
2025-07-16 17:49 ` H. Peter Anvin
2025-07-17 11:28 ` Oliver Neukum
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