From: Oliver Neukum <oneukum@suse.com>
To: Simon Arlott <simon@octiron.net>,
Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Oliver Neukum <oneukum@suse.com>,
Jiri Slaby <jirislaby@kernel.org>,
linux-kernel@vger.kernel.org, linux-usb@vger.kernel.org,
linux-serial@vger.kernel.org
Subject: Re: [PATCH] USB: cdc-acm: expose serial close_delay and closing_wait in sysfs
Date: Fri, 25 Aug 2023 01:46:15 +0200 [thread overview]
Message-ID: <f1b001d8-4d6c-8c9d-a90c-7d97294b66b4@suse.com> (raw)
In-Reply-To: <d313a1a9-833e-981e-b9d7-920989458d37@0882a8b5-c6c3-11e9-b005-00805fc181fe.uuid.home.arpa>
On 24.08.23 20:02, Simon Arlott wrote:
> It's not practical to use TIOCGSERIAL from a udev rule. Instead of a
> sysfs attribute (that udev has built-in support for writing) it would
> require a separate compiled process or other non-trivial dependencies
> (e.g. Python) to modify the closing_wait value. There's no shell script
> support for read-modify-write of a complex ioctl struct.
That, however, is a deficiency of udev.
> The ioctl can't be used without opening and closing the tty, which has
> side effects. On open() it'll raise DTR/RTS and activate it. For cdc-acm
> that will indicate to the device that the serial port has been opened
> which will be visible to the software running on the USB device. On
> close() it'll be delayed by the close_delay if any process is currently
> doing a blocking open() and there's no carrier, then the closing_wait
> time if there's been any incomplete transmitted data (by any process).
And that is an issue of the generic serial layer.
> Those two values require CAP_SYS_ADMIN to modify (which is separately
> enforced by many of the tty drivers) so user applications can't change
> them even if they're aware of them.
That is even more damning. Either something is protected by a capability
or it is not. Such a protection must not be circumvented.
Regards
Oliver
next prev parent reply other threads:[~2023-08-24 23:47 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-08-23 20:37 [PATCH] USB: cdc-acm: expose serial close_delay and closing_wait in sysfs Simon Arlott
2023-08-23 21:12 ` [PATCH (v2)] " Simon Arlott
2023-08-24 7:18 ` [PATCH] docs: ABI: sysfs-tty: close times are in hundredths of a second Simon Arlott
2023-08-25 5:33 ` Jiri Slaby
2023-08-27 18:23 ` [PATCH (v2)] docs: ABI: sysfs-tty: close times are in centiseconds Simon Arlott
2023-08-24 8:21 ` [PATCH] USB: cdc-acm: expose serial close_delay and closing_wait in sysfs Oliver Neukum
2023-08-24 14:48 ` Greg Kroah-Hartman
2023-08-24 18:02 ` Simon Arlott
2023-08-24 19:22 ` Greg Kroah-Hartman
2023-08-27 15:36 ` Simon Arlott
2023-08-24 23:46 ` Oliver Neukum [this message]
2023-08-25 1:53 ` Alan Stern
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