From mboxrd@z Thu Jan 1 00:00:00 1970 From: Peter Hurley Subject: Re: [PATCH 1/2] serial: core: Don't drop DTR if system console Date: Tue, 10 Jun 2014 08:30:45 -0400 Message-ID: <5396FA75.8020400@hurleysoftware.com> References: <7EC4C3FDEFF6492F91DEE16AEE0831E6@vanni.it> <1401891371-4946-1-git-send-email-peter@hurleysoftware.com> <20140609140823.6013838d@alan.etchedpixels.co.uk> <53965D53.3010107@hurleysoftware.com> <20140610120136.2c2cb881@alan.etchedpixels.co.uk> Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Return-path: Received: from mailout32.mail01.mtsvc.net ([216.70.64.70]:46031 "EHLO n23.mail01.mtsvc.net" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1750888AbaFJMas (ORCPT ); Tue, 10 Jun 2014 08:30:48 -0400 In-Reply-To: <20140610120136.2c2cb881@alan.etchedpixels.co.uk> Sender: linux-serial-owner@vger.kernel.org List-Id: linux-serial@vger.kernel.org To: One Thousand Gnomes Cc: Greg Kroah-Hartman , linux-serial@vger.kernel.org, linux-kernel@vger.kernel.org, Valerio Vanni On 06/10/2014 07:01 AM, One Thousand Gnomes wrote: >> This patch only affects the line state if the last tty reference is closed >> or the tty is hung up by software (like on controlling process exit). >> In this case, any login session is already dying, and it would not be possible >> to hijack a live session. A successful re-login is still required. > > It breaks the other direction - yes sorry. > >> Notwithstanding what I wrote above, this patch does change behavior >> with remote consoles, which may be unacceptable. > >> For example, if the remote user logs out, the current behavior hangs up >> the modem (if HUPCL), whereas the patch behavior just presents a new >> login prompt. > > which means the modem will probably no longer answer calls. I would expect the vast majority of modems to be configured to hang-up after carrier loss (when the remote user hangs up). I think the more significant impact is that killing the login process (by the sysadmin) wouldn't disconnect a malicious user (but would still force the re-login). I see this as more nuisance value than any realistic DoS. >> So yeah, I agree; this patch should be dropped. > > Possibly we should also fix this the other way in tty_port_shutdown, > which does wrongly skip dtr/rts handling of consoles. > > As far as I can see providing HUPCL is clear the desired console > behaviour for most situations with a remote console link is obtained. I agree that serial core and tty port should handle the console identically, so if the serial core defaults are the expected behavior, then, yes, tty_port_shutdown() should not skip dropping dtr/rts. However, a console on USB tty is much more likely to be local, rather than remote, so changing dtr/rts handling could impact these setups. Since the termios c_cflag is inherited from the console, what about adding new flow control flag decodes to uart_set_options(); eg., 'r' = CRTSCTS | HUPCL /* existing */ 'R' = CRTSCTS | !HUPCL default = !CRTSCTS | HUPCL 'd' = !CRTSCTS | !HUPCL ? Regards, Peter Hurley