Date: Thu, 21 Jul 2016 03:41:36 +1000 (EST) From: Bruce Evans <brde@optusnet.com.au> Cc: freebsd-i386@freebsd.org Subject: Re: [Bug 211246] [syscons] console and ttyv0 competing for keystrokes Message-ID: <20160721013907.T957@besplex.bde.org> In-Reply-To: <bug-211246-10@https.bugs.freebsd.org/bugzilla/> References: <bug-211246-10@https.bugs.freebsd.org/bugzilla/>
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On Wed, 20 Jul 2016 bugzilla-noreply@freebsd.org wrote: > https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=211246 > > Bug ID: 211246 > Summary: [syscons] console and ttyv0 competing for keystrokes > Product: Base System > Version: 10.3-RELEASE > Hardware: i386 > OS: Any > Status: New > Severity: Affects Only Me > Priority: --- > Component: kern > Assignee: freebsd-bugs@FreeBSD.org > Reporter: alexander.klein@physiologie.med.uni-giessen.de > CC: freebsd-i386@FreeBSD.org > CC: freebsd-i386@FreeBSD.org bugzilla inhibits replies not only to itself, but to the Reporter. > On my system, ttyv0 and console are competing for keystrokes on the > ttyv0-screen. This can be seen when logging in under X, immediately issuing > > % xconsole -file /dev/console > > in an xterm, switching to ttyv0 by pressing Ctrl+Alt+F1, and then typing some > text. > > In most cases, the typed text will appear in the Xconsole-window, and even if > this doesn't happen immediately, hammering the keys fast enough with a few > <Ret>s interspersed will usually make at least some characters appear in the > Xconsole-window. > > This might have security implications when parts of login credentials are > redirected. > > As an aside, things written to /dev/console invariably appear on the > ttyv0-screen on my system, but are never passed on to xconsole. This seems to be the expected behaviour. You asked for foot-shooting and got it. This is not a security hole since it requires root privilege. xconsole without -f should use the correct file. If not, try /dev/tty or $(tty). xconsole on /dev/console is like the better-known configuration error of running getty on /dev/console and the physical device underlying /dev/console -- since there is only 1 physical device, i/o must be shared between the open files in some indeterminate way. ioctls also get shared. Except before FreeBSD-8, syscons had magic resulting in not sharing termios, and that mostly worked better. xconsole under FreeBSD-11 with a FreeBSD-~5.2 userland and a FreeBSD-4 ports version of X fails due to permissions problems here, but I saw exactly the same behaviour in the simpler setup of logins on ttyv0 and ttyv1 and a program on ttyv1 grabbing the console using int c = 1; ioctl(0, TIOCCONS, &c);". xconsole with no args works correctly under FreeBSD-~5.2. xconsole -f /dev/console doesn't fail as expected under FreeBSD-~5.2. In fact, it works the same as xconsole with no args: input on ttyv0 is not stolen and is echoed to ttyv0 input on console not tested (xconsole window is output-only) echo to console goes to xconsole window This might be due to the magic non-sharing in syscons before FreeBSD-8. Someone should test the old versions on a serial console without this magic. The tty layer also got signficant plumbing changes for consoles starting in FreeBSD, partly to reduce the need for hacks like syscons' magic. Apparently the magic is needed somewhere. The top layer could with the current restriction to only a physical device for the top level console, but that restriction is wrong, and the changes in FreeBSD increased it. In general, there should be multiple consoles with a different physical device for each, and clearly the settings for things like the line speed on a serial console cannot be shared. Then for each physical device, you might want to keep the settings for things not like the line speed separate. You might even want yet another set of settings for the low level console. The latter set is now hard-coded in some device drivers and the initial state and lock state devices are supposed to be configured to match this state. Bruce
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