[Info-vax] disabling a CTRL/Y ast

[Tom Adams]

On Thursday, January 7, 2016 at 11:21:27 AM UTC-5, VAXman- wrote:
> In article <3a583568-e33e-446e-9805-6ea94f9ebf71 at googlegroups.com>, Tom Adams <tadamsmar at gmail.com> writes:
> >On Wednesday, January 6, 2016 at 12:22:06 PM UTC-5, Stephen Hoffman wrote:
> >> On 2016-01-06 16:46:32 +0000, Tom Adams said:
> >> 
> >> > I want to turn ctrl/y into a noop in certain regions of code and turn 
> >> > ctrl/y into an exit in other regions of code.
> >> 
> >> Some background: I've posted more than a few replies here in the 
> >> comp.os.vms newsgroup, specifically discussing the particular 
> >> application in question and its general design, and an unfortunate 
> >> aggregation of the UI and the more critical code paths, and your 
> >> understandable preference to avoid restructuring the application code 
> >> through reworking the existing design to block ^Y from arriving within 
> >> the most critical sections of the code.
> >> 
> >> > I do find that it is necessary to run lib$disable_ctrl at the beginning 
> >> > of the program and lib$enable_ctrl at the end of the program to restore 
> >> > the previous CLI state, but I need to run asts to do the rest.
> >> 
> >> If you want ASTs in some parts of the code and not in others, then 
> >> you're going to have to wrap those sections appropriately.   That's if 
> >> you don't decide to migrate those critical code sections into another 
> >> process context, or related steps.  Because beyond the potential for ^Y 
> >> in these sections and the associated issues you're having with the 
> >> image rundown processing in the absence of an EXIT command, other sorts 
> >> of generic application failures ("bugs") or any arriving $forcex calls 
> >> or such activities can potentially still leave the application in an 
> >> indeterminate state.
> >> 
> >> 
> >> 
> >> -- 
> >> Pure Personal Opinion | HoffmanLabs LLC
> >
> >Here's an example of what I am trying to do that seems to work OK.
> >I guess a forced exit from a bug could leave the CTRL\Y in
> >the disabled state at the CLI instead of the original state.
> >
> >Also, it's possible that someone could define TT to be some terminal
> >other than the login terminal.  VMS leaves all the built-in process
> >logicals that refer to the login terminal vulnerable to redefinition.
> >It may be possible to roll your own safe (executive, no_alias) logical
> >name via a call in syslogin.
> >
> >Also, I still need to cover the cases where this code runs in a context
> >where TT is not defined.
> 
> 	PROGRAM MY_TERMINAL
> 	IMPLICIT NONE
> 
> 	INCLUDE '($DSCDEF)'
> 	INCLUDE '($JPIDEF)'
> 	INCLUDE '(LIB$ROUTINES)'
> 
> 	INTEGER*4 STATUS
> 
> 	RECORD	/DSCDEF1/ TERMINAL
> 
> 	TERMINAL.DSC$W_MAXSTRLEN = 0
> 	TERMINAL.DSC$B_DTYPE = DSC$K_DTYPE_T
> 	TERMINAL.DSC$B_CLASS = DSC$K_CLASS_D
> 	TERMINAL.DSC$A_POINTER = 0
> 
> 	STATUS = LIB$GETJPI(JPI$_TERMINAL,,,,TERMINAL,)
> 	IF (STATUS.AND.1) THEN
> 	  STATUS = LIB$PUT_OUTPUT(TERMINAL)
> 	ENDIF
> 
> 	CALL SYS$EXIT(%VAL(STATUS))
> 	END
> 
> -- 
> VAXman- A Bored Certified VMS Kernel Mode Hacker    VAXman(at)TMESIS(dot)ORG
> 
> I speak to machines with the voice of humanity.

That's better than TT.

But that is also vulnerable to a non-priv user. For instance
if the login terminal is RTA1:  the a non-priv user can define RTA1
thusly:

DEFINE RTA1 LTA180:

Where lta180: is a valid device name.  Calls like SYS$ASSIGN will dutifully
translate RTA1: to LTA180: assign it a channel, and return a
normal status.

Admittedly, it's not very likely that a non-priv user would do that.