As I've been playing around with the issue more, it seems to be a general
issue with Ctrl-C trapping within the Mystic client. When I run any of the following examples from a Bash prompt, Ctrl-C is trapped:

trap '' 2;frotz seastalk.dat
trap '' 2;nudoku
trap '' 2;znake

But if I run the exact same command from a Mystic menu via (DD) or (D3) Ctrl-C breaks out to a command line.

Now this is interesting:

If I run a trap before launching Mystic:

trap '' 2;./mystic

then Ctrl-C *IS* trapped and I can no longer break out to a command line.

From the playing around I've been doing, trapping Ctrl-C before running the Mystic client makes it possible to securely run pretty much any Linux console app as a door.

Any way I can do this?

--nathanael
*HUMONGOUS* BBS - jenandcal.familyds.org:2323

--- Mystic BBS v1.12 A41 2018/12/27 (Raspberry Pi/32)
* Origin: *HUMONGOUS* BBS (21:4/123)

Any way I can do this?

Hey, nathanael!

(I'm talking to myself :-) )

Here's what I've done: I renamed the mystic command to _mystic, then
replaced it with a bash script called 'mystic':

#!/bin/bash
cd /mystic
trap '' 2
./_mystic "$*"

And voila! Ran across the street to 7-11, was still able to log in remotely, and it appears Ctrl-C is now being trapped.

I'll continue testing before I go live with this, but am I missing anything obvious? Like a way to natively trap Ctrl-C in Mystic, or security concerns?

--nathanael
*HUMONGOUS* BBS - jenandcal.familyds.org:2323

--- Mystic BBS v1.12 A41 2018/12/27 (Raspberry Pi/32)
* Origin: *HUMONGOUS* BBS (21:4/123)

#!/bin/bash
cd /mystic
trap '' 2
./_mystic "$*"

And voila! Ran across the street to 7-11, was still able to log in remotely, and it appears Ctrl-C is now being trapped.

I'll continue testing before I go live with this, but am I missing anything obvious? Like a way to natively trap Ctrl-C in Mystic, or security concerns?

Unfortunately, there is a race condition here....

You execute `trap` to trap signal number 2 (SIGINT,
presumably...the thing the tty driver generates if
you hit ^C) but nothing prevents SIGINT from being
delivered to your process *before* the `trap` command
is interpreted by the shell.

Also, there are a lot of other signals you might
want to trap: SIGQUIT (generated by '^\' usually),
SIGTSTP (^Z) etc.

In general, trying to trap signals in a shell script
is rough. It's better to have the forking process
do it for you.

--- Mystic BBS v1.12 A39 2018/04/21 (Windows/32)
* Origin: Black Flag <ACiD Telnet HQ> blackflagbbs.com (21:1/112)

Unfortunately, there is a race condition here....

True, of course. Without a way to trap from within Mystic or its door
process, however, this is the best I could come up with.

Also, there are a lot of other signals you might

Thanks for the remind about ^\. I'm now trapping SIGINT(2) SIGQUIT(3) SIGTERM(15) and SIGTSTP(20). I think that covers everything a user could do from the keyboard.

--nathanael
*HUMONGOUS* BBS - jenandcal.familyds.org:2323

--- Mystic BBS v1.12 A41 2018/12/27 (Raspberry Pi/32)
* Origin: *HUMONGOUS* BBS (21:4/123)

SIGTERM(15) and SIGTSTP(20). I think that covers everything a user could do from the keyboard.

Not really. Work in an office environment and you'll be suprised what a
user can do from the keyboard......

--- MagickaBBS v0.12alpha (Linux/armv7l)
* Origin: Fusion ~ MagickaBBS (21:4/132.1)

:-) Yeah, I know. I did my time in IT desk support, including a few years of tech support for MS. Even today I still provide tech support for my mother -- who (true story!) once tried to type on the keyboard with the mouse.

But in this case I'm only thinking as far as "accidentally break out of a
door in unanticipated ways". So long as they stay inside the door, I'm not worried.

--nathanael
*HUMONGOUS* BBS - jenandcal.familyds.org:2323

--- Mystic BBS v1.12 A41 2018/12/27 (Raspberry Pi/32)
* Origin: *HUMONGOUS* BBS (21:4/123)

But in this case I'm only thinking as far as "accidentally break out of a door in unanticipated ways". So long as they stay inside the door, I'm
not worried.

Like when they spill an entire cup of coffee on the keyboard then spend
20 minutes mashing every button with a tea towel trying to clean it all
up not realizing they are actually typing tons of garbage into a database
or google search :P

--- MagickaBBS v0.12alpha (Linux/armv7l)
* Origin: Fusion ~ MagickaBBS (21:4/132.1)

On 21 Jan 2019, nathanael pondered and said...

Any way I can do this?

Hey, nathanael!

(I'm talking to myself :-) )

Oh no, he's talking to himself...

Best, Paul

--- E:avon@bbs.nz ------ W:bbs.nz ---
--- K:keybase.io/avon --------------

--- Mystic BBS v1.12 A42 2018/12/30 (Windows/32)
* Origin: Agency BBS | Dunedin, New Zealand | agency.bbs.nz (21:1/101)

On 21 Jan 2019, Avon pondered and said...

On 21 Jan 2019, nathanael pondered and said...

Any way I can do this?

Hey, nathanael!

(I'm talking to myself :-) )

Oh no, he's talking to himself...

Yeah I fear it's worse than we first thought :)

Best, Paul

--- E:avon@bbs.nz ------ W:bbs.nz ---
--- K:keybase.io/avon --------------

--- Mystic BBS v1.12 A42 2018/12/30 (Windows/32)
* Origin: Agency BBS | Dunedin, New Zealand | agency.bbs.nz (21:1/101)

Any way I can do this?

Hey, nathanael!

(I'm talking to myself :-) )

Oh no, he's talking to himself...

As long as he doesn't answer himself, he's ok... lol!

Fireball

--- Mystic BBS v1.12 A41 2018/12/27 (Linux/64)
* Origin: Fireball Express!!! Mystic Edition (21:4/145)

up not realizing they are actually typing tons of garbage into a database or google search :P

Databases? Young'uns these days. Back in my day "databases" meant notes Scotch-taped to the fridge.

+-----------------------+ +-------+
| *:H:U:M:O:N:G:O:U:S:* | | B:B:S | nathanael : jenandcal.familyds.org:2323 +-----------------------+ +-------+

--- Mystic BBS v1.12 A41 2018/12/27 (Raspberry Pi/32)
* Origin: *HUMONGOUS* BBS (21:4/123)

Nonsense. No, I'm not.

Yes, you are.

+-----------------------+ +-------+
| *:H:U:M:O:N:G:O:U:S:* | | B:B:S | nathanael : jenandcal.familyds.org:2323 +-----------------------+ +-------+

--- Mystic BBS v1.12 A41 2018/12/27 (Raspberry Pi/32)
* Origin: *HUMONGOUS* BBS (21:4/123)

Yes, you are.

You're just jealous 'cause Mom always like me best.

+-----------------------+ +-------+
| *:H:U:M:O:N:G:O:U:S:* | | B:B:S | nathanael : jenandcal.familyds.org:2323 +-----------------------+ +-------+

--- Mystic BBS v1.12 A41 2018/12/27 (Raspberry Pi/32)
* Origin: *HUMONGOUS* BBS (21:4/123)

True, of course. Without a way to trap from within Mystic or its door process, however, this is the best I could come up with.

Yeah.... Without support in the spawning process, you'll always
have a race. Something you might do is spawn a wrapper (written
in "C" or a similarly low-level language) that sets up signal
handlers and then exec's the real door program. Then, if that
C (or whatever) program takes a signal before the exec, it just
executes the default signal action, which is hopefully harmless
(but not, e.g., invoking a shell or something).

Thanks for the remind about ^\. I'm now trapping SIGINT(2) SIGQUIT(3) SIGTERM(15) and SIGTSTP(20). I think that covers everything a user could do from the keyboard.

Not a problem. A quick grep through tty.c in the kernel
running on my machine shows the driver generating the
following signals:

SIGINT (^C)
SIGQUIT (^\)
SIGINFO (^T)
SIGTSTP (^Z)
SIGHUP (sent to processes on revoke(2) or close())
SIGWINCH (Remote window size change)
SIGTTIN (TTY read from background process)
SIGTTOU (controlling terminal action from background process)
SIGIO (async IO; TTY device ready for IO)

I might have missed one, but this list looks reasonable.
Most are pretty innocuous.

SIGTTOU is kind of interesting; it's when a background
process tries to do something like an ioctl() on the terminal
device to put it into raw mode.

--- Mystic BBS v1.12 A39 2018/04/21 (Windows/32)
* Origin: Black Flag <ACiD Telnet HQ> blackflagbbs.com (21:1/112)

Thanks for the remind about ^\. I'm now trapping SIGINT(2) SIGQUIT(3) SIGTERM(15) and SIGTSTP(20). I think that covers everything a user could do from the keyboard.

If you trap some of these you may interfere with the operating system trying to work with Mystic's processes though. SIGTERM, SIGHUP and SIGPIPE are all trapped by Mystic itself, everything else is ignored.

I am pretty sure I trap CTRL-C in Windows (not for doors but Mystic itself) but its been so long I'd have to go look at the code to see what I am doing in Linux. Maybe the solution is that I add whatever it is that you need to do into Mystic.

I'll have to set up a door or something that mimics your situation for
testing purposes, but let me make sure I understand the issue:

You want to run a text-based non-BBS program as a door but users are able to CTRL-C out of it and end up on a bash shell. Is that correct?

--- Mystic BBS v1.12 A42 2018/12/31 (Windows/32)
* Origin: Sector 7 [Mystic BBS WHQ] (21:1/108)

You want to run a text-based non-BBS program as a door but users are
able to CTRL-C out of it and end up on a bash shell. Is that correct?

Correct.

I've presently got BSD Games, for example, set up as doors, but they can all
be ^C-ed. Trapping SIGINT in a bash wrapper script before running the mystic client fixes it. In theory, as tenser mentioned, it's vulnerable to a racing condition (though I suspect most folk type too slowly to make it a practical concern).

+-----------------------+ +-------+
| *:H:U:M:O:N:G:O:U:S:* | | B:B:S | nathanael : jenandcal.familyds.org:2323 +-----------------------+ +-------+

--- Mystic BBS v1.12 A41 2018/12/27 (Raspberry Pi/32)
* Origin: *HUMONGOUS* BBS (21:4/123)

trying to work with Mystic's processes though. SIGTERM, SIGHUP and SIGPIPE are all trapped by Mystic itself, everything else is ignored.

ATM I'm trapping SIGINT, SIGQUIT SIGTERM and SIGTSTP -- basically, ^C, ^Z, ^T and ^\. Most of the BSD games still respond to ^C, I just end up back in
Mystic instead of a command line.

In any case, my menu entries are pretty simple:

(DD) Exec external program
clear;adventure

+-----------------------+ +-------+
| *:H:U:M:O:N:G:O:U:S:* | | B:B:S | nathanael : jenandcal.familyds.org:2323 +-----------------------+ +-------+

--- Mystic BBS v1.12 A41 2018/12/27 (Raspberry Pi/32)
* Origin: *HUMONGOUS* BBS (21:4/123)

Correct.

I've presently got BSD Games, for example, set up as doors, but they can all be ^C-ed. Trapping SIGINT in a bash wrapper script before running
the mystic client fixes it. In theory, as tenser mentioned, it's vulnerable to a racing condition (though I suspect most folk type too slowly to make it a practical concern).

Thanks! I'll have to experiment with it and see what code I already have in place and maybe I can build off of it to do something to prevent this.

I know that Mystic already does a "watchdog" on the process while its running, so for example if the connection is dropped by the user and Mystic is executing something that isn't a BBS door capable of detecting it, then Mystic will send a SIGTERM to the subprocess the user is in and wait until it returns.

Maybe I can build something into that system to prevent SIGINT on the child process.

--- Mystic BBS v1.12 A42 2019/01/23 (Windows/32)
* Origin: Sector 7 [Mystic BBS WHQ] (21:1/108)

trying to work with Mystic's processes though. SIGTERM, SIGHUP and SIGPIPE are all trapped by Mystic itself, everything else is ignored.

ATM I'm trapping SIGINT, SIGQUIT SIGTERM and SIGTSTP -- basically, ^C,
^Z, ^T and ^\. Most of the BSD games still respond to ^C, I just end up back in Mystic instead of a command line.

In any case, my menu entries are pretty simple:
(DD) Exec external program
clear;adventure

Perfect thanks for the clarification. I've added it to my list of things to look into and I consider this to be a pretty serious thing to address so I'll try to work on it the next time I have a good chunk of time to do some coding/testing.

--- Mystic BBS v1.12 A42 2019/01/23 (Windows/32)
* Origin: Sector 7 [Mystic BBS WHQ] (21:1/108)

Maybe I can build something into that system to prevent SIGINT on the child process.

I'm not a programmer, but sometimes I want to send a Ctrl-C to the door program. For most of the BSD Games, for example, it's the only way to exit out of them.

If I'm not trapping SIGINT, typing Ctrl-C inside a BSD game running in a door shuts down the game *and* drops me to a command line. Running fg will foreground Mystic again.

If I am trapping SIGINT typing Ctrl-C still shuts down the game, but returns me to Mystic.

+=======================+ +=========+ ---------------------------------------
| *:H:U:M:O:N:G:O:U:S:* | | :B:B:S: | nathanael : jenandcal.familyds.org:2323 +=======================+ +=========+ ---------------------------------------

--- Mystic BBS v1.12 A41 2018/12/27 (Raspberry Pi/32)
* Origin: *HUMONGOUS* BBS (21:4/123)