topic Re: Truly read-only viewer like more or vi? in Operating System - HP-UX

Truly read-only viewer like more or vi?

A. Daniel King_1 — Tue, 18 Jun 2002 14:53:44 GMT

Hi, folks -

Do any of you know of a read-only editor like vi/less/more/rvim/rvi? I guess I don't want an editor at all, but a secure ascii file viewer - without shell escapes or command execution - that otherwise acts like vi. I've been over a few items, but I've found problems with each:

> rview allows saves with a !, i.e., "wq!"
> more allows calling vi (or other editor) with 'v'.
> less ditto.
> Various options on vim including -Z -R, etc. still allow saving files with "wq!"
> pg -r behaves differently than vi (learning curve for my users).

Any ideas are greatly appreciated. HP-UX-only ideas supremely appreciated.

Re: Truly read-only viewer like more or vi?

MANOJ SRIVASTAVA — Tue, 18 Jun 2002 14:57:05 GMT

Hi Daniel

Did you try view , man view .

Manoj Srivastava

Re: Truly read-only viewer like more or vi?

A. Daniel King_1 — Tue, 18 Jun 2002 15:02:48 GMT

view allows "wq!" - and shell escapes.

As part of the charityware package vim, there are rvim and rview, which cut off the shell escapes:

:shell
:!ksh

However, I can still do:

:w!

And overwrite files.

Re: Truly read-only viewer like more or vi?

Paula J Frazer-Campbell — Tue, 18 Jun 2002 15:19:53 GMT

Hi

What about cat | more ??

Paula

Re: Truly read-only viewer like more or vi?

S.K. Chan — Tue, 18 Jun 2002 15:21:03 GMT

Take a look at "mas" from the HPUX porting center. I remembered using it at one point in time. It's relatively simple and the way to run it is just "./mas filename". It brings up X and you have capbility to search within the viewer. I think it does not allow you to modify and save the file (so strictly viewing).

http://hpux.cs.utah.edu/hppd/hpux/Editors/mas-1.0/

Re: Truly read-only viewer like more or vi?

Jeff Schussele — Tue, 18 Jun 2002 15:24:28 GMT

Or just
more /path/to/filename
all by itself.
You can search w/more - just use the "/" as you would in vi as well as go to line numbers using "G".

Jeff

Re: Truly read-only viewer like more or vi?

A. Daniel King_1 — Tue, 18 Jun 2002 15:24:33 GMT

more in the case of 'cat x | more' does prevent file overwriting. This is good.

However, I can still do:

!ksh

I will look at mas. Does it look like vi?

Re: Truly read-only viewer like more or vi?

A. Daniel King_1 — Tue, 18 Jun 2002 15:27:24 GMT

more in the case of 'more x' ...

Try pressing the 'v' key while viewing a file with more. This throws you into your editor - vi typically. This is not the desired behavior.

Re: Truly read-only viewer like more or vi?

A. Daniel King_1 — Tue, 18 Jun 2002 15:29:23 GMT

mas is for GUIs. I neglected to mention that the system I'm on is almost completely terminal based.

Re: Truly read-only viewer like more or vi?

S.K. Chan — Tue, 18 Jun 2002 15:35:00 GMT

Looks like a regular hpterm/xterm window and all it has for it's menu bar (on top) are ..
- find (to find a certain text match)
- find same (not sure what's this)
- copy (presumbly allows you to copy text from this viewer to another window or editor)
- quit
- about
There is no other options for save/edit/cut/paste. It allows you to scroll the window text.

Re: Truly read-only viewer like more or vi?

James R. Ferguson — Tue, 18 Jun 2002 15:35:17 GMT

Hi Daniel:

If you want to defeat the shell escape, you could create a wrapper for 'vi' for your users that sets the SHELL variable to null, exports it and then invokes 'vi':

#/usr/bin/sh
export SHELL=
vi $1
exit 0
#.end

Regards!

...JRF...

Re: Truly read-only viewer like more or vi?

Jeff Schussele — Tue, 18 Jun 2002 15:36:00 GMT

Daniel,

Yep, you're right.
I was not aware of that.
Learned something new today.

A point I would make is that even *if* you find a suitable candidate, there is no substitute for proper dir/file perms. The user can still do
> filename
& poof it's zeroed.
You can keep them out of shells, but it sounds like you don't.
Definitely attack this on both fronts.

Rgds,
Jeff

Re: Truly read-only viewer like more or vi?

MANOJ SRIVASTAVA — Tue, 18 Jun 2002 15:36:45 GMT

Hi Daniel

What about strings filename | more

Manoj Srivastava

Re: Truly read-only viewer like more or vi?

Paula J Frazer-Campbell — Tue, 18 Jun 2002 15:38:24 GMT

Hi

Instead of them viewing the file let them view a copy of it which is discarded afterwards.

so they see:-

view xyz

But in the background:-

cp xyz /tmp/tmpxyz
more /tmp/tmpxyz
rm /tmp/tmpxyz

Just an idea

Paula

Re: Truly read-only viewer like more or vi?

A. Daniel King_1 — Tue, 18 Jun 2002 15:55:16 GMT

Jeff, you are correct - there is no substitute for correct permissions. However, consider the following scenario:

I've got a SUID root program that allows a particular set of users to 'view' a file - otherwise unviewable. I don't want them to be able to change the file, nor escape to a shell.

James, I wish there were a rating for coolness. The null SHELL wrapper is a very good idea. THANK YOU!!! This gets me half-way there.

Now, I can reduce the question to:

Is there an editor which does not allow overwriting with "w!"? I think that this has been covered with the 'cat x | more'.

So, I try a script like:

#!/usr/bin/ksh

cat $1 | SHELL="/dev/null" /usr/bin/more

and I have the results:

'v' produces: "Cannot edit standard input (press RETURN)"

'!ksh' produces: "sh: /dev/null: Execute permission denied."

And I am happy, unless I'm missing some other escape from more. 10 points to whomever has an alternate suggestion or can quantify the answer more concisely!

Re: Truly read-only viewer like more or vi?

Vincent Fleming — Tue, 18 Jun 2002 16:13:42 GMT

I can't think of anything like what you're looking for either... but...

You could always get the source code to 'vi' from a Linux or FreeBSD system (it's downloadable for free), and modify it to disallow saving, shell escapes, etc.

It would be some work, but it might not be as bad as you think. I've done things like that a lot.

Good luck!

Re: Truly read-only viewer like more or vi?

Paula J Frazer-Campbell — Tue, 18 Jun 2002 16:19:01 GMT

Hi

Another option, but will only work on files that are satatic.

When a user selects to view a file by whatever method then take away its write capability:-

So if file is normally :-

-rwxrwxrwx 1 root sys 4492 Dec 15 2000 vm2

As it is selected to view chmod it to:-

-r-xr-xr-x 1 root sys 4492 Dec 15 2000 vm2

And restore it on their exit.

Paula

Re: Truly read-only viewer like more or vi?

Tim D Fulford — Tue, 18 Jun 2002 18:58:36 GMT

If the files are static you could always mount them on a read-only filesystem. This sounds weird but we had a read-only database and mounted the data as above.

Ive even activated whole volume groups as read-only (vgchange -a r ) for sanity checks & stuff.

just a thought

Tim

Re: Truly read-only viewer like more or vi?

A. Daniel King_1 — Tue, 18 Jun 2002 19:11:38 GMT

Paula,

Changing the rights on the file is easily overcome with "w!".

Tim,

Though interesting, the mount solution is highly impractical.

Thanks for the replies.

Re: Truly read-only viewer like more or vi?

Volker Borowski — Tue, 18 Jun 2002 19:12:24 GMT

Hi,
well I think you nearly have everything found you need.
To "more" from a pipe is quite safe, esp. if "vi" is not call-able at all, because it can not read from a pipe.

A point you might keep in mind is that the real problem with "vi" in a suid-root script might not be
:wq!
but
:w/dev/rdsk/c....! -- DO NOT TEST THIS !!!

You should consider a cronjob or some other kind of interface, that "chown"s this file you like to give away to seperate non-root account and call your script with a special suid-accessuser.

Play it safe
Volker