frame buffers, etc..

[Kartik Subbarao]

In article <KHERA.90Dec4095322 at thneed.cs.duke.edu> khera at thneed.cs.duke.edu (Vick Khera) writes:
>In article <4453 at idunno.Princeton.EDU> subbarao at phoenix.Princeton.EDU (Kartik Subbarao) writes:

>  The other questions is this.  Is there a way to prevent a user from telneting
>  on to the machine while I am using it, and do an xloadimage on my display?
>
>which, to me at least, puts us into the world of X.  to his first
>question, there was already given an answer.  to the second, i
>responded.

Okay - yes you are right. Within the world of X, this is true.

>under SunOS 4.1, when you log in at the console, the /dev/console,
>/dev/fb, as well as all the other graphics display devices are changed
>to be owned by the person logging into the console, with read/write
>permissions tightly controlled.  thus unless you are root or the
>person logged into the console, you cannot simply open /dev/fb and
>scribble on it or read it.  so, once you secure your X server, you are
>pretty safe from people messing up your screen.

Not necessarily the case here. The default case of SunOS 4.1, /dev/fb and 
all of /dev/win's are left owned by root, and are in readable/writable 
mode (i.e rw-rw-rw). 

You can uncomment lines in /etc/fbtab if you want, but that's something
that a normal user can't do. And even  then, there's the problem of 
of non - exclusive resources unlike /dev/audio, where a person can have a 
process continually running which is opening that resource. The argument is
something simliar to tty's. It would be useful to chown those devices, but
thats not necessarily the case and it may not help sometimes.

>in summary, to prevent people from mucking up your screen by using the
>devices directly, use SunOS 4.1.  

Be serious :-) 

				-Kartik

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