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Re: begone ctrlaltdel!



On Sun, Jul 09, 2000 at 03:13:11PM -0400, Bob Bernstein wrote:
> 
> I had in mind 'none' in the sense of "no one can use Ctrl-Alt-Del." Without
> the -a switch it's available to everyone. (Am I missing something here?)

you could put one of the system account names in /etc/shutdown.allow
say bin who cannot login anyway.  but if commenting out the inittab
line is the same as disabling control-alt-delete that would work just
as well.

> Quite apart from all this, any user who knows the path '/sbin/shutdown' can
> execute it, at least with the permissions shutdown has by default.
> Eliminating this kind of possibility was the reason I started looking into
> the ctrlaltdel business. Which brings me to ask, is there a reason shutdown
> has -rwxr-xr-x perms?

[eb@socrates eb]$ /sbin/shutdown -r now
shutdown: must be root.
[eb@socrates eb]$

so long as a program does not have any s bits set thier is no
advanatage to restricting its permissions.  afterall anyone can
download the sysvinit .deb, extract the shutdown program and execute
it with the same permission as my above example.  

(if you want to see something interesting though try this: fakeroot
/sbin/shutdown -r now)

the only time restricting program permissions is worthwhile is when
there are s bits set or perhaps in the case of the compiler (which is
more difficult to install into the users' userland.) for the compiler
one should change permissions on /usr/lib/gcc as well.

it is also debian policy that all binaries have 0755 permissions when
non-suid for the above reason, and suid binaries must have world read
permission at a minimum (no 4111 or 4711 type permissions) again for
the same reason, anyone can get and read the file out of a .deb.  

-- 
Ethan Benson
http://www.alaska.net/~erbenson/

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