Re: localdev and fixed devices

Hi, everybody.

Please check out this branch for a proposed solution:

lp:~gideon/ltsp/ltspfs-trunk-gadi

I introduce an lts.conf parameter called "LOCALDEV_DENY".  With this
parameter, you can deny local devices based upon udevinfo criteria or
combinations of several udevinfo criteria.

Syntax:

LOCALDEV_DENY = "var1:val1,var2:val2,var3:val3+var4:val4"

Which means:

Deny local devices if:  var1 = val1 OR var2 = val2 OR (var3 = val3 AND
var4 = val4)

So, if I want to block all local scsi hard drives, I simply do:

LOCALDEV_DENY = "ID_TYPE:disk+ID_BUS:scsi"

To block all USB devices:

LOCALDEV_DENY = "ID_BUS:usb"

To block all IDE and SCSI hard drives:

LOCALDEV_DENY = "ID_TYPE:disk+ID_BUS:scsi,ID_TYPE:disk+ID_BUS:ide"

This should allow us to drop the "removable" match in the udev rule, and
control to quite a fine degree the devices we wish to block by default,
while allowing the user to override.

Cheers,

-Gadi

On Fri, 2008-09-05 at 12:49 -0700, Vagrant Cascadian wrote:
> On Fri, Sep 05, 2008 at 01:57:46PM +0200, Helmut Lichtenberg wrote:
> > Oliver Grawert schrieb am 27. Aug 2008 um 14:44:55 CEST:
> > > it used to be without checks for removable devices in the original
> > > implementation, due to massive complaints from skolelinux (schools with
> > > dual booted client machines suddenly gave full acccess to the XP
> > > partition to everyone logged in on a thin client) we decided to accept
> > > their hardcoded patch to disable HDDs completely until someone else
> > > comes up with a better solution ... so patches are indeed appreciated
> > > any happily accepted ;)
>  
> > I sent a patch for this problem to the list, but Jim McQuillan redirected me
> > to ltsp-developers. So here's my suggestion:
> 
> > 1. udev must provide all devices, not only removables. Otherwise we could not
> >    select between them via lts.conf.
> 
> until very recently, we didn't have access to lts.conf values from the
> udev scripts (mainly ltspfs_entry). now that we do, it's probably time
> to reconsider this as a configurable value.
> 
> > 2. It seems easier for me not to allow certain devices but to deny them.
> 
> we'll probably want both allow and deny, i'm guessing.
> 
> > 3. Let's restrict it for now for the two traits 'removable' and 'fixed'.
> >    Introduce a variable in lts.conf like this:
> > 
> >    LOCALDEV_DENY = fixed      # possible values: [fixed|removable]
> 
> > 4. Maybe later we can enhance it for certain named devices or partitions. This
> >    needs a more complicated retrieval of udev information and decisions about
> >    the syntax in lts.conf.
> 
> well, it's more complicated than one might think. USB external
> hard-drive cages are not considered removable according to udev, because
> the hard-drive itself is a fixed device, even though it's attached by
> USB, which is clearly removable. i don't know for sure, but there may be
> other cases like that (firewire devices?).
> 
> maybe this would be why we need a corresponding LOCALDEV_ALLOW.
>  
> > To implement this for the new ltspfs-trunk, Oliver pointed to, there are only
> > two new functions for ltspfs_entry: is_removable() and is_denied().
> > 
> > I've put a first implementation into a shell script, where you can test it
> > easily. 
> 
> the basic idea looks reasonable(if we can account for the
> above-mentioned issues), but i'd prefer to see a patch against
> ltspfs-trunk instead of an example script, if possible. this would make
> it easier to test and see how it would be used.
> 
> live well,
>   vagrant
> 
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-- 
Gideon Romm <[email protected]>


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