Re: [uml-devel] Exactly what is wanted with hostfs UID/GID operation

[BlaisorBlade <blaisorblade_spam@yahoo.it>]

Answering to a previous message of Jeff Dike
At 03:49, 11 Oct 2003, Jeff Dike wrote:
> doug@easyco.com said:
> > The code itself involves a lot of extra parameters from kernel to user
> >  space as things like the current user aren't propogated down.  I
> > personally think that our current patch set is "100% ugly" and would
> > not  consider posting it as-is.  If people are interested in
> > transparent  numeric UID/GID to hostfs, then I would be happy to clean
> > up what we  have and submit it.
>
> OK, that ain't the way to do it.  Anything that involves passing a parallel
> set of creds through VFS will cause Al Viro to lop my head off.  Since I'm
> somewhat attached to it, I will not propose such a thing, no matter how
> cleaned up it is.
I don't agree. Al Viro doesn't matter here. The only more params to pass are 
from hostfs_kern.c to hostfs_user.c. Stop. Also, since we are in process 
context inside hostfs_kern.c, we can also read current very easily (even if we 
should rely on VFS permission handling as much as possible). By the way, if 
you want to manage the UMSDOS-like db, then you need to pass exactly the same 
params down.
**Security risks!**
Besides, even with the UMSDOS-like db, you still need to avoid as much as 
possible to create root-owned files on the host. It's always a security risk, 
even if it's not that easy to exploit: for instance, let's look at the man 
page of modutils:

By default, modutils will reject attempts to use a  module  that
              is  not  owned by root.
Luckily, you need write access to the /lib/modules path to exploit this, but 
it's not a good thing anyway. So if we remove this possibility, it's a better 
world for all us.
-- 
cat <<EOSIGN
Paolo Giarrusso, aka Blaisorblade
Linux Kernel 2.4.21/2.6.0-test on an i686; Linux registered user n. 292729
EOSIGN




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