Re: [RFC][PATCH] ensure i_ino uniqueness in filesystems without permanent inode numbers (via pointer conversion)

[Dave Kleikamp <shaggy@linux.vnet.ibm.com>]

On Fri, 2006-11-17 at 09:48 -0500, Jeff Layton wrote:
> On Fri, 2006-11-17 at 07:24 -0700, Matthew Wilcox wrote:
> > I *think* the xor mask is mere obfuscation.  It looks likely that you can
> > recover it with a little bit of trial and error.  If you can force the
> > filesystem to hand you back new inodes quickly such that there is a high
> > probability you get consecutive allocations, you'll get a sequence which
> > would be spaced 700-odd bytes apart, except that it's been xored.  Since
> > you know it's incrementing, if you see the sequence decrease, you'll
> > know that was a 1 in that bit.
> 
> I think you're right, the addresses would often be sequential, so this
> is probably crackable. 

Wouldn't you only be able to only crack a few of the low-order bits due
to a cluster of inodes being sequential?  I don't think you'd be able
crack enough of it to be useful.  You may be able to determine where
some inodes are relative to others, but I don't think you'd be able to
point the their location in memory.  I don't know anything about crypto,
so I could be wrong.

> I'll look over the md5 routines when I get the
> chance, though if someone more cryptographically inclined than I has a
> different suggestion, I'd love to hear it.
> -- Jeff

Shaggy
-- 
David Kleikamp
IBM Linux Technology Center