Donald Becker wrote:
> >The fact that there's no standardised API for open-by-inode isn't
> >necessarily a feature. And anyway, even if Jamie's feature got
> >integrated, I'm sure it would be off by default.
>
> We have implemented open-by-inode-number as a kernel module for 2.2.*.
> It approximately follows the "[major:minor:inode]" syntax in the /proc
> psuedo-filesystem. I encourage anyone else implementing a similar
> mechanism to follow the same syntax.
>
...
>
> Most filesystems get *really nervous* when you access an inconsistent inode,
> and some even become unhappy if you merely reference a inode with a zero
> count. We only use it with devices that are marked unwritable, preferably
> with a hardware mechanism or loopback mounted.
>
> Needless to say, any mechanism that so readily cause kernel corruption is
> available only to 'root', so the file security issue never even needs to be
> considered.
My patch is for ext2 only. It adds a new ext2 attribute meaning "this
is an open-by-inode directory". So you create .inode in a filesystem,
chattr it, and then .inode/<number> refers to a specific inode in that
filesystem.
Being ext2-specific, the patch ensures the correct behaviour when you
try opening a non-existent inode: the entry in .inode doesn't exist.
A little care is needed to avoid negative dentries here.
Because this works, it is safe to use on writable filesystems. Access
through .inode is determined by the permissions on that directory as
usual, and of course access to the files and directories themselves is
determined by their permission as usual too.
It seems to work very well, but I don't have a use for it so I've never
given it a thorough test.
My patch is better than Donald Becker's for another reason: you can use
it over NFS ;-)
enjoy,
-- Jamie
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This archive was generated by hypermail 2b29 : Thu Mar 23 2000 - 21:00:30 EST