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SubjectRe: [PATCH 0/4] IMA: making i_readcount a first class inode citizen
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On Fri, 2010-11-05 at 12:28 -0400, J. Bruce Fields wrote: 
> On Fri, Nov 05, 2010 at 07:08:06AM -0400, Mimi Zohar wrote:

> > Right, like the ima_file_check(), which is after the __dentry_open().
> > Al, is it possible to move the break_lease() in may_open() to later?
>
> That would still leave a race like:
>
> check count
> bump count
> break lease
> set lease
>
> But we could extend the i_lock to prevent the lease being bumped between
> the two steps on the right-hand side.

The latest i_readcount patchset, i_readcount is atomic and doesn't
require i_lock, at least for IMA. Have to think about this more ....

> At that point I think we'd be done? We're assured the count is still
> zero while the lease is added to the inode, so anyone in the process of
> doing an open has yet to reach the break_lease, which will see the newly
> added lease.
>
> That leaves the problem that leases really should be broken on anything
> that changes the attributes or the dentries pointing to the inode:
> setattr, link, unlink, rename, at least.

For this reason, IMA is now taking i_mutex, preventing file metadata
from changing.

> One approach: add another counter to the inode named disable_leases, and
> have any of those operations do something like:
>
> disable_lease++
> break_lease
> ... do operation ...
> disable_lease--
>
> ?
>
> --b.

lol, getting i_readcount was was hard enough.

Mimi



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