Re: [PATCH v5 23/23] integrity: Switch from rbtree to LSM-managed blob for integrity_iint_cache

[Mimi Zohar <zohar@linux.ibm.com>]

On Wed, 2023-12-06 at 14:10 +0100, Roberto Sassu wrote:
> On Mon, 2023-12-04 at 14:26 +0100, Roberto Sassu wrote:

...
> > If the result of this patch set should be that IMA and EVM become
> > proper LSMs without the shared integrity layer, instead of collapsing
> > all changes in this patch set, I think we should first verify if IMA
> > and EVM can be really independent. Once we guarantee that, we can
> > proceed making the proper LSMs.
> > 
> > These are the changes I have in mind:
> > 
> > 1) Fix evm_verifyxattr(), and make it work without integrity_iint_cache
> > 2) Remove the integrity_iint_cache parameter from evm_verifyxattr(),
> >    since the other callers are not going to use it
> 
> Ehm, I checked better.
> 
> integrity_inode_get() is public too (although it is not exported). So,
> a caller (not IMA) could do:
> 
> iint = integrity_inode_get(inode);
> status = evm_verifyxattr(..., iint);
> 
> However, it should not call integrity_inode_free(), which is also in
> include/linux/integrity.h, since this is going to be called by
> security_inode_free() (currently).

Calling integrity_inode_free() directly would release the iint early.  
As a result, IMA would then need to re-allocate it on next access. 
Other than impacting IMA's performance, is this a problem?

> > 3) Create an internal function with the original parameters to be used
> >    by IMA
> > 4) Introduce evm_post_path_mknod(), which similarly to
> >    ima_post_path_mknod(), sets IMA_NEW_FILE for new files
> 
> I just realized that also this is changing the current behavior.
> 
> IMA would clear IMA_NEW_FILE in ima_check_last_writer(), while EVM
> wouldn't (unless we implement the file_release hook in EVM too).

True

Mimi

> > 5) Add hardcoded call to evm_post_path_mknod() after
> >    ima_post_path_mknod() in security.c
> > 
> > If we think that this is good enough, we proceed with the move of IMA
> > and EVM functions to the LSM infrastructure (patches v7 19-21).
> > 
> > The next patches are going to be similar to patches v6 22-23, but
> > unlike those, their goal would be simply to split metadata, not to make
> > IMA and EVM independent, which at this point has been addressed
> > separately in the prerequisite patches.
> > 
> > The final patch is to remove the 'integrity' LSM and the integrity
> > metadata management code, which now is not used anymore.
> > 
> > Would that work?
> 
> We are not making much progress, I'm going to follow any recommendation
> that would move this forward.