Re: [PATCH v3 25/25] integrity: Switch from rbtree to LSM-managed blob for integrity_iint_cache

Roberto Sassu
2023-10-13T11:32:46Z

On Fri, 2023-09-15 at 11:39 +0200, Roberto Sassu wrote:
> On Tue, 2023-09-12 at 12:19 -0400, Stefan Berger wrote:
> > On 9/4/23 09:40, Roberto Sassu wrote:
> > > From: Roberto Sassu <roberto.sassu@huawei.com>
> > >
> > > Before the security field of kernel objects could be shared among LSMs with
> > > the LSM stacking feature, IMA and EVM had to rely on an alternative storage
> > > of inode metadata. The association between inode metadata and inode is
> > > maintained through an rbtree.
> > >
> > > With the reservation mechanism offered by the LSM infrastructure, the
> > > rbtree is no longer necessary, as each LSM could reserve a space in the
> > > security blob for each inode. Thus, request from the 'integrity' LSM a
> > > space in the security blob for the pointer of inode metadata
> > > (integrity_iint_cache structure).
> > >
> > > Prefer this to allocating the integrity_iint_cache structure directly, as
> > > IMA would require it only for a subset of inodes. Always allocating it
> > > would cause a waste of memory.
> > >
> > > Introduce two primitives for getting and setting the pointer of
> > > integrity_iint_cache in the security blob, respectively
> > > integrity_inode_get_iint() and integrity_inode_set_iint(). This would make
> > > the code more understandable, as they directly replace rbtree operations.
> > >
> > > Locking is not needed, as access to inode metadata is not shared, it is per
> > > inode.
> > >
> > > Signed-off-by: Roberto Sassu <roberto.sassu@huawei.com>
> > > Reviewed-by: Casey Schaufler <casey@schaufler-ca.com>
> > > ---
> > >
> > > @@ -145,10 +91,8 @@ static void integrity_inode_free(struct inode *inode)
> > > if (!IS_IMA(inode))
> > > return;
> >
> > I think you can remove this check !IS_IMA()  as well since the next
> > function called here integrity_iint_find() already has this check:
> >
> > struct integrity_iint_cache *integrity_iint_find(struct inode *inode)
> > {
> >         if (!IS_IMA(inode))
> >                 return NULL;
> >
> >         return integrity_inode_get_iint(inode);
> > }
>
> I agree, thanks!

Actually, I had to keep it otherwise, without a check on iint,
iint_free() can get NULL as argument.

Roberto

> Roberto
>
> > >
> > > - write_lock(&integrity_iint_lock);
> > > - iint = __integrity_iint_find(inode);
> > > - rb_erase(&iint->rb_node, &integrity_iint_tree);
> > > - write_unlock(&integrity_iint_lock);
> > > + iint = integrity_iint_find(inode); <--------------
> > > + integrity_inode_set_iint(inode, NULL);
> > >
> > > iint_free(iint);
> > > }
>