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Subject: Re: [PATCH v5 23/23] integrity: Switch from rbtree to LSM-managed
 blob for integrity_iint_cache
From: Roberto Sassu <roberto.sassu@huaweicloud.com>
To: Mimi Zohar <zohar@linux.ibm.com>, Paul Moore <paul@paul-moore.com>
Cc: viro@zeniv.linux.org.uk, brauner@kernel.org, chuck.lever@oracle.com, 
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 keyrings@vger.kernel.org,  selinux@vger.kernel.org, Roberto Sassu
 <roberto.sassu@huawei.com>
Date: Wed, 06 Dec 2023 17:50:16 +0100
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On Wed, 2023-12-06 at 11:11 -0500, Mimi Zohar wrote:
> On Wed, 2023-12-06 at 14:10 +0100, Roberto Sassu wrote:
> > On Mon, 2023-12-04 at 14:26 +0100, Roberto Sassu wrote:
>=20
> ...
> > > 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.
> > >=20
> > > These are the changes I have in mind:
> > >=20
> > > 1) Fix evm_verifyxattr(), and make it work without integrity_iint_cac=
he
> > > 2) Remove the integrity_iint_cache parameter from evm_verifyxattr(),
> > >    since the other callers are not going to use it
> >=20
> > Ehm, I checked better.
> >=20
> > integrity_inode_get() is public too (although it is not exported). So,
> > a caller (not IMA) could do:
> >=20
> > iint =3D integrity_inode_get(inode);
> > status =3D evm_verifyxattr(..., iint);
> >=20
> > 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).

Oh, I needed to add a check for the iint here:


void integrity_inode_free(struct inode *inode)
{
	struct integrity_iint_cache *iint;

	if (!IS_IMA(inode))
		return;

	iint =3D integrity_iint_find(inode);
	if (!iint)                          <=3D=3D=3D this
		return;

	integrity_inode_set_iint(inode, NULL);

	iint_free(iint);
}

> Calling integrity_inode_free() directly would release the iint early. =
=20
> As a result, IMA would then need to re-allocate it on next access.=20
> Other than impacting IMA's performance, is this a problem?

Uhm, I think the iint could be freed while IMA is using it, for example
in process_measurement().

Roberto

> > > 3) Create an internal function with the original parameters to be use=
d
> > >    by IMA
> > > 4) Introduce evm_post_path_mknod(), which similarly to
> > >    ima_post_path_mknod(), sets IMA_NEW_FILE for new files
> >=20
> > I just realized that also this is changing the current behavior.
> >=20
> > 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).
>=20
> True
>=20
> Mimi
>=20
> > > 5) Add hardcoded call to evm_post_path_mknod() after
> > >    ima_post_path_mknod() in security.c
> > >=20
> > > 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).
> > >=20
> > > 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 ma=
ke
> > > IMA and EVM independent, which at this point has been addressed
> > > separately in the prerequisite patches.
> > >=20
> > > The final patch is to remove the 'integrity' LSM and the integrity
> > > metadata management code, which now is not used anymore.
> > >=20
> > > Would that work?
> >=20
> > We are not making much progress, I'm going to follow any recommendation
> > that would move this forward.
>=20