Received-SPF: pass (google.com: domain of linux-nfs+bounces-1906-linux.lists.archive=gmail.com@vger.kernel.org designates 2604:1380:4601:e00::3 as permitted sender) client-ip=2604:1380:4601:e00::3;
Message-ID: <b95967cd1aa2a4e751a8be3d23f72b7e1db0e4b6.camel@huaweicloud.com>
Subject: Re: [PATCH v9 19/25] integrity: Move
 integrity_kernel_module_request() to IMA
From: Roberto Sassu <roberto.sassu@huaweicloud.com>
To: Stefan Berger <stefanb@linux.ibm.com>, Paul Moore <paul@paul-moore.com>
Cc: viro@zeniv.linux.org.uk, brauner@kernel.org, chuck.lever@oracle.com, 
	jlayton@kernel.org, neilb@suse.de, kolga@netapp.com, Dai.Ngo@oracle.com, 
	tom@talpey.com, jmorris@namei.org, serge@hallyn.com, zohar@linux.ibm.com, 
	dmitry.kasatkin@gmail.com, eric.snowberg@oracle.com, dhowells@redhat.com, 
	jarkko@kernel.org, stephen.smalley.work@gmail.com, eparis@parisplace.org, 
	casey@schaufler-ca.com, shuah@kernel.org, mic@digikod.net, 
	linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org, 
	linux-nfs@vger.kernel.org, linux-security-module@vger.kernel.org, 
	linux-integrity@vger.kernel.org, keyrings@vger.kernel.org, 
	selinux@vger.kernel.org, linux-kselftest@vger.kernel.org, Roberto Sassu
	 <roberto.sassu@huawei.com>
Date: Tue, 13 Feb 2024 09:57:03 +0100
In-Reply-To: <7940b9d0-3133-4b08-b397-ad9ee34e3b34@linux.ibm.com>
References: <20240115181809.885385-1-roberto.sassu@huaweicloud.com>
	 <20240115181809.885385-20-roberto.sassu@huaweicloud.com>
	 <fd6ddc3d-e5d3-4b9c-b00b-ac2b1f22d653@linux.ibm.com>
	 <CAHC9VhTY=X7z5SRQZzFe25FGB2E3FBBkuZ_YYA1+ETyr7pv=tA@mail.gmail.com>
	 <7940b9d0-3133-4b08-b397-ad9ee34e3b34@linux.ibm.com>
Content-Type: text/plain; charset="UTF-8"
Content-Transfer-Encoding: quoted-printable
User-Agent: Evolution 3.44.4-0ubuntu2 
Precedence: bulk
MIME-Version: 1.0

On Mon, 2024-02-12 at 15:28 -0500, Stefan Berger wrote:
>=20
> On 2/12/24 12:56, Paul Moore wrote:
> > On Mon, Feb 12, 2024 at 12:48=E2=80=AFPM Stefan Berger <stefanb@linux.i=
bm.com> wrote:
> > > On 1/15/24 13:18, Roberto Sassu wrote:
> >=20
> > ...
> >=20
> > > > +/**
> > > > + * ima_kernel_module_request - Prevent crypto-pkcs1pad(rsa,*) requ=
ests
> > > > + * @kmod_name: kernel module name
> > > > + *
> > > > + * We have situation, when public_key_verify_signature() in case o=
f RSA > + * algorithm use alg_name to store internal information in order t=
o
> > > > + * construct an algorithm on the fly, but crypto_larval_lookup() w=
ill try
> > > > + * to use alg_name in order to load kernel module with same name.
> > > > + * Since we don't have any real "crypto-pkcs1pad(rsa,*)" kernel mo=
dules,
> > > > + * we are safe to fail such module request from crypto_larval_look=
up().
> > > > + *
> > > > + * In this way we prevent modprobe execution during digsig verific=
ation
> > > > + * and avoid possible deadlock if modprobe and/or it's dependencie=
s
> > > > + * also signed with digsig.
> > >=20
> > > This text needs to some reformulation at some point..
> >=20
> > There is no time like the present.  If you have a suggestion I would
> > love to hear it and I'm sure Roberto would too.
> >=20
>=20
> My interpretation of the issue after possibly lossy decoding of the=20
> above sentences:
>=20
> Avoid a deadlock by rejecting a virtual kernel module with the name=20
> "crypto-pkcs1pad(rsa,*)". This module may be requested by=20
> crypto_larval_lookup() while trying to verify an RSA signature in=20
> public_key_verify_signature(). Since the loading of the RSA module may=
=20
> itself cause the request for an RSA signature verification it will=20
> otherwise lead to a deadlock.

I can be even more precise I guess (I actually reproduced it).

Avoid a verification loop where verifying the signature of the modprobe
binary requires executing modprobe itself. Since the modprobe iint-
>mutex is already held when the signature verification is performed, a
deadlock occurs as soon as modprobe is executed within the critical
region, since the same lock cannot be taken again.

This happens when public_key_verify_signature(), in case of RSA
algorithm, use alg_name to store internal information in order to
construct an algorithm on the fly, but crypto_larval_lookup() will try
to use alg_name in order to load a kernel module with same name.

Since we don't have any real "crypto-pkcs1pad(rsa,*)" kernel modules,
we are safe to fail such module request from crypto_larval_lookup(),
and avoid the verification loop.

Roberto