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[68.61.232.219]) by smtp.gmail.com with ESMTPSA id p13sm2089843ilb.61.2020.08.13.07.56.18 (version=TLS1_2 cipher=ECDHE-ECDSA-AES128-GCM-SHA256 bits=128/128); Thu, 13 Aug 2020 07:56:19 -0700 (PDT) Content-Type: text/plain; charset=us-ascii Mime-Version: 1.0 (Mac OS X Mail 13.4 \(3608.80.23.2.2\)) Subject: Re: [dm-devel] [RFC PATCH v5 00/11] Integrity Policy Enforcement LSM (IPE) From: Chuck Lever In-Reply-To: <1597329763.3708.13.camel@HansenPartnership.com> Date: Thu, 13 Aug 2020 10:56:17 -0400 Cc: Mimi Zohar , James Morris , Deven Bowers , Pavel Machek , Sasha Levin , snitzer@redhat.com, dm-devel@redhat.com, tyhicks@linux.microsoft.com, agk@redhat.com, Paul Moore , Jonathan Corbet , nramas@linux.microsoft.com, serge@hallyn.com, pasha.tatashin@soleen.com, Jann Horn , linux-block@vger.kernel.org, Al Viro , Jens Axboe , mdsakib@microsoft.com, open list , eparis@redhat.com, linux-security-module@vger.kernel.org, linux-audit@redhat.com, linux-fsdevel , linux-integrity@vger.kernel.org, jaskarankhurana@linux.microsoft.com Content-Transfer-Encoding: quoted-printable Message-Id: <49A45475-20D8-456E-92AD-F63DBC71F900@gmail.com> References: <20200728213614.586312-1-deven.desai@linux.microsoft.com> <20200802115545.GA1162@bug> <20200802140300.GA2975990@sasha-vm> <20200802143143.GB20261@amd> <1596386606.4087.20.camel@HansenPartnership.com> <1596639689.3457.17.camel@HansenPartnership.com> <329E8DBA-049E-4959-AFD4-9D118DEB176E@gmail.com> <1597073737.3966.12.camel@HansenPartnership.com> <6E907A22-02CC-42DD-B3CD-11D304F3A1A8@gmail.com> <1597124623.30793.14.camel@HansenPartnership.com> <16C3BF97-A7D3-488A-9D26-7C9B18AD2084@gmail.com> <1597170509.4325.55.camel@HansenPartnership.com> <2CA41152-6445-4716-B5EE-2D14E5C59368@gmail.com> <1597246946.7293.9.camel@HansenPartnership.com> <3F328A12-25DD-418B-A7D0-64DA09236E1C@gmail.com> <1597329763.3708.13.camel@HansenPartnership.com> To: James Bottomley X-Mailer: Apple Mail (2.3608.80.23.2.2) Sender: linux-integrity-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-integrity@vger.kernel.org > On Aug 13, 2020, at 10:42 AM, James Bottomley = wrote: >=20 > On Thu, 2020-08-13 at 10:21 -0400, Chuck Lever wrote: >>> On Aug 12, 2020, at 11:42 AM, James Bottomley >> enPartnership.com> wrote: > [...] >>> For most people the security mechanism of local xattrs is >>> sufficient. If you're paranoid, you don't believe it is and you >>> use EVM. >>=20 >> When IMA metadata happens to be stored in local filesystems in >> a trusted xattr, it's going to enjoy the protection you describe >> without needing the addition of a cryptographic signature. >>=20 >> However, that metadata doesn't live its whole life there. It >> can reside in a tar file, it can cross a network, it can live >> on a back-up tape. I think we agree that any time that metadata >> is in transit or at rest outside of a Linux local filesystem, it >> is exposed. >>=20 >> Thus I'm interested in a metadata protection mechanism that does >> not rely on the security characteristics of a particular storage >> container. For me, a cryptographic signature fits that bill >> nicely. >=20 > Sure, but one of the points about IMA is a separation of mechanism = from > policy. Signed hashes (called appraisal in IMA terms) is just one > policy you can decide to require or not or even make it conditional on > other things. AFAICT, the current EVM_IMA_DIGSIG and EVM_PORTABLE_DIGSIG formats are always signed. The policy choice is whether or not to verify the signature, not whether or not the metadata format is signed. -- Chuck Lever chucklever@gmail.com