From: James Morris <jmorris@namei.org>
To: Eric Biggers <ebiggers@kernel.org>
Cc: Jaskaran Khurana <jaskarankhurana@linux.microsoft.com>,
linux-security-module@vger.kernel.org,
linux-kernel@vger.kernel.org, linux-integrity@vger.kernel.org,
linux-fsdevel@vger.kernel.org, agk@redhat.com,
snitzer@redhat.com, dm-devel@redhat.com, scottsh@microsoft.com,
mpatocka@redhat.com, gmazyland@gmail.com
Subject: Re: [RFC PATCH v5 0/1] Add dm verity root hash pkcs7 sig validation.
Date: Fri, 28 Jun 2019 21:01:25 -0700 (PDT) [thread overview]
Message-ID: <alpine.LRH.2.21.1906282040490.15624@namei.org> (raw)
In-Reply-To: <20190628040041.GB673@sol.localdomain>
On Thu, 27 Jun 2019, Eric Biggers wrote:
> I don't understand your justification for this feature.
>
> If userspace has already been pwned severely enough for the attacker to be
> executing arbitrary code with CAP_SYS_ADMIN (which is what the device mapper
> ioctls need), what good are restrictions on loading more binaries from disk?
>
> Please explain your security model.
Let's say the system has a policy where all code must be signed with a
valid key, and that one mechanism for enforcing this is via signed
dm-verity volumes. Validating the signature within the kernel provides
stronger assurance than userspace validation. The kernel validates and
executes the code, using kernel-resident keys, and does not need to rely
on validation which has occurred across a trust boundary.
You don't need arbitrary CAP_SYS_ADMIN code execution, you just need a
flaw in the app (or its dependent libraries, or configuration) which
allows signature validation to be bypassed.
The attacker now needs a kernel rather than a userspace vulnerability to
bypass the signed code policy.
--
James Morris
<jmorris@namei.org>
next prev parent reply other threads:[~2019-06-29 4:01 UTC|newest]
Thread overview: 19+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-06-19 19:10 [RFC PATCH v5 0/1] Add dm verity root hash pkcs7 sig validation Jaskaran Khurana
2019-06-19 19:10 ` [RFC PATCH v5 1/1] " Jaskaran Khurana
2019-06-25 18:20 ` Mike Snitzer
2019-06-26 5:48 ` Milan Broz
2019-08-13 18:49 ` Jaskaran Singh Khurana
2019-06-27 12:17 ` Milan Broz
2019-06-28 1:52 ` Jaskaran Singh Khurana
2019-06-27 23:41 ` Eric Biggers
2019-06-28 1:49 ` Jaskaran Singh Khurana
2019-06-28 3:00 ` Eric Biggers
2019-06-28 5:12 ` Milan Broz
2019-06-28 17:03 ` Jaskaran Singh Khurana
2019-06-28 4:00 ` [RFC PATCH v5 0/1] " Eric Biggers
2019-06-28 19:45 ` Jaskaran Singh Khurana
2019-06-28 20:34 ` Eric Biggers
2019-06-28 23:27 ` Jaskaran Singh Khurana
2019-06-29 4:01 ` James Morris [this message]
2019-07-01 9:41 ` Milan Broz
2019-07-01 17:33 ` Jaskaran Singh Khurana
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