From: Jaskaran Singh Khurana <jaskarankhurana@linux.microsoft.com>
To: Milan Broz <gmazyland@gmail.com>
Cc: James Morris <jmorris@namei.org>,
Eric Biggers <ebiggers@kernel.org>,
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
Subject: Re: [RFC PATCH v5 0/1] Add dm verity root hash pkcs7 sig validation.
Date: Mon, 1 Jul 2019 10:33:00 -0700 (PDT) [thread overview]
Message-ID: <alpine.LRH.2.21.1907011029100.31396@linuxonhyperv3.guj3yctzbm1etfxqx2vob5hsef.xx.inter> (raw)
In-Reply-To: <749ddf56-3cb6-42c8-9ccc-71e09558400f@gmail.com>
Hello Milan,
On Mon, 1 Jul 2019, Milan Broz wrote:
> On 29/06/2019 06:01, James Morris wrote:
>> 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.
>
> Yes, but as it is implemented in this patch, a certificate is provided as
> a binary blob by the (super)user that activates the dm-verity device.
>
> Actually, I can put there anything that looks like a correct signature (self-signed
> or so), and dm-verity code is happy because the root hash is now signed.
>
> Maybe could this concept be extended to support in-kernel compiled certificates?
>
> I like the idea of signed root hash, but the truth is that if you have access
> to device activation, it brings nothing, you can just put any cert in the keyring
> and use it.
>
> Milan
>
The signature needs to be trusted by the .builtin_trusted_keys which is
a read-only list of keys that were compiled into the kernel. The
verify_pkcs7_signature verifies trust against the builtin keyring so I
think what you are suggesting is covered here.
Regards,
Jaskaran.
prev parent reply other threads:[~2019-07-01 17:33 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
2019-07-01 9:41 ` Milan Broz
2019-07-01 17:33 ` Jaskaran Singh Khurana [this message]
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