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From: Ahmad Fatoum <a.fatoum@pengutronix.de>
To: Jarkko Sakkinen <jarkko@kernel.org>
Cc: Sumit Garg <sumit.garg@linaro.org>,
	David Howells <dhowells@redhat.com>,
	"Theodore Y. Ts'o" <tytso@mit.edu>,
	linux-security-module@vger.kernel.org,
	James Bottomley <jejb@linux.ibm.com>,
	James Morris <jmorris@namei.org>,
	Mimi Zohar <zohar@linux.ibm.com>,
	linux-kernel@vger.kernel.org, Eric Biggers <ebiggers@kernel.org>,
	linux-fscrypt@vger.kernel.org, keyrings@vger.kernel.org,
	linux-crypto@vger.kernel.org, kernel@pengutronix.de,
	Jaegeuk Kim <jaegeuk@kernel.org>,
	linux-integrity@vger.kernel.org,
	"Serge E. Hallyn" <serge@hallyn.com>
Subject: Re: [PATCH v2] fscrypt: support trusted keys
Date: Mon, 9 Aug 2021 12:02:45 +0200	[thread overview]
Message-ID: <57619a74-8292-64c6-0dbb-2f01de281652@pengutronix.de> (raw)
In-Reply-To: <10dac5c6-4530-217c-e1ea-a7e2e3572f43@pengutronix.de>

On 09.08.21 12:00, Ahmad Fatoum wrote:
> Hello Jarkko,
> 
> On 09.08.21 11:44, Jarkko Sakkinen wrote:
>> On Fri, Aug 06, 2021 at 05:09:28PM +0200, Ahmad Fatoum wrote:
>>> Kernel trusted keys don't require userspace knowledge of the raw key
>>> material and instead export a sealed blob, which can be persisted to
>>> unencrypted storage. Userspace can then load this blob into the kernel,
>>> where it's unsealed and from there on usable for kernel crypto.
>>>
>>> This is incompatible with fscrypt, where userspace is supposed to supply
>>> the raw key material. For TPMs, a work around is to do key unsealing in
>>> userspace, but this may not be feasible for other trusted key backends.
>>>
>>> Make it possible to benefit from both fscrypt and trusted key sealing
>>> by extending fscrypt_add_key_arg::key_id to hold either the ID of a
>>> fscrypt-provisioning or a trusted key.
>>>
>>> A non fscrypt-provisioning key_id was so far prohibited, so additionally
>>> allowing trusted keys won't break backwards compatibility.
>>>
>>> Signed-off-by: Ahmad Fatoum <a.fatoum@pengutronix.de>
>>> ---
>>> Tested with:
>>> https://github.com/google/fscryptctl/pull/23
>>> -	if (key->type != &key_type_fscrypt_provisioning)
>>> -		goto bad_key;
>>> -	payload = key->payload.data[0];
>>> +	if (key->type == &key_type_fscrypt_provisioning) {
>>
>> Why does fscrypt have own key type, and does not extend 'encrypted' with a
>> new format [*]?
> 
> See the commit[1] adding it for more information. TL;DR:
> 
> fscrypt maintainers would've preferred keys to be associated with
> a "domain". So an encrypted key generated for fscrypt use couldn't be reused
> for e.g. dm-crypt. They are wary of fscrypt users being more exposed if their
> keys can be used with weaker ciphers via other kernel functionality that could
> be used to extract information about the raw key material.
> 
> Eric also mentioned dislike of the possibility of rooting encrypted keys to
> user keys. v2 is only restricted to v2, so we didn't discuss this further.

Typo: v2 (of my series) is only restricted to s/v2/trusted keys/

> 
> Restricting the key to fscrypt-only precludes this reuse.
> 
> My commit makes no attempts in changing that. It just adds a new way to pass
> raw key material into fscrypt. For more information, see the commit[1] adding
> that key type.
> 
>> [*] https://www.kernel.org/doc/html/v5.13/security/keys/trusted-encrypted.html
> 
> [1]: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=93edd392ca
> 
> Cheers,
> Ahmad
> 


-- 
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  reply	other threads:[~2021-08-09 10:02 UTC|newest]

Thread overview: 23+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-08-06 15:09 Ahmad Fatoum
2021-08-09  9:44 ` Jarkko Sakkinen
2021-08-09 10:00   ` Ahmad Fatoum
2021-08-09 10:02     ` Ahmad Fatoum [this message]
2021-08-10 18:02     ` Jarkko Sakkinen
2021-08-09 20:52   ` Eric Biggers
2021-08-10 18:06     ` Jarkko Sakkinen
2021-08-10 18:46       ` Eric Biggers
2021-08-10 21:21         ` Jarkko Sakkinen
2021-08-10 21:27           ` Eric Biggers
2021-08-11  0:17             ` Jarkko Sakkinen
2021-08-11 11:34               ` Mimi Zohar
2021-08-11 17:16                 ` Eric Biggers
2021-08-12  0:54                   ` Mimi Zohar
2021-08-17 13:04                     ` Ahmad Fatoum
2021-08-17 13:55                       ` Mimi Zohar
2021-08-17 14:13                         ` Ahmad Fatoum
2021-08-17 14:24                           ` Mimi Zohar
2021-08-18  2:09                             ` Jarkko Sakkinen
2021-08-18  4:53                             ` Sumit Garg
2021-08-09 21:24 ` Eric Biggers
2021-08-10  7:41   ` Ahmad Fatoum
2021-08-10 17:35     ` Eric Biggers

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