linux-kernel - Re: [RFC PATCH v1] fscrypt: support encrypted and trusted keys

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Date:   Thu, 29 Jul 2021 01:22:43 +0300
From:   Jarkko Sakkinen <jarkko@...nel.org>
To:     Ahmad Fatoum <a.fatoum@...gutronix.de>
Cc:     "Theodore Y. Ts'o" <tytso@....edu>,
        Jaegeuk Kim <jaegeuk@...nel.org>,
        Eric Biggers <ebiggers@...nel.org>,
        James Morris <jmorris@...ei.org>,
        "Serge E. Hallyn" <serge@...lyn.com>,
        James Bottomley <jejb@...ux.ibm.com>,
        Mimi Zohar <zohar@...ux.ibm.com>,
        Sumit Garg <sumit.garg@...aro.org>,
        David Howells <dhowells@...hat.com>,
        linux-fscrypt@...r.kernel.org, linux-crypto@...r.kernel.org,
        linux-integrity@...r.kernel.org,
        linux-security-module@...r.kernel.org, keyrings@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH v1] fscrypt: support encrypted and trusted keys

On Tue, Jul 27, 2021 at 04:43:49PM +0200, Ahmad Fatoum wrote:
> For both v1 and v2 key setup mechanisms, userspace supplies the raw key
> material to the kernel after which it is never again disclosed to
> userspace.
> 
> Use of encrypted and trusted keys offers stronger guarantees:
> The key material is generated within the kernel and is never disclosed to
> userspace in clear text and, in the case of trusted keys, can be
> directly rooted to a trust source like a TPM chip.
> 
> Add support for trusted and encrypted keys by repurposing
> fscrypt_add_key_arg::raw to hold the key description when the new
> FSCRYPT_KEY_ARG_TYPE_DESC flag is supplied. The location of the flag
> was previously reserved and enforced by ioctl code to be zero, so this
> change won't break backwards compatibility.
> 
> Corresponding userspace patches are available for fscryptctl:
> https://github.com/google/fscryptctl/pull/23
> 
> Signed-off-by: Ahmad Fatoum <a.fatoum@...gutronix.de>
> ---
> key_extract_material used by this patch is added in
> <cover.b2fdd70b830d12853b12a12e32ceb0c8162c1346.1626945419.git-series.a.fatoum@...gutronix.de>
> which still awaits feedback.
> 
> Sending this RFC out anyway to get some feedback from the fscrypt
> developers whether this is the correct way to go about it.
> 
> To: "Theodore Y. Ts'o" <tytso@....edu>
> To: Jaegeuk Kim <jaegeuk@...nel.org>
> To: Eric Biggers <ebiggers@...nel.org>
> Cc: Jarkko Sakkinen <jarkko@...nel.org>
> Cc: James Morris <jmorris@...ei.org>
> Cc: "Serge E. Hallyn" <serge@...lyn.com>
> Cc: James Bottomley <jejb@...ux.ibm.com>
> Cc: Mimi Zohar <zohar@...ux.ibm.com>
> Cc: Sumit Garg <sumit.garg@...aro.org>
> Cc: David Howells <dhowells@...hat.com>
> Cc: linux-fscrypt@...r.kernel.org
> Cc: linux-crypto@...r.kernel.org
> Cc: linux-integrity@...r.kernel.org
> Cc: linux-security-module@...r.kernel.org
> Cc: keyrings@...r.kernel.org
> Cc: linux-kernel@...r.kernel.org
> ---
>  Documentation/filesystems/fscrypt.rst | 24 ++++++++---
>  fs/crypto/keyring.c                   | 59 ++++++++++++++++++++++++---
>  include/uapi/linux/fscrypt.h          | 16 +++++++-
>  3 files changed, 87 insertions(+), 12 deletions(-)
> 
> diff --git a/Documentation/filesystems/fscrypt.rst b/Documentation/filesystems/fscrypt.rst
> index 44b67ebd6e40..83738af2afa3 100644
> --- a/Documentation/filesystems/fscrypt.rst
> +++ b/Documentation/filesystems/fscrypt.rst
> @@ -681,11 +681,15 @@ It can be executed on any file or directory on the target filesystem,
>  but using the filesystem's root directory is recommended.  It takes in
>  a pointer to struct fscrypt_add_key_arg, defined as follows::
>  
> +    #define FSCRYPT_KEY_ADD_RAW_ASIS		0
> +    #define FSCRYPT_KEY_ADD_RAW_DESC		1

Would be nice to have these documented.

/Jarkko