linux-kernel - Re: [PATCH v2] KEYS: encrypted: fix key instantiation with user-provided data

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Date:   Wed, 12 Oct 2022 22:47:17 -0400
From:   Mimi Zohar <zohar@...ux.ibm.com>
To:     Nikolaus Voss <nv@...n.de>, David Howells <dhowells@...hat.com>,
        Jarkko Sakkinen <jarkko@...nel.org>,
        James Morris <jmorris@...ei.org>,
        "Serge E. Hallyn" <serge@...lyn.com>, Yael Tzur <yaelt@...gle.com>,
        Cyril Hrubis <chrubis@...e.cz>, Petr Vorel <pvorel@...e.cz>
Cc:     linux-integrity@...r.kernel.org, keyrings@...r.kernel.org,
        linux-security-module@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] KEYS: encrypted: fix key instantiation with
 user-provided data

Hi Nikolaus,

On Wed, 2022-10-12 at 17:09 +0200, Nikolaus Voss wrote:
> Commit cd3bc044af48 ("KEYS: encrypted: Instantiate key with user-provided
> decrypted data") added key instantiation with user provided decrypted data.
> The user data is hex-ascii-encoded but was just memcpy'ed to the binary buffer.
> Fix this to use hex2bin instead.
> 
> Keys created from user provided decrypted data saved with "keyctl pipe"
> are still valid, however if the key is recreated from decrypted data the
> old key must be converted to the correct format. This can be done with a
> small shell script, e.g.:
> 
> BROKENKEY=abcdefABCDEF1234567890aaaaaaaaaa
> NEWKEY=$(echo -ne $BROKENKEY | xxd -p -c64)
> keyctl add user masterkey "$(cat masterkey.bin)" @u
> keyctl add encrypted testkey "new user:masterkey 32 $NEWKEY" @u
> 
> It is encouraged to switch to a new key because the effective key size
> of the old keys is only half of the specified size.

Thank you for updating the patch description.

> 
> The corresponding test for the Linux Test Project ltp has been fixed
> with this patch:
> https://lists.linux.it/pipermail/ltp/2022-October/031060.html

Perhaps make this a "Link:" line and move it before your "Signed-off-
by".
> 
> Changes
> =======

As per Documentation/process/submitting-patches.rst, the changelog
belongs after the "---" separator. 

> v2: - clarify commit message, add example to recover old/broken keys
>     - improve example in Documentation/security/keys/trusted-encrypted.rst
>     - add link to ltp patch
> 
> Fixes: cd3bc044af48 ("KEYS: encrypted: Instantiate key with user-provided decrypted data")
> Cc: stable <stable@...nel.org>
> Signed-off-by: Nikolaus Voss <nikolaus.voss@...g-streit.com>
> ---
>  Documentation/security/keys/trusted-encrypted.rst | 3 ++-
>  security/keys/encrypted-keys/encrypted.c          | 6 +++---
>  2 files changed, 5 insertions(+), 4 deletions(-)
> 
> diff --git a/Documentation/security/keys/trusted-encrypted.rst b/Documentation/security/keys/trusted-encrypted.rst
> index 0bfb4c339748..e81e47db0b4c 100644
> --- a/Documentation/security/keys/trusted-encrypted.rst
> +++ b/Documentation/security/keys/trusted-encrypted.rst
> @@ -350,7 +350,8 @@ Load an encrypted key "evm" from saved blob::
>  
>  Instantiate an encrypted key "evm" using user-provided decrypted data::
>  
> -    $ keyctl add encrypted evm "new default user:kmk 32 `cat evm_decrypted_data.blob`" @u
> +    $ evmkey=abcdefABCDEF1234567890aaaaaaaaaaabcdefABCDEF1234567890aaaaaaaaaa
> +    $ keyctl add encrypted evm "new default user:kmk 32 $evmkey" @u
>      794890253

As example code is often re-used, I would avoid including the key data
on the command line.

-- 
thanks,

Mimi