linux-kernel - Re: [PATCH v5] KEYS: encrypted: fix key instantiation with user-provided data

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Date:   Wed, 19 Oct 2022 12:31:47 -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 v5] KEYS: encrypted: fix key instantiation with
 user-provided data

Hi Nikolaus,

On Wed, 2022-10-19 at 16:07 +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.
> 
> Old 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 $BROKENKEY | xxd -p -c32)
> keyctl add user masterkey "$(cat masterkey.bin)" @u
> keyctl add encrypted testkey "new user:masterkey 32 $NEWKEY" @u
> 
> However, NEWKEY is still broken: If for BROKENKEY 32 bytes were specified, a
> brute force attacker knowing the key properties would only need to try at most
> 2^(16*8) keys, as if the key was only 16 bytes long.
> 
> The security issue is a result of the combination of limiting the input range
> to hex-ascii and using memcpy() instead of hex2bin(). It could have been fixed
> either by allowing binary input or using hex2bin() (and doubling the ascii
> input key length). This patch implements the latter.
> 
> The corresponding test for the Linux Test Project ltp has also been
> fixed (see link below).
> 
> Fixes: cd3bc044af48 ("KEYS: encrypted: Instantiate key with user-provided decrypted data")
> Cc: stable <stable@...nel.org>
> Link: https://lore.kernel.org/ltp/20221006081709.92303897@mail.steuer-voss.de/
> Reviewed-by: Mimi Zohar <zohar@...ux.ibm.com>
> Signed-off-by: Nikolaus Voss <nikolaus.voss@...g-streit.com>

While preparing to queue this patch, I noticed scripts/checkpatch.pl
returns a couple of warnings, including that the sender email address
and your tag here don't match.  Wish I had caught them earlier.
-- 
thanks,

Mimi