linux-kernel - Re: [PATCH v6] KEYS: encrypted: fix key instantiation with user-provided data

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Message-ID: <075b53e67638b4da85da9299b59fe2662a765c92.camel@linux.ibm.com>
Date:   Wed, 19 Oct 2022 17:28:23 -0400
From:   Mimi Zohar <zohar@...ux.ibm.com>
To:     Nikolaus Voss <nikolaus.voss@...g-streit.com>,
        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 v6] KEYS: encrypted: fix key instantiation with
 user-provided data

On Wed, 2022-10-19 at 18:38 +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@...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>

Thanks!  This patch is now queued in next-integrity/next-integrity-
testing.

-- 
thanks,

Mimi