linux-kernel - Re: [PATCH v4] KEYS: encrypted: fix key instantiation with user-provided data

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Message-ID: <c0562c3-aa31-098-4473-ac8818fdc5a@vosn.de>
Date:   Sun, 23 Oct 2022 09:52:20 +0200 (CEST)
From:   Nikolaus Voss <nv@...n.de>
To:     Jarkko Sakkinen <jarkko@...nel.org>
cc:     Mimi Zohar <zohar@...ux.ibm.com>,
        David Howells <dhowells@...hat.com>,
        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>,
        linux-integrity@...r.kernel.org, keyrings@...r.kernel.org,
        linux-security-module@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v4] KEYS: encrypted: fix key instantiation with user-provided
 data

On Sun, 23 Oct 2022, Jarkko Sakkinen wrote:
> On Sun, Oct 23, 2022 at 08:18:58AM +0300, Jarkko Sakkinen wrote:
>> On Thu, Oct 13, 2022 at 08:39:58AM +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
>>>
>>> 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.
>>>
>>> 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/
>>> Signed-off-by: Nikolaus Voss <nikolaus.voss@...g-streit.com>
>>> ---
>>> Changes
>>> =======
>>> v4: - fixed link
>>> v3: - use generated random key in example, reformat commit message
>>> 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
>>>
>>>  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..9bc9db8ec651 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=$(dd if=/dev/urandom bs=1 count=32 | xxd -c32 -p)
>>> +    $ keyctl add encrypted evm "new default user:kmk 32 $evmkey" @u
>>>      794890253
>>>
>>>      $ keyctl print 794890253
>>> diff --git a/security/keys/encrypted-keys/encrypted.c b/security/keys/encrypted-keys/encrypted.c
>>> index e05cfc2e49ae..1e313982af02 100644
>>> --- a/security/keys/encrypted-keys/encrypted.c
>>> +++ b/security/keys/encrypted-keys/encrypted.c
>>> @@ -627,7 +627,7 @@ static struct encrypted_key_payload *encrypted_key_alloc(struct key *key,
>>>  			pr_err("encrypted key: instantiation of keys using provided decrypted data is disabled since CONFIG_USER_DECRYPTED_DATA is set to false\n");
>>>  			return ERR_PTR(-EINVAL);
>>>  		}
>>> -		if (strlen(decrypted_data) != decrypted_datalen) {
>>> +		if (strlen(decrypted_data) != decrypted_datalen * 2) {
>>>  			pr_err("encrypted key: decrypted data provided does not match decrypted data length provided\n");
>>>  			return ERR_PTR(-EINVAL);
>>>  		}
>>> @@ -791,8 +791,8 @@ static int encrypted_init(struct encrypted_key_payload *epayload,
>>>  		ret = encrypted_key_decrypt(epayload, format, hex_encoded_iv);
>>>  	} else if (decrypted_data) {
>>>  		get_random_bytes(epayload->iv, ivsize);
>>> -		memcpy(epayload->decrypted_data, decrypted_data,
>>> -				   epayload->decrypted_datalen);
>>> +		ret = hex2bin(epayload->decrypted_data, decrypted_data,
>>> +			      epayload->decrypted_datalen);
>>>  	} else {
>>>  		get_random_bytes(epayload->iv, ivsize);
>>>  		get_random_bytes(epayload->decrypted_data, epayload->decrypted_datalen);
>>> --
>>> 2.34.1
>>>
>>
>>
>> Reviewed-by: Jarkko Sakkinen <jarkko@...nel.org>
>>
>> Unless there is opposing views, I can pick this.
>
> Actually, taking this back: please fix the checkpatch warnings first.

I fixed the warnings in v5, Mimi took this already.

Niko