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

[Jarkko Sakkinen]

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 at kernel.org>
> Link: https://lore.kernel.org/ltp/20221006081709.92303897@mail.steuer-voss.de/
> Signed-off-by: Nikolaus Voss <nikolaus.voss at haag-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 at kernel.org>

Unless there is opposing views, I can pick this.

BR, Jarkko