Re: [PATCH v7 3/6] security: keys: trusted: fix TPM2 authorizations

[Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com>]

On Wed, Mar 04, 2020 at 06:27:41PM -0800, James Bottomley wrote:
> In TPM 1.2 an authorization was a 20 byte number.  The spec actually
> recommended you to hash variable length passwords and use the sha1
> hash as the authorization.  Because the spec doesn't require this
> hashing, the current authorization for trusted keys is a 40 digit hex
> number.  For TPM 2.0 the spec allows the passing in of variable length
> passwords and passphrases directly, so we should allow that in trusted
> keys for ease of use.  Update the 'blobauth' parameter to take this
> into account, so we can now use plain text passwords for the keys.
> 
> so before
> 
> keyctl add trusted kmk "new 32 blobauthõ72d396fae9206628714fb2ce00f72e94f2258f"
> 
> after we will accept both the old hex sha1 form as well as a new
> directly supplied password:
> 
> keyctl add trusted kmk "new 32 blobauth=hello keyhandle000001"
> 
> Since a sha1 hex code must be exactly 40 bytes long and a direct
> password must be 20 or less, we use the length as the discriminator
> for which form is input.
> 
> Note this is both and enhancement and a potential bug fix.  The TPM
> 2.0 spec requires us to strip leading zeros, meaning empyty
> authorization is a zero length HMAC whereas we're currently passing in
> 20 bytes of zeros.  A lot of TPMs simply accept this as OK, but the
> Microsoft TPM emulator rejects it with TPM_RC_BAD_AUTH, so this patch
> makes the Microsoft TPM emulator work with trusted keys.
> 
> Fixes: 0fe5480303a1 ("keys, trusted: seal/unseal with TPM 2.0 chips")
> Signed-off-by: James Bottomley <James.Bottomley@HansenPartnership.com>

Reviewed-by: Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com>

/Jarkko