Re: [PATCH v13 3/5] security: keys: trusted: fix TPM2 authorizations

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

On Mon, Sep 21, 2020 at 07:28:07PM -0700, 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 blobauthõ72d396fae9206628714fb2ce00f72e94f2258fkeyhandle000001" @u
> 
> 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" @u
> 
> 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>
> 
> ---
> 
> v6: change comment, eliminate else clauses and add fixes tag
> v7: fixes before signoff
> v12: fix mismerge from v6 to make processing continue after blobauth
> 
> Merge with auth fix
> ---
>  include/keys/trusted-type.h               |  1 +
>  security/keys/trusted-keys/trusted_tpm1.c | 32 ++++++++++++++++++-----
>  security/keys/trusted-keys/trusted_tpm2.c | 10 ++++---
>  3 files changed, 33 insertions(+), 10 deletions(-)
> 
> diff --git a/include/keys/trusted-type.h b/include/keys/trusted-type.h
> index a94c03a61d8f..b2ed3481c6a0 100644
> --- a/include/keys/trusted-type.h
> +++ b/include/keys/trusted-type.h
> @@ -30,6 +30,7 @@ struct trusted_key_options {
>  	uint16_t keytype;
>  	uint32_t keyhandle;
>  	unsigned char keyauth[TPM_DIGEST_SIZE];
> +	uint32_t blobauth_len;
>  	unsigned char blobauth[TPM_DIGEST_SIZE];
>  	uint32_t pcrinfo_len;
>  	unsigned char pcrinfo[MAX_PCRINFO_SIZE];
> diff --git a/security/keys/trusted-keys/trusted_tpm1.c b/security/keys/trusted-keys/trusted_tpm1.c
> index b9fe02e5f84f..eaa2e7ca136e 100644
> --- a/security/keys/trusted-keys/trusted_tpm1.c
> +++ b/security/keys/trusted-keys/trusted_tpm1.c
> @@ -781,13 +781,33 @@ static int getoptions(char *c, struct trusted_key_payload *pay,
>  				return -EINVAL;
>  			break;
>  		case Opt_blobauth:
> -			if (strlen(args[0].from) != 2 * SHA1_DIGEST_SIZE)
> -				return -EINVAL;
> -			res = hex2bin(opt->blobauth, args[0].from,
> -				      SHA1_DIGEST_SIZE);
> -			if (res < 0)
> -				return -EINVAL;
> +			/*
> +			 * TPM 1.2 authorizations are sha1 hashes passed in as
> +			 * hex strings.  TPM 2.0 authorizations are simple
> +			 * passwords (although it can take a hash as well)
> +			 */
> +			opt->blobauth_len = strlen(args[0].from);
> +
> +			if (opt->blobauth_len = 2 * TPM_DIGEST_SIZE) {
> +				res = hex2bin(opt->blobauth, args[0].from,
> +					      TPM_DIGEST_SIZE);
> +				if (res < 0)
> +					return -EINVAL;
> +
> +				opt->blobauth_len = TPM_DIGEST_SIZE;
> +				break;
> +			}
> +
> +			if (tpm2 && opt->blobauth_len <= sizeof(opt->blobauth)) {
> +				memcpy(opt->blobauth, args[0].from,
> +				       opt->blobauth_len);
> +				break;
> +			}
> +
> +			return -EINVAL;
> +
>  			break;
> +
>  		case Opt_migratable:
>  			if (*args[0].from = '0')
>  				pay->migratable = 0;
> diff --git a/security/keys/trusted-keys/trusted_tpm2.c b/security/keys/trusted-keys/trusted_tpm2.c
> index 08ec7f48f01d..b4a5058107c2 100644
> --- a/security/keys/trusted-keys/trusted_tpm2.c
> +++ b/security/keys/trusted-keys/trusted_tpm2.c
> @@ -91,10 +91,12 @@ int tpm2_seal_trusted(struct tpm_chip *chip,
>  			     TPM_DIGEST_SIZE);
>  
>  	/* sensitive */
> -	tpm_buf_append_u16(&buf, 4 + TPM_DIGEST_SIZE + payload->key_len + 1);
> +	tpm_buf_append_u16(&buf, 4 + options->blobauth_len + payload->key_len + 1);
> +
> +	tpm_buf_append_u16(&buf, options->blobauth_len);
> +	if (options->blobauth_len)
> +		tpm_buf_append(&buf, options->blobauth, options->blobauth_len);
>  
> -	tpm_buf_append_u16(&buf, TPM_DIGEST_SIZE);
> -	tpm_buf_append(&buf, options->blobauth, TPM_DIGEST_SIZE);
>  	tpm_buf_append_u16(&buf, payload->key_len + 1);
>  	tpm_buf_append(&buf, payload->key, payload->key_len);
>  	tpm_buf_append_u8(&buf, payload->migratable);
> @@ -258,7 +260,7 @@ static int tpm2_unseal_cmd(struct tpm_chip *chip,
>  			     NULL /* nonce */, 0,
>  			     TPM2_SA_CONTINUE_SESSION,
>  			     options->blobauth /* hmac */,
> -			     TPM_DIGEST_SIZE);
> +			     options->blobauth_len);
>  
>  	rc = tpm_send(chip, buf.data, tpm_buf_length(&buf));
>  	if (rc > 0)
> -- 
> 2.26.2
> 

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

Transcript:

➜  tpm2-scripts (master) ✗ sudo ./tpm2-root-key
0x80000000
âžœ  tpm2-scripts (master) ✗ sudo keyctl add trusted kmk "new 32 blobauth=hello keyhandle€000000" @u
751240563

/Jarkko