Re: [PATCH v5 8/8] KEYS: trusted: tpm2: Use struct tpm_buf for sized buffers

["Serge E. Hallyn" <serge@hallyn.com>]

On Wed, Nov 22, 2023 at 12:31:20AM +0200, Jarkko Sakkinen wrote:
> Take advantage of the new sized buffer (TPM2B) mode of struct tpm_buf in
> tpm2_seal_trusted(). This allows to add robustness to the command
> construction without requiring to calculate buffer sizes manually.
> 
> Signed-off-by: Jarkko Sakkinen <jarkko@kernel.org>
> ---
> v3 [2023-11-21]: A boundary error check as response for the feeedback
> from Mario Limenciello:
> https://lore.kernel.org/linux-integrity/3f9086f6-935f-48a7-889b-c71398422fa1@amd.com/
> v2: Use tpm_buf_read_*
> ---
>  security/keys/trusted-keys/trusted_tpm2.c | 54 +++++++++++++----------
>  1 file changed, 31 insertions(+), 23 deletions(-)
> 
> diff --git a/security/keys/trusted-keys/trusted_tpm2.c b/security/keys/trusted-keys/trusted_tpm2.c
> index bc700f85f80b..97b1dfca2dba 100644
> --- a/security/keys/trusted-keys/trusted_tpm2.c
> +++ b/security/keys/trusted-keys/trusted_tpm2.c
> @@ -228,8 +228,9 @@ int tpm2_seal_trusted(struct tpm_chip *chip,
>  		      struct trusted_key_payload *payload,
>  		      struct trusted_key_options *options)
>  {
> +	off_t offset = TPM_HEADER_SIZE;
> +	struct tpm_buf buf, sized;
>  	int blob_len = 0;
> -	struct tpm_buf buf;
>  	u32 hash;
>  	u32 flags;
>  	int i;
> @@ -258,6 +259,14 @@ int tpm2_seal_trusted(struct tpm_chip *chip,
>  		return rc;
>  	}
>  
> +	rc = tpm_buf_init_sized(&sized);
> +	if (rc) {
> +		tpm_buf_destroy(&buf);

It won't really hurt, but at the moment if tpm_buf_init_sized() returns
non-zero, then it must be returning -ENOMEM, and tpm_buf_destroy(&buf)
is not needed, right?

> +		tpm_put_ops(chip);
> +		return rc;
> +	}
> +
> +	tpm_buf_reset(&buf, TPM2_ST_SESSIONS, TPM2_CC_CREATE);
>  	tpm_buf_append_u32(&buf, options->keyhandle);
>  	tpm2_buf_append_auth(&buf, TPM2_RS_PW,
>  			     NULL /* nonce */, 0,
> @@ -266,36 +275,36 @@ int tpm2_seal_trusted(struct tpm_chip *chip,
>  			     TPM_DIGEST_SIZE);
>  
>  	/* sensitive */
> -	tpm_buf_append_u16(&buf, 4 + options->blobauth_len + payload->key_len);
> +	tpm_buf_append_u16(&sized, options->blobauth_len);
>  
> -	tpm_buf_append_u16(&buf, options->blobauth_len);
>  	if (options->blobauth_len)
> -		tpm_buf_append(&buf, options->blobauth, options->blobauth_len);
> +		tpm_buf_append(&sized, options->blobauth, options->blobauth_len);
>  
> -	tpm_buf_append_u16(&buf, payload->key_len);
> -	tpm_buf_append(&buf, payload->key, payload->key_len);
> +	tpm_buf_append_u16(&sized, payload->key_len);
> +	tpm_buf_append(&sized, payload->key, payload->key_len);
> +	tpm_buf_append(&buf, sized.data, sized.length);
>  
>  	/* public */
> -	tpm_buf_append_u16(&buf, 14 + options->policydigest_len);
> -	tpm_buf_append_u16(&buf, TPM_ALG_KEYEDHASH);
> -	tpm_buf_append_u16(&buf, hash);
> +	tpm_buf_reset_sized(&sized);
> +	tpm_buf_append_u16(&sized, TPM_ALG_KEYEDHASH);
> +	tpm_buf_append_u16(&sized, hash);
>  
>  	/* key properties */
>  	flags = 0;
>  	flags |= options->policydigest_len ? 0 : TPM2_OA_USER_WITH_AUTH;
> -	flags |= payload->migratable ? 0 : (TPM2_OA_FIXED_TPM |
> -					    TPM2_OA_FIXED_PARENT);
> -	tpm_buf_append_u32(&buf, flags);
> +	flags |= payload->migratable ? 0 : (TPM2_OA_FIXED_TPM | TPM2_OA_FIXED_PARENT);
> +	tpm_buf_append_u32(&sized, flags);
>  
>  	/* policy */
> -	tpm_buf_append_u16(&buf, options->policydigest_len);
> +	tpm_buf_append_u16(&sized, options->policydigest_len);
>  	if (options->policydigest_len)
> -		tpm_buf_append(&buf, options->policydigest,
> -			       options->policydigest_len);
> +		tpm_buf_append(&sized, options->policydigest, options->policydigest_len);
>  
>  	/* public parameters */
> -	tpm_buf_append_u16(&buf, TPM_ALG_NULL);
> -	tpm_buf_append_u16(&buf, 0);
> +	tpm_buf_append_u16(&sized, TPM_ALG_NULL);
> +	tpm_buf_append_u16(&sized, 0);
> +
> +	tpm_buf_append(&buf, sized.data, sized.length);
>  
>  	/* outside info */
>  	tpm_buf_append_u16(&buf, 0);
> @@ -312,21 +321,20 @@ int tpm2_seal_trusted(struct tpm_chip *chip,
>  	if (rc)
>  		goto out;
>  
> -	blob_len = be32_to_cpup((__be32 *) &buf.data[TPM_HEADER_SIZE]);
> -	if (blob_len > MAX_BLOB_SIZE) {
> +	blob_len = tpm_buf_read_u32(&buf, &offset);
> +	if (blob_len > MAX_BLOB_SIZE || buf.flags & TPM_BUF_BOUNDARY_ERROR) {
>  		rc = -E2BIG;
>  		goto out;
>  	}
> -	if (tpm_buf_length(&buf) < TPM_HEADER_SIZE + 4 + blob_len) {
> +	if (buf.length - offset < blob_len) {
>  		rc = -EFAULT;
>  		goto out;
>  	}
>  
> -	blob_len = tpm2_key_encode(payload, options,
> -				   &buf.data[TPM_HEADER_SIZE + 4],
> -				   blob_len);
> +	blob_len = tpm2_key_encode(payload, options, &buf.data[offset], blob_len);
>  
>  out:
> +	tpm_buf_destroy(&sized);
>  	tpm_buf_destroy(&buf);
>  
>  	if (rc > 0) {
> -- 
> 2.42.1