Re: [PATCH v6 8/8] KEYS: trusted: tpm2: Use struct tpm_buf for sized buffers

Stefan Berger
2023-11-27T21:21:13Z

On 11/23/23 21:02, 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>

Reviewed-by: Stefan Berger <stefanb@linux.ibm.com>

> ---
> 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);
> + 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) {