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SubjectRe: [PATCH] tpm: Actually fail on TPM errors during "get random"
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On Mon, 2019-04-01 at 11:32 -0700, Kees Cook wrote:
[...]
> --- a/drivers/char/tpm/tpm1-cmd.c
> +++ b/drivers/char/tpm/tpm1-cmd.c
> @@ -510,7 +510,7 @@ struct tpm1_get_random_out {
> *
> * Return:
> * * number of bytes read
> - * * -errno or a TPM return code otherwise
> + * * -errno (positive TPM return codes are masked to -EIO)
> */
> int tpm1_get_random(struct tpm_chip *chip, u8 *dest, size_t max)
> {
> @@ -524,7 +524,7 @@ int tpm1_get_random(struct tpm_chip *chip, u8
> *dest, size_t max)
>
> rc = tpm_buf_init(&buf, TPM_TAG_RQU_COMMAND,
> TPM_ORD_GET_RANDOM);
> if (rc)
> - return rc;
> + goto fail;
>
> do {
> tpm_buf_append_u32(&buf, num_bytes);
> @@ -559,7 +559,10 @@ int tpm1_get_random(struct tpm_chip *chip, u8
> *dest, size_t max)
> rc = total ? (int)total : -EIO;
> out:
> tpm_buf_destroy(&buf);
> - return rc;

You can't remove this otherwise the only return will ever be a failure.

I think what you're trying to catch is tpm_transmit_cmd returning a
positive failure, So you need to check the output of tpm_transmit_cmd
as well and goto failure leaving the above return in place.

James


> +fail:
> + if (rc < 0)
> + return rc;
> + return -EIO;
> }
>
> #define TPM_ORD_PCRREAD 21
> --
> 2.17.1
>
>

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