linux-kernel - Re: [GIT PULL] New TPM driver, hwrng driver and fixes

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Date:	Fri, 27 Jul 2012 15:09:17 -0700
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Kent Yoder <key@...ux.vnet.ibm.com>
CC:	James Morris <jmorris@...ei.org>, linux-kernel@...r.kernel.org,
	linux-security-module@...r.kernel.org,
	tpmdd-devel@...ts.sourceforge.net,
	Peter Huewe <peter.huewe@...ineon.com>,
	Bryan Freed <bfreed@...omium.org>,
	David Safford <safford@...ux.vnet.ibm.com>
Subject: Re: [GIT PULL] New TPM driver, hwrng driver and fixes

On 07/27/2012 01:30 PM, Kent Yoder wrote:

> +
> +	do {
> +		tpm_cmd.header.in = tpm_getrandom_header;
> +		tpm_cmd.params.getrandom_in.num_bytes = cpu_to_be32(num_bytes);
> +
> +		err = transmit_cmd(chip, &tpm_cmd,
> +				   TPM_GETRANDOM_RESULT_SIZE + num_bytes,
> +				   "attempting get random");
> +		if (err) {
> +			/* err can be positive if it came from the TPM itself,
> +			 * so return a negative value here instead. */
> +			err = -EFAULT;

-EFAULT is definitely wrong (that means a bad pointer was passed), you
can use -EIO instead.

However, I would suggest:

	err = total ? total : -EIO;

... so you report the number of bytes successfully received if we got
any.  However, since you *also* do that on the retry line,

> +			goto out_err;
> +		}
> +
> +		recd = be32_to_cpu(tpm_cmd.params.getrandom_out.rng_data_len);
> +		memcpy(dest, tpm_cmd.params.getrandom_out.rng_data, recd);
> +
> +		dest += recd;
> +		total += recd;
> +		num_bytes -= recd;
> +	} while (retries-- && total < max);
> +
> +	err = total;

Should we return something other than 0 if we run out of retries here, too?

Perhaps we should just do the same "err = total ? total : -EIO;" here
and the above statement can just turn into a break;.

> -	ret = my_get_random(hash, SHA1_DIGEST_SIZE);
> +	ret = tpm_get_random(TPM_ANY_NUM, hash, SHA1_DIGEST_SIZE);
>  	if (ret < 0)
>  		return ret;

You are still not checking the return values correctly!

This needs to be something like:

	ret = tpm_get_random(TPM_ANY_NUM, hash, SHA1_DIGEST_SIZE);
	if (ret != SHA1_DIGEST_SIZE)
		return -EIO;	/* Or whatever is appropriate here */


	-hpa
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