linux-kernel - Re: [PATCH] tpm: fix a race condition in tpm2_unseal

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Date:   Sun, 28 Aug 2016 12:51:49 -0600
From:   Jason Gunthorpe <jgunthorpe@...idianresearch.com>
To:     Jarkko Sakkinen <jarkko.sakkinen@...ux.intel.com>
Cc:     Peter Huewe <peterhuewe@....de>,
        linux-security-module@...r.kernel.org, stable@...r.kernel.org,
        Marcel Selhorst <tpmdd@...horst.net>,
        "moderated list:TPM DEVICE DRIVER" 
        <tpmdd-devel@...ts.sourceforge.net>,
        open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] tpm: fix a race condition in tpm2_unseal_trusted()

On Sun, Aug 28, 2016 at 08:36:52AM +0200, Jarkko Sakkinen wrote:
>  
> @@ -576,7 +576,8 @@ static int tpm2_load(struct tpm_chip *chip,
>  		goto out;
>  	}
>  
> -	rc = tpm_transmit_cmd(chip, buf.data, PAGE_SIZE, "loading blob");
> +	rc = tpm_transmit_cmd(chip, buf.data, PAGE_SIZE, TPM_TRANSMIT_UNLOCKED,
> +			      "loading blob");

I still don't like this, required mutex's should not be split outside the
function that needs them without more a more obvious indication:

> +	mutex_lock(&chip->tpm_mutex);
>  	rc = tpm2_load(chip, payload, options, &blob_handle);
>  	if (rc)
> -		return rc;

I recommend you stick with the idiom and do this:

        mutex_lock(&chip->tpm_mutex);
  	rc = tpm2_load(chip, payload, options, &blob_handle, TPM_TRANSMIT_UNLOCKED);

Which makes it easy to see we are doing it right everywhere.

Jason