linux-kernel - Re: [PATCH RFC] tpm: migrate pubek_show to struct tpm

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Date:   Tue, 30 May 2017 07:52:08 +0300
From:   Jarkko Sakkinen <jarkko.sakkinen@...ux.intel.com>
To:     Jason Gunthorpe <jgunthorpe@...idianresearch.com>
Cc:     tpmdd-devel@...ts.sourceforge.net,
        linux-security-module@...r.kernel.org,
        Peter Huewe <peterhuewe@....de>,
        Marcel Selhorst <tpmdd@...horst.net>,
        open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH RFC] tpm: migrate pubek_show to struct tpm_buf

On Thu, May 25, 2017 at 04:40:50PM -0600, Jason Gunthorpe wrote:
> On Thu, May 25, 2017 at 03:28:01PM -0700, Jarkko Sakkinen wrote:
> > On Thu, May 25, 2017 at 03:16:13PM -0600, Jason Gunthorpe wrote:
> > > On Thu, May 25, 2017 at 02:11:04PM -0700, Jarkko Sakkinen wrote:
> > > >  	struct tpm_chip *chip = to_tpm_chip(dev);
> > > > +	char anti_replay[20];
> > > >  
> > > > -	tpm_cmd.header.in = tpm_readpubek_header;
> > > > -	err = tpm_transmit_cmd(chip, NULL, &tpm_cmd, READ_PUBEK_RESULT_SIZE,
> > > > +	rc = tpm_buf_init(&tpm_buf, TPM_TAG_RQU_COMMAND, TPM_ORD_READPUBEK);
> > > > +	if (rc)
> > > > +		return rc;
> > > > +
> > > > +	/* The checksum is ignored so it doesn't matter what the contents are.
> > > > +	 */
> > > > +	tpm_buf_append(&tpm_buf, anti_replay, sizeof(anti_replay));
> > > 
> > > It does matter, we do not want to leak random kernel memory incase it
> > > has something sensitive. Zero anti_replay.
> > 
> > If there was a leak it has existed before this change as tpm_cmd was
> > also allocated from stack. And there is not leak because the checksum is
> > not printed.
> 
> It leaks stack memory to the TPM which is not OK.

Right, of course, vtpm_tpm_proxy.

/Jarkko