linux-kernel - Re: [PATCH 3/5] tpm: migrate tpm2_probe() to use struct tpm

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Date:   Mon, 5 Mar 2018 13:11:07 +0200
From:   Jarkko Sakkinen <jarkko.sakkinen@...ux.intel.com>
To:     J Freyensee <why2jjj.linux@...il.com>
Cc:     linux-integrity@...r.kernel.org,
        linux-security-module@...r.kernel.org, keyrings@...r.kernel.org,
        Peter Huewe <peterhuewe@....de>,
        Jason Gunthorpe <jgg@...pe.ca>, Arnd Bergmann <arnd@...db.de>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 3/5] tpm: migrate tpm2_probe() to use struct tpm_buf

On Thu, Mar 01, 2018 at 02:10:17PM -0800, J Freyensee wrote:
> .
> .
> .
> I'm new to this area of the kernel, but I'm not getting these lines:
> 
> > +	rc = tpm_transmit_cmd(chip, NULL, buf.data, PAGE_SIZE, 0, 0, NULL);
> > +	tpm_buf_destroy(&buf);
> >   	if (rc <  0)
> Why is this if() check not directly after the tpm_transmit_cmd() call that
> sets rc?  Is it correct you want to destroy buf regardless of the
> tpm_transmit_cmd() outcome?
> >   		return rc;
> > -
> > -	if (be16_to_cpu(cmd.header.out.tag) == TPM2_ST_NO_SESSIONS)
> > +	out = (struct tpm_output_header *)buf.data;
> 
> So buf has been destroyed, buf.data sill has something valid to assign to
> out?
> > +	if (be16_to_cpu(out->tag) == TPM2_ST_NO_SESSIONS)
> >   		chip->flags |= TPM_CHIP_FLAG_TPM2;
> >   	return 0;
> Thanks,
> Jay

Nope it is a regression in the patch. Thank you :-) tpm_buf_destroy()
can be called if the response data is not needed other than everything
went OK (tpm_transmit_cmd() already digs this info).

/Jarkko