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

[Jarkko Sakkinen]

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