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

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Date:   Thu, 1 Mar 2018 14:10:17 -0800
From:   J Freyensee <why2jjj.linux@...il.com>
To:     Jarkko Sakkinen <jarkko.sakkinen@...ux.intel.com>,
        linux-integrity@...r.kernel.org
Cc:     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

.
.
.
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