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

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Message-ID: <20160720164818.GA21460@obsidianresearch.com>
Date:	Wed, 20 Jul 2016 10:48:18 -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,
	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 tpm2_unseal_trusted()

On Wed, Jul 20, 2016 at 03:16:32AM +0300, Jarkko Sakkinen wrote:
> Unseal and load operations should be done as an atomic unit. This
> commit fixes the issue by moving TPM mutex handling to tpm_try_get_ops()
> and tpm_put_ops(), which is probably more logical place for it anyway.

No..

'get_ops' is to be used to hold a persisent kref to a single tpm. It
cannot block other tpm access.

Eg a upper protocol might get_ops to for a long period to ensure it
consistently talks to the same TPM in a multi-tpm system.

We need something else to solve whatever you are concerned with
here..

Jason