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

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Date:   Thu, 25 Aug 2016 17:06:10 -0400
From:   Jarkko Sakkinen <jarkko.sakkinen@...ux.intel.com>
To:     Jason Gunthorpe <jgunthorpe@...idianresearch.com>
Cc:     Peter Huewe <peterhuewe@....de>,
        linux-security-module@...r.kernel.org, stable@...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 Thu, Aug 25, 2016 at 12:30:59PM -0600, Jason Gunthorpe wrote:
> On Tue, Aug 23, 2016 at 08:57:22PM -0400, Jarkko Sakkinen wrote:
> 
> > +     if (flags & TPM_TRANSMIT_LOCK)
> > +             mutex_lock(&chip->tpm_mutex);
> 
> I think I would invert this. UNLOCKED is the exceptional case, so I'd
> make the 0 flags lock. If we see UNLOCKED in the caller then we know
> to audit for locking, 0 is much less obvious.

I'm fine with either way.

> > @@ -576,7 +576,7 @@ static int tpm2_load(struct tpm_chip *chip,
> >  		goto out;
> >  	}
> >  
> > -	rc = tpm_transmit_cmd(chip, buf.data, PAGE_SIZE, "loading blob");
> > +	rc = __tpm_transmit_cmd(chip, buf.data, PAGE_SIZE, "loading blob", 0);
> 
> All these points should accept a flags too and the caller should pass
> in the TPM_TRASNMIT_UNLOCKED if it needs it..

For this bug fix it makes sense to implement it the way I did because it
needs to be applied to multiple releases (I think I've underlined this
in my changelog).

If you think this is high priority, I can make the next revision into
patch set of two patches. The second patch would implement the change
you suggested.

/Jarkko