linux-kernel - Re: [tpmdd-devel] [PATCH] tpm: fix a sparse error in tpm-interface.c

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Date:   Tue, 31 Jan 2017 22:52:09 +0200
From:   Jarkko Sakkinen <jarkko.sakkinen@...ux.intel.com>
To:     James Bottomley <James.Bottomley@...senPartnership.com>
Cc:     tpmdd-devel@...ts.sourceforge.net,
        open list <linux-kernel@...r.kernel.org>,
        linux-security-module@...r.kernel.org
Subject: Re: [tpmdd-devel] [PATCH] tpm: fix a sparse error in tpm-interface.c

On Tue, Jan 31, 2017 at 11:10:41AM -0800, James Bottomley wrote:
> On Tue, 2017-01-31 at 20:07 +0200, Jarkko Sakkinen wrote:
> > drivers/char/tpm//tpm-interface.c:492:42: warning: bad assignment (
> > -=)
> > to restricted __be32
> > 
> > Fixes: 0883743825e3 ("TPM: sysfs functions consolidation")
> > Signed-off-by: Jarkko Sakkinen <jarkko.sakkinen@...ux.intel.com>
> > ---
> >  drivers/char/tpm/tpm-interface.c | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> > 
> > diff --git a/drivers/char/tpm/tpm-interface.c b/drivers/char/tpm/tpm
> > -interface.c
> > index 423938e..746bc54 100644
> > --- a/drivers/char/tpm/tpm-interface.c
> > +++ b/drivers/char/tpm/tpm-interface.c
> > @@ -489,7 +489,7 @@ ssize_t tpm_getcap(struct tpm_chip *chip, u32
> > subcap_id, cap_t *cap,
> >  		tpm_cmd.params.getcap_in.cap =
> > cpu_to_be32(subcap_id);
> >  		/*subcap field not necessary */
> >  		tpm_cmd.params.getcap_in.subcap_size =
> > cpu_to_be32(0);
> > -		tpm_cmd.header.in.length -=
> > cpu_to_be32(sizeof(__be32));
> > +		tpm_cmd.header.in.length = cpu_to_be32(18);
> 
> using bare numbers here without comment isn't really best practice. 
>  What about setting header.in.length in both legs of the if() to either
> 
> tpm_cmd.header.in.length = cpu_to_be32(HEADER_SIZE + sizeof(struct tpm_getcap_params_in))
> 
> or 
> 
> /* setting subcap_size to zero allows us to elimnate the subcap field */
> tpm_cmd.header.in.length = cpu_to_be32(HEADER_SIZE + sizeof(struct tpm_getcap_params_in) - sizeof(tpm_cmd.params.getcap_in.subcap))

Yeah, also the commit message should be updated rather than
referring to the static checking tool. I'll update the commit
along the lines you proposed...

/Jarkko