linux-kernel - Re: [PATCH] scsi: bfa: bfad_attr.c: Cleaning up missing null-terminate after strncpy call

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Message-ID: <1401919181.17510.36.camel@dabdike>
Date:	Wed, 04 Jun 2014 14:59:41 -0700
From:	James Bottomley <James.Bottomley@...senPartnership.com>
To:	Rickard Strandqvist <rickard_strandqvist@...ctrumdigital.se>
Cc:	Anil Gurumurthy <anil.gurumurthy@...gic.com>,
	Sudarsana Kalluru <sudarsana.kalluru@...gic.com>,
	linux-scsi@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] scsi: bfa: bfad_attr.c:  Cleaning up missing
 null-terminate after strncpy call

On Wed, 2014-06-04 at 23:32 +0200, Rickard Strandqvist wrote:
> Added a guaranteed null-terminate after call to strncpy.
> 
> This was partly found using a static code analysis program called cppcheck.
> 
> Signed-off-by: Rickard Strandqvist <rickard_strandqvist@...ctrumdigital.se>
> ---
>  drivers/scsi/bfa/bfad_attr.c |    3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/scsi/bfa/bfad_attr.c b/drivers/scsi/bfa/bfad_attr.c
> index 40be670..06aa3dd 100644
> --- a/drivers/scsi/bfa/bfad_attr.c
> +++ b/drivers/scsi/bfa/bfad_attr.c
> @@ -843,7 +843,8 @@ bfad_im_symbolic_name_show(struct device *dev, struct device_attribute *attr,
>  
>  	bfa_fcs_lport_get_attr(&bfad->bfa_fcs.fabric.bport, &port_attr);
>  	strncpy(symname, port_attr.port_cfg.sym_name.symname,
> -			BFA_SYMNAME_MAXLEN);
> +			sizeof(symname));
> +	symname[sizeof(symname) - 1] = '\0';

So actually, this isn't the correct pattern for this type of potential
problem, where the problem exists, the pattern is to replace strncpy()
with strlcpy() which does a correct null termination on truncation.

In this case I presume your static checker isn't sufficiently clever to
see that there isn't a bug because port_attr.port_cfg.sym_name.symname
is carefully copied to be NULL terminated and always less than
BFA_SYMNAME_MAXLEN, so when copying out of it we can rely on the NULL
termination fitting into BFA_SYMNAME_MAXLEN.

James


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