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Subject: Re: [PATCH] ima: use struct_size() in kzalloc()
From:   Mimi Zohar <zohar@linux.ibm.com>
To:     "Gustavo A. R. Silva" <gustavo@embeddedor.com>,
        Dmitry Kasatkin <dmitry.kasatkin@gmail.com>,
        James Morris <jmorris@namei.org>,
        "Serge E. Hallyn" <serge@hallyn.com>
Cc:     linux-integrity@vger.kernel.org,
        linux-security-module@vger.kernel.org, linux-kernel@vger.kernel.org
Date:   Wed, 28 Aug 2019 23:45:55 -0400
In-Reply-To: <671185b9-5c91-5235-b5ea-96d3449bf716@embeddedor.com>
References: <20190529165343.GA2584@embeddedor>
         <671185b9-5c91-5235-b5ea-96d3449bf716@embeddedor.com>
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Hi Gustavo,

On Wed, 2019-08-28 at 13:29 -0500, Gustavo A. R. Silva wrote:
> On 5/29/19 11:53 AM, Gustavo A. R. Silva wrote:
> > One of the more common cases of allocation size calculations is finding
> > the size of a structure that has a zero-sized array at the end, along
> > with memory for some number of elements for that array. For example:
> > 
> > struct foo {
> >    int stuff;
> >    struct boo entry[];
> > };
> > 
> > instance = kzalloc(sizeof(struct foo) + count * sizeof(struct boo), GFP_KERNEL);
> > 
> > Instead of leaving these open-coded and prone to type mistakes, we can
> > now use the new struct_size() helper:
> > 
> > instance = kzalloc(struct_size(instance, entry, count), GFP_KERNEL);
> > 
> > This code was detected with the help of Coccinelle.
> > 
> > Signed-off-by: Gustavo A. R. Silva <gustavo@embeddedor.com>
> > ---
> >  security/integrity/ima/ima_template.c | 5 ++---
> >  1 file changed, 2 insertions(+), 3 deletions(-)
> > 
> > diff --git a/security/integrity/ima/ima_template.c b/security/integrity/ima/ima_template.c
> > index b631b8bc7624..b945dff2ed14 100644
> > --- a/security/integrity/ima/ima_template.c
> > +++ b/security/integrity/ima/ima_template.c
> > @@ -281,9 +281,8 @@ static int ima_restore_template_data(struct ima_template_desc *template_desc,
> >  	int ret = 0;
> >  	int i;
> >  
> > -	*entry = kzalloc(sizeof(**entry) +
> > -		    template_desc->num_fields * sizeof(struct ima_field_data),
> > -		    GFP_NOFS);
> > +	*entry = kzalloc(struct_size(*entry, template_data,
> > +				     template_desc->num_fields), GFP_NOFS);
> >  	if (!*entry)
> >  		return -ENOMEM;
> >  
> > 

The same usage exists in ima_api.c: ima_alloc_init_template().  Did
you want to make the change there as well?

thanks,

Mimi