linux-hardening - Re: [PATCH v4 2/3] drivers/soc/renesas: Prefer memcpy over strcpy

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Date:   Tue, 10 Aug 2021 17:59:53 +0200
From:   Len Baker <len.baker@....com>
To:     Christophe JAILLET <christophe.jaillet@...adoo.fr>,
        Bernd Petrovitsch <bernd@...rovitsch.priv.at>
Cc:     Andy Gross <agross@...nel.org>,
        Bjorn Andersson <bjorn.andersson@...aro.org>,
        Geert Uytterhoeven <geert+renesas@...der.be>,
        Magnus Damm <magnus.damm@...il.com>,
        Santosh Shilimkar <ssantosh@...nel.org>,
        Len Baker <len.baker@....com>,
        Kees Cook <keescook@...omium.org>,
        David Laight <David.Laight@...LAB.COM>,
        Robin Murphy <robin.murphy@....com>,
        linux-hardening@...r.kernel.org, linux-arm-msm@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-renesas-soc@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH v4 2/3] drivers/soc/renesas: Prefer memcpy over strcpy

Hi,

On Sun, Aug 08, 2021 at 07:06:30PM +0200, Christophe JAILLET wrote:
> Hi,
>
> Le 08/08/2021 à 17:35, Bernd Petrovitsch a écrit :
> > Hi all!
> >
> > On 08/08/2021 14:50, Len Baker wrote:
> > > strcpy() performs no bounds checking on the destination buffer. This
> > > could result in linear overflows beyond the end of the buffer, leading
> > > to all kinds of misbehaviors. So, use memcpy() as a safe replacement.
> > >
> > > This is a previous step in the path to remove the strcpy() function
> > > entirely from the kernel.
> > >
> > > Signed-off-by: Len Baker <len.baker@....com>
> > > ---
> > >   drivers/soc/renesas/r8a779a0-sysc.c | 6 ++++--
> > >   drivers/soc/renesas/rcar-sysc.c     | 6 ++++--
> > >   2 files changed, 8 insertions(+), 4 deletions(-)
> > >
> > > diff --git a/drivers/soc/renesas/r8a779a0-sysc.c b/drivers/soc/renesas/r8a779a0-sysc.c
> > > index d464ffa1be33..7410b9fa9846 100644
> > > --- a/drivers/soc/renesas/r8a779a0-sysc.c
> > > +++ b/drivers/soc/renesas/r8a779a0-sysc.c
> > > @@ -404,19 +404,21 @@ static int __init r8a779a0_sysc_pd_init(void)
> > >   	for (i = 0; i < info->num_areas; i++) {
> > >   		const struct r8a779a0_sysc_area *area = &info->areas[i];
> > >   		struct r8a779a0_sysc_pd *pd;
> > > +		size_t n;
> > >
> > >   		if (!area->name) {
> > >   			/* Skip NULLified area */
> > >   			continue;
> > >   		}
> > >
> > > -		pd = kzalloc(sizeof(*pd) + strlen(area->name) + 1, GFP_KERNEL);
> > > +		n = strlen(area->name) + 1;
> > > +		pd = kzalloc(sizeof(*pd) + n, GFP_KERNEL);
> > Zeroing the allocated bytes is not needed since it's completly
> > overwritten with the strcpy()/memcpy().
>
> The strcpy()/memcpy() only overwrites the pd->name field, not the whole pd
> structure.

You are right.

> I think that it is needed to keep the kzalloc.

Yes, I think so. The kzalloc is needed to guarantee that the whole struct is
initialize (all the members are initialized with zeros).

Regards,
Len

>
> Just my 2c,
> CJ
>
> > >   		if (!pd) {
> > >   			error = -ENOMEM;
> > >   			goto out_put;
> > >   		}
> > >
> > > -		strcpy(pd->name, area->name);
> > > +		memcpy(pd->name, area->name, n);
> > >   		pd->genpd.name = pd->name;
> > >   		pd->pdr = area->pdr;
> > >   		pd->flags = area->flags;
> >
> > And similar for the second hunk.
> >
> > MfG,
> > 	Bernd
> >
>