netdev - Re: [PATCH] caif: replace deprecated strncpy with strscpy

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Message-ID: <CAFhGd8qQ_e_rh1xQqAnaAZmA7R+ftRGjprxGp+njoqg_FGMCSw@mail.gmail.com>
Date: Thu, 12 Sep 2024 13:43:49 -0700
From: Justin Stitt <justinstitt@...gle.com>
To: Simon Horman <horms@...nel.org>
Cc: "David S. Miller" <davem@...emloft.net>, Eric Dumazet <edumazet@...gle.com>, 
	Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>, netdev@...r.kernel.org, 
	linux-kernel@...r.kernel.org, linux-hardening@...r.kernel.org, 
	Kees Cook <kees@...nel.org>
Subject: Re: [PATCH] caif: replace deprecated strncpy with strscpy_pad

Hi,

On Tue, Sep 10, 2024 at 2:37 AM Simon Horman <horms@...nel.org> wrote:
>
> On Mon, Sep 09, 2024 at 04:39:28PM -0700, Justin Stitt wrote:
> > strncpy() is deprecated for use on NUL-terminated destination strings [1] and
> > as such we should prefer more robust and less ambiguous string interfaces.
> >
> > Towards the goal of [2], replace strncpy() with an alternative that
> > guarantees NUL-termination and NUL-padding for the destination buffer.
>
> Hi Justin,
>
> I am curious to know why the _pad variant was chosen.

I chose the _pad variant as it matches the behavior of strncpy in this
context, ensuring minimal functional change. I think the point you're
trying to get at is that the net_device should be zero allocated to
begin with -- rendering all thus NUL-padding superfluous. I have some
questions out of curiosity: 1) do all control paths leading here
zero-allocate the net_device struct? and 2) does it matter that this
private data be NUL-padded (I assume not).

With all that being said, I'd be happy to send a v2 using the regular
strscpy variant if needed.

>
> > Link: https://www.kernel.org/doc/html/latest/process/deprecated.html#strncpy-on-nul-terminated-strings [1]
> > Link: https://github.com/KSPP/linux/issues/90 [2]
> > Link: https://manpages.debian.org/testing/linux-manual-4.8/strscpy.9.en.html
> > Cc: Kees Cook <keescook@...omium.org>
> > Cc: linux-hardening@...r.kernel.org
> > Signed-off-by: Justin Stitt <justinstitt@...gle.com>
> > ---
> > Note: build-tested only.
> > ---
> >  net/caif/chnl_net.c | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/net/caif/chnl_net.c b/net/caif/chnl_net.c
> > index 47901bd4def1..ff37dceefa26 100644
> > --- a/net/caif/chnl_net.c
> > +++ b/net/caif/chnl_net.c
> > @@ -347,7 +347,7 @@ static int chnl_net_init(struct net_device *dev)
> >       struct chnl_net *priv;
> >       ASSERT_RTNL();
> >       priv = netdev_priv(dev);
> > -     strncpy(priv->name, dev->name, sizeof(priv->name));
> > +     strscpy_pad(priv->name, dev->name);
> >       INIT_LIST_HEAD(&priv->list_field);
> >       return 0;
> >  }
> >
> > ---
> > base-commit: bc83b4d1f08695e85e85d36f7b803da58010161d
> > change-id: 20240909-strncpy-net-caif-chnl_net-c-a505e955e697
> >
> > Best regards,
> > --
> > Justin Stitt <justinstitt@...gle.com>
> >
> >

I appreciate the review.

Thanks
Justin