linux-kernel - Re: [PATCH 1/2] misc: c2port: core: Make copying name from userspace more secure

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Message-ID: <20201102121150.GA663356@kroah.com>
Date:   Mon, 2 Nov 2020 13:11:50 +0100
From:   "gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>
To:     Lee Jones <lee.jones@...aro.org>
Cc:     David Laight <David.Laight@...lab.com>,
        "arnd@...db.de" <arnd@...db.de>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Rodolfo Giometti <giometti@...eenne.com>,
        "Eurotech S.p.A" <info@...otech.it>,
        Geert Uytterhoeven <geert+renesas@...der.be>
Subject: Re: [PATCH 1/2] misc: c2port: core: Make copying name from userspace
 more secure

On Mon, Nov 02, 2020 at 11:49:03AM +0000, Lee Jones wrote:
> On Mon, 02 Nov 2020, David Laight wrote:
> 
> > From: Lee Jones
> > > Sent: 02 November 2020 11:12
> > > 
> > > strncpy() may not provide a NUL terminator, which means that a 1-byte
> > > leak would be possible *if* this was ever copied to userspace.  Ensure
> > > the buffer will always be NUL terminated by using the kernel's
> > > strscpy() which a) uses the destination (instead of the source) size
> > > as the bytes to copy and b) is *always* NUL terminated.
> > > 
> > > Cc: Rodolfo Giometti <giometti@...eenne.com>
> > > Cc: "Eurotech S.p.A" <info@...otech.it>
> > > Reported-by: Geert Uytterhoeven <geert+renesas@...der.be>
> > > Acked-by: Arnd Bergmann <arnd@...db.de>
> > > Signed-off-by: Lee Jones <lee.jones@...aro.org>
> > > ---
> > >  drivers/misc/c2port/core.c | 2 +-
> > >  1 file changed, 1 insertion(+), 1 deletion(-)
> > > 
> > > diff --git a/drivers/misc/c2port/core.c b/drivers/misc/c2port/core.c
> > > index 80d87e8a0bea9..b96444ec94c7e 100644
> > > --- a/drivers/misc/c2port/core.c
> > > +++ b/drivers/misc/c2port/core.c
> > > @@ -923,7 +923,7 @@ struct c2port_device *c2port_device_register(char *name,
> > >  	}
> > >  	dev_set_drvdata(c2dev->dev, c2dev);
> > > 
> > > -	strncpy(c2dev->name, name, C2PORT_NAME_LEN - 1);
> > > +	strscpy(c2dev->name, name, sizeof(c2dev->name));
> > 
> > strscpy() doesn't zero fill so if the memory isn't zeroed
> > and a 'blind' copy to user of the structure is done
> > then more data is leaked.
> > 
> > strscpy() may be better, but rational isn't right.
> 
> The original patch zeroed the data too, but I was asked to remove that
> part [0].  In your opinion, should it be reinstated?
> 
> [0] https://lore.kernel.org/patchwork/patch/1272290/

Just keep the kzalloc() part of the patch, this portion makes no sense
to me.  But if you REALLY want to get it correct, call dev_set_name()
instead please, as that is what it is there for.

thanks,

greg k-h