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

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Message-ID: <20201102114903.GN4127@dell>
Date:   Mon, 2 Nov 2020 11:49:03 +0000
From:   Lee Jones <lee.jones@...aro.org>
To:     David Laight <David.Laight@...LAB.COM>
Cc:     "gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>,
        "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, 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/

-- 
Lee Jones [李琼斯]
Senior Technical Lead - Developer Services
Linaro.org │ Open source software for Arm SoCs
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