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

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Message-ID: <20200723074115.GA1289884@kroah.com>
Date:   Thu, 23 Jul 2020 09:41:15 +0200
From:   Greg KH <gregkh@...uxfoundation.org>
To:     Lee Jones <lee.jones@...aro.org>
Cc:     arnd@...db.de, linux-arm-kernel@...ts.infradead.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 1/1] misc: c2port: core: Make copying name from userspace
 more secure

On Tue, Jul 14, 2020 at 09:32:59AM +0100, Lee Jones wrote:
> Currently the 'c2dev' device data is not zeroed when its allocated.
> Coupled with the fact strncpy() *may not* provide a NUL terminator
> means that a 1-byte leak would be possible *if* this was ever copied
> to userspace.

c2dev is a kernel internal structure, it is never copied to userspace,
so why even mention such a thing?

> To prevent such a failing, let's first ensure the 'c2dev' device data
> area is fully zeroed out and 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>
> Signed-off-by: Lee Jones <lee.jones@...aro.org>
> ---
>  drivers/misc/c2port/core.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/misc/c2port/core.c b/drivers/misc/c2port/core.c
> index 80d87e8a0bea9..0de538a1cc1c6 100644
> --- a/drivers/misc/c2port/core.c
> +++ b/drivers/misc/c2port/core.c
> @@ -899,7 +899,7 @@ struct c2port_device *c2port_device_register(char *name,
>  		unlikely(!ops->c2d_get) || unlikely(!ops->c2d_set))
>  		return ERR_PTR(-EINVAL);
>  
> -	c2dev = kmalloc(sizeof(struct c2port_device), GFP_KERNEL);
> +	c2dev = kzalloc(sizeof(struct c2port_device), GFP_KERNEL);

All fields seem to be properly initialized so this really isn't needed
from what I can tell.

>  	if (unlikely(!c2dev))
>  		return ERR_PTR(-ENOMEM);
>  
> @@ -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));

Given there is only 1 user of this function, and it passes in "uc", this
isn't a big deal :)

But, I can take this as a separate patch, if you want to redo this, just
to be safe in the future.

thanks,

greg k-h