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

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

[Lee Jones]

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.

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@enneenne.com>
Cc: "Eurotech S.p.A" <info@eurotech.it>
Reported-by: Geert Uytterhoeven <geert+renesas@glider.be>
Signed-off-by: Lee Jones <lee.jones@linaro.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);
 	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));
 	c2dev->ops = ops;
 	mutex_init(&c2dev->mutex);
 
-- 
2.25.1

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

[Arnd Bergmann]

On Tue, Jul 14, 2020 at 10:33 AM Lee Jones <lee.jones@linaro.org> 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.
>
> 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@enneenne.com>
> Cc: "Eurotech S.p.A" <info@eurotech.it>
> Reported-by: Geert Uytterhoeven <geert+renesas@glider.be>
> Signed-off-by: Lee Jones <lee.jones@linaro.org>

Acked-by: Arnd Bergmann <arnd@arndb.de>

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

[Greg KH]

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@enneenne.com>
> Cc: "Eurotech S.p.A" <info@eurotech.it>
> Reported-by: Geert Uytterhoeven <geert+renesas@glider.be>
> Signed-off-by: Lee Jones <lee.jones@linaro.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