Re: [PATCH v2 2/6] Input: joystick - use usb_make_subpath()

[Alejandro Colomar <alx+linux-hardening@kernel.org>]

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Hi Shihuang,

> Date: 2026-10-21 20:31:42+0800
> From: Shihuang Liu <shlomojune6@gmail.com>
>
> The pxrc and xpad drivers build their input device physical paths
> by appending "/input0" with strlcat() after usb_make_path().
> 
> In preparation for removing the deprecated strlcat() API [1],
> replace each pair of calls with usb_make_subpath(). The helper
> formats the USB path and the "input0" subpath in one call,
> avoiding a separate buffer scan and append operation.
> 
> Link: https://github.com/KSPP/linux/issues/370 [1]
> Signed-off-by: Shihuang Liu <shlomojune6@gmail.com>
> ---
>  drivers/input/joystick/pxrc.c | 3 +--
>  drivers/input/joystick/xpad.c | 3 +--
>  2 files changed, 2 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/input/joystick/pxrc.c b/drivers/input/joystick/pxrc.c
> index 52d9eab667b7a..1a11e73d7cd04 100644
> --- a/drivers/input/joystick/pxrc.c
> +++ b/drivers/input/joystick/pxrc.c
> @@ -169,8 +169,7 @@ static int pxrc_probe(struct usb_interface *intf,
>  
>  	pxrc->input->name = "PXRC Flight Controller Adapter";
>  
> -	usb_make_path(udev, pxrc->phys, sizeof(pxrc->phys));
> -	strlcat(pxrc->phys, "/input0", sizeof(pxrc->phys));
> +	usb_make_subpath(udev, pxrc->phys, sizeof(pxrc->phys), "input0");

To be honest, I think the composed approach is more readable.  You don't
need to learn a new _subpath function with all the details it has.

Everyone knows what a str*cat() (or str*cpy, FWIW) function does.

I'd rather improve this by adding strscat().  The reason for removing
strlcat(3) is that it is vulnerable to DoS, and that it is inefficient,
but it is good at producing readable code, and a replacement should not
degrade that.


Have a lovely day!
Alex

>  	pxrc->input->phys = pxrc->phys;
>  
>  	usb_to_input_id(udev, &pxrc->input->id);
> diff --git a/drivers/input/joystick/xpad.c b/drivers/input/joystick/xpad.c
> index feb8f368f834e..0f7ca5adaeee7 100644
> --- a/drivers/input/joystick/xpad.c
> +++ b/drivers/input/joystick/xpad.c
> @@ -2059,8 +2059,7 @@ static int xpad_probe(struct usb_interface *intf, const struct usb_device_id *id
>  	if (!xpad)
>  		return -ENOMEM;
>  
> -	usb_make_path(udev, xpad->phys, sizeof(xpad->phys));
> -	strlcat(xpad->phys, "/input0", sizeof(xpad->phys));
> +	usb_make_subpath(udev, xpad->phys, sizeof(xpad->phys), "input0");
>  
>  	xpad->idata = usb_alloc_coherent(udev, XPAD_PKT_LEN,
>  					 GFP_KERNEL, &xpad->idata_dma);
> -- 
> 2.43.0
> 
> 

-- 
<https://www.alejandro-colomar.es>

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