linux-kernel - Re: [PATCH] device_core: check null pointer

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Message-ID: <2025111523-preface-scoreless-b478@gregkh>
Date: Sat, 15 Nov 2025 15:16:43 -0500
From: Greg KH <gregkh@...uxfoundation.org>
To: Zhengqiao Xia <xiazhengqiao@...qin.corp-partner.google.com>
Cc: rafael@...nel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] device_core: check null pointer

On Fri, Nov 14, 2025 at 10:18:21PM +0800, Zhengqiao Xia wrote:
> Add null pointer check to avoid null pointer.
> When the USB device's interface is disabled, 'device_add' will not
> be called, and 'dev->p' will be NULL.

Wait, how does that happen?  Shouldn't we prevent that?

> When you use 'usbdev_ioctl' to
> call this USB interface at this point,'__device_attach' will be invoked.
> Then a null pointer will be generated.
> 
> Signed-off-by: Zhengqiao Xia <xiazhengqiao@...qin.corp-partner.google.com>

Not a valid email address :( 

> ---
>  drivers/base/dd.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/base/dd.c b/drivers/base/dd.c
> index 3328101e0e106..cfdeb420fd12a 100644
> --- a/drivers/base/dd.c
> +++ b/drivers/base/dd.c
> @@ -1033,7 +1033,7 @@ static int __device_attach(struct device *dev, bool allow_async)
>  	bool async = false;
>  
>  	device_lock(dev);
> -	if (dev->p->dead) {
> +	if (dev->p && dev->p->dead) {

If dev->p is NULL here, something else went wrong with the caller,
please, let's fix the root problem here instead.

What suddenly changed to cause this to happen?

thanks,

greg k-h