Re: [PATCH] usb: gadget: f_ncm: Fix NPE in ncm_bind error path

[Greg KH <gregkh@linuxfoundation.org>]

On Thu, Sep 04, 2025 at 07:46:13PM +0800, Kuen-Han Tsai wrote:
> When an ncm_bind/unbind cycle occurs, the ncm->notify_req pointer is
> left pointing to a stale address. If a subsequent call to ncm_bind()
> fails to allocate the endpoints, the function jumps to the unified error
> label. The cleanup code sees the stale ncm->notify_req pointer and calls
> usb_ep_free_request().
> 
> This results in a NPE because it attempts to access the free_request
> function through the endpoint's operations table (ep->ops), which is
> NULL.
> 
> Refactor the error path to use cascading goto labels, ensuring that
> resources are freed in reverse order of allocation. Besides, explicitly
> set pointers to NULL after freeing them.

Why must the pointers be set to NULL?  What is checking and requiring
that?

And this unwinding is tailor-made for the guard() type of logic, why not
convert this code to do that instead, which will fix all of these bugs
automatically, right?

thanks,

greg k-h