Re: usb: f_fs: Fix CFI failure in ki_complete

[Dan Carpenter <error27@gmail.com>]

On Mon, Dec 12, 2022 at 06:54:24PM +0530, Prashanth K wrote:
> Function pointer ki_complete() expects 'long' as its second
> argument, but we pass integer from ffs_user_copy_worker. This
> might cause a CFI failure, as ki_complete is an indirect call
> with mismatched prototype. Fix this by typecasting the second
> argument to long.
> 
> Cc: <stable@vger.kernel.org> # 5.15
> Signed-off-by: Prashanth K <quic_prashk@quicinc.com>
> 
> ---
>  drivers/usb/gadget/function/f_fs.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/usb/gadget/function/f_fs.c b/drivers/usb/gadget/function/f_fs.c
> index 73dc10a7..9c26561 100644
> --- a/drivers/usb/gadget/function/f_fs.c
> +++ b/drivers/usb/gadget/function/f_fs.c
> @@ -835,7 +835,7 @@ static void ffs_user_copy_worker(struct work_struct *work)
>  		kthread_unuse_mm(io_data->mm);
>  	}
>  
> -	io_data->kiocb->ki_complete(io_data->kiocb, ret);
> +	io_data->kiocb->ki_complete(io_data->kiocb, (long)ret);

I don't understand this commit at all.  CFI is Control Flow Integrity
or Common Flash Interface depending on which subsystem we're talking
about.

I really think that Clang needs to be fixed if this really causes an
issue for Clang.  How on earth are we going to know where to add all
the casts?

The commit message says "this might cause a CFI" failure.  Either it
does or it doesn't.  Please someone test this so we can know what's
going on.

Why is it backported to 5.15?  I thought CFI was not going to backported
that far and I has seen people complaining about CFI backports.

regards,
dan carpenter