Re: usb: f_fs: Fix CFI failure in ki_complete

[Greg Kroah-Hartman <gregkh@linuxfoundation.org>]

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.

"might"?  Does it or not?  If it does, why hasn't this been reported
before?

> Cc: <stable@vger.kernel.org> # 5.15

CFI first showed up in 6.1, not 5.15, right?

> 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);

Why just fix up this one instance?  What about ep_user_copy_worker()?
And what about all other calls to ki_complete that are not using a
(long) cast?

This feels wrong, what exactly is the reported error and how come other
kernel calls to this function pointer have not had a problem with CFI?
ceph_aio_complete() would be another example, right?

thanks,

greg k-h