linux-kernel - Re: usb: f_fs: Fix CFI failure in ki

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Message-ID: <Y5cum5pYxro1SYtx@donbot>
Date:   Mon, 12 Dec 2022 13:37:31 +0000
From:   John Keeping <john@...anate.com>
To:     Prashanth K <quic_prashk@...cinc.com>
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "Gustavo A . R . Silva" <gustavoars@...nel.org>,
        Shuah Khan <skhan@...uxfoundation.org>,
        Linyu Yuan <quic_linyyuan@...cinc.com>,
        Pratham Pratap <quic_ppratap@...cinc.com>,
        Vincent Pelletier <plr.vincent@...il.com>,
        Dan Carpenter <error27@...il.com>,
        Udipto Goswami <quic_ugoswami@...cinc.com>,
        linux-usb@...r.kernel.org, linux-kernel@...r.kernel.org,
        "# 5 . 15" <stable@...r.kernel.org>
Subject: Re: usb: f_fs: Fix CFI failure in ki_complete

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@...r.kernel.org> # 5.15
> Signed-off-by: Prashanth K <quic_prashk@...cinc.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 the problem here, ki_complete() is declared with a
long parameter, so won't integer promotion kick in so that the function
is called with a long?  Why is the explicit cast necessary?

>  
>  	if (io_data->ffs->ffs_eventfd && !kiocb_has_eventfd)
>  		eventfd_signal(io_data->ffs->ffs_eventfd, 1);
> -- 
> 2.7.4
>