Re: usb: f_fs: Fix CFI failure in ki_complete

[Prashanth K]

On 12-12-22 07:05 pm, Greg Kroah-Hartman wrote:
> 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?
Sorry for the confusion in commit text, We caught a CFI (Control Flow 
Integrity) failure internally on 5.15, hence pushed this patch. But 
later I came to know that CFI was implemented on 5.4 kernel for Android. 
Will push the same on ACK and share the related details there.

Thanks.
> > Cc: <stable@xxxxxxxxxxxxxxx> # 5.15
>
> CFI first showed up in 6.1, not 5.15, right?
>
> > Signed-off-by: Prashanth K <quic_prashk@xxxxxxxxxxx>
> >
> > ---
> >   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