Re: [PATCH rdma-rc] IB/mlx5: Fix use-after-free error while accessing ev_file pointer

[Jason Gunthorpe <jgg@mellanox.com>]

On Thu, Aug 08, 2019 at 06:32:00PM +0300, Yishai Hadas wrote:
> > > diff --git a/drivers/infiniband/hw/mlx5/devx.c b/drivers/infiniband/hw/mlx5/devx.c
> > > index 2d1b3d9609d9..af5bbb35c058 100644
> > > +++ b/drivers/infiniband/hw/mlx5/devx.c
> > > @@ -2644,12 +2644,13 @@ static int devx_async_event_close(struct inode *inode, struct file *filp)
> > >   	struct devx_async_event_file *ev_file = filp->private_data;
> > 
> > This line is wrong, it should be
> > 
> >    	struct devx_async_event_file *ev_file = container_of(struct
> >   	                   devx_async_event_file, filp->private_data, uobj);
> 
> You suggested the below 2 lines instead of the above one line, correct ? as
> struct devx_async_event_file wraps uobj as its first field this is logically
> equal, agree ?

Yes, it is wrong only in the use of the type system, the private_data
void * should only ever be cast to a ib_uobject.

> struct ib_uobject *uobj = filp->private_data;

This could be done with a cast

> > It is also a bit redundant to store the mlx5_ib_dev in the
> > devx_async_event_file as uobj->ucontext->dev is the same pointer.
> >  
> Post hot unplug uobj->ucontext might not be accessible, isn't it ?
> Current code should be fine for that.

That is the other kind of weird thing, all this destruction could be
done on unplug..

> Are we fine to take this patch ?

Yes

Jason