linux-kernel - Re: [PATCH v4 4/9] cxl/mem: Add basic IOCTL interface

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Date:   Wed, 17 Feb 2021 09:55:24 +0000
From:   Jonathan Cameron <Jonathan.Cameron@...wei.com>
To:     Ben Widawsky <ben.widawsky@...el.com>
CC:     <linux-cxl@...r.kernel.org>, <linux-acpi@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>, <linux-nvdimm@...ts.01.org>,
        <linux-pci@...r.kernel.org>, Bjorn Helgaas <helgaas@...nel.org>,
        "Chris Browy" <cbrowy@...ry-design.com>,
        Christoph Hellwig <hch@...radead.org>,
        "Dan Williams" <dan.j.williams@...el.com>,
        David Hildenbrand <david@...hat.com>,
        David Rientjes <rientjes@...gle.com>,
        Ira Weiny <ira.weiny@...el.com>,
        "Jon Masters" <jcm@...masters.org>,
        Rafael Wysocki <rafael.j.wysocki@...el.com>,
        Randy Dunlap <rdunlap@...radead.org>,
        Vishal Verma <vishal.l.verma@...el.com>,
        "John Groves (jgroves)" <jgroves@...ron.com>,
        "Kelley, Sean V" <sean.v.kelley@...el.com>,
        kernel test robot <lkp@...el.com>
Subject: Re: [PATCH v4 4/9] cxl/mem: Add basic IOCTL interface

On Tue, 16 Feb 2021 10:34:32 -0800
Ben Widawsky <ben.widawsky@...el.com> wrote:

...

> > > diff --git a/drivers/cxl/mem.c b/drivers/cxl/mem.c
> > > index 237b956f0be0..4ca4f5afd9d2 100644
> > > --- a/drivers/cxl/mem.c
> > > +++ b/drivers/cxl/mem.c
> > > @@ -686,7 +686,11 @@ static int cxl_validate_cmd_from_user(struct cxl_mem *cxlm,
> > > 
> > >         memcpy(out_cmd, c, sizeof(*c));
> > >         out_cmd->info.size_in = send_cmd->in.size;
> > > -       out_cmd->info.size_out = send_cmd->out.size;
> > > +       /*
> > > +        * XXX: out_cmd->info.size_out will be controlled by the driver, and the
> > > +        * specified number of bytes @send_cmd->out.size will be copied back out
> > > +        * to userspace.
> > > +        */
> > > 
> > >         return 0;
> > >  }  
> > 
> > This deals with the buffer overflow being triggered from userspace.
> > 
> > I'm still nervous.  I really don't like assuming hardware will do the right
> > thing and never send us more data than we expect.
> > 
> > Given the check that it will fit in the target buffer is simple,
> > I'd prefer to harden it and know we can't have a problem.
> > 
> > Jonathan  
> 
> I'm working on hardening __cxl_mem_mbox_send_cmd now per your request. With
> that, I think this solves the issue, right?

Should do.  Thanks,

Jonathan