Re: [PATCH] RDMA/siw: Fix missing permission check in user buffer registration

[Jason Gunthorpe <jgg@nvidia.com>]

On Fri, Dec 16, 2022 at 08:11:32PM +0000, Bernard Metzler wrote:
> 
> 
> > -----Original Message-----
> > From: Jason Gunthorpe <jgg@nvidia.com>
> > Sent: Friday, 16 December 2022 19:35
> > To: Bernard Metzler <BMT@zurich.ibm.com>
> > Cc: linux-rdma@vger.kernel.org; leonro@nvidia.com; David.Laight@aculab.com
> > Subject: [EXTERNAL] Re: [PATCH] RDMA/siw: Fix missing permission check in
> > user buffer registration
> > 
> > On Fri, Dec 16, 2022 at 07:32:09PM +0100, Bernard Metzler wrote:
> > > User communication buffer registration lacks check of access
> > > rights for provided address range. Using pin_user_pages_fast()
> > > instead of pin_user_pages() during user page pinning implicitely
> > > introduces the necessary check. It furthermore tries to avoid
> > > grabbing the mmap_read_lock.
> > 
> > Huh? What access check?
> > 
> 
>         if (unlikely(!access_ok((void __user *)start, len)))
>                 return -EFAULT;
> 
> siw needs to call access_ok() during user buffer registration.

No, it doesn't

Either pin_user_pages or pin_user_pages_fast() are equivalent.

You do have a bad bug here if this isn't holding the mmap lock though

Jason