Re: Changing vma->vm_file in dma_buf_mmap()

[Christian König]

Am 14.09.20 um 16:06 schrieb Jason Gunthorpe:
> On Mon, Sep 14, 2020 at 03:30:47PM +0200, Christian König wrote:
> > Am 14.09.20 um 15:29 schrieb Christian König:
> > > Hi Andrew,
> > >
> > > I'm the new DMA-buf maintainer and Daniel and others came up with
> > > patches extending the use of the dma_buf_mmap() function.
> > >
> > > Now this function is doing something a bit odd by changing the
> > > vma->vm_file while installing a VMA in the mmap() system call
> It doesn't look obviously safe as mmap_region() has an interesting mix
> of file and vma->file
>
> Eg it calls mapping_unmap_writable() using both routes

Thanks for the hint, going to take a look at that code tomorrow.

> What about security? Is it OK that some other random file, maybe in
> another process, is being linked to this mmap?

Good question, I have no idea. That's why I send out this mail.

> > > The background here is that DMA-buf allows device drivers to
> > > export buffer which are then imported into another device
> > > driver. The mmap() handler of the importing device driver then
> > > find that the pgoff belongs to the exporting device and so
> > > redirects the mmap() call there.
> So the pgoff is some virtualized thing?

Yes, absolutely.

Christian.

> Jason