[PATCH] dma-buf: heaps: Fix off by one in cma_heap_vm_fault()

[Dan Carpenter]

On Mon, Oct 02, 2023 at 10:16:24AM -0700, T.J. Mercier wrote:
> On Mon, Oct 2, 2023 at 12:04 AM Dan Carpenter <dan.carpenter at linaro.org> wrote:
> >
> > The buffer->pages[] has "buffer->pagecount" elements so this > comparison
> > has to be changed to >= to avoid reading beyond the end of the array.
> > The buffer->pages[] array is allocated in cma_heap_allocate().
> >
> > Fixes: a5d2d29e24be ("dma-buf: heaps: Move heap-helper logic into the cma_heap implementation")
> > Signed-off-by: Dan Carpenter <dan.carpenter at linaro.org>
> > ---
> >  drivers/dma-buf/heaps/cma_heap.c | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/drivers/dma-buf/heaps/cma_heap.c b/drivers/dma-buf/heaps/cma_heap.c
> > index ee899f8e6721..bea7e574f916 100644
> > --- a/drivers/dma-buf/heaps/cma_heap.c
> > +++ b/drivers/dma-buf/heaps/cma_heap.c
> > @@ -165,7 +165,7 @@ static vm_fault_t cma_heap_vm_fault(struct vm_fault *vmf)
> >         struct vm_area_struct *vma = vmf->vma;
> >         struct cma_heap_buffer *buffer = vma->vm_private_data;
> >
> > -       if (vmf->pgoff > buffer->pagecount)
> > +       if (vmf->pgoff >= buffer->pagecount)
> >                 return VM_FAULT_SIGBUS;
> >
> Hi Dan,
> 
> Your fix looks correct to me, but I'm curious if you observed this
> problem on a device? The mmap in dma-buf.c looks like it prevents
> creating a mapping that is too large, and I think an access beyond the
> VMA should segfault before reaching here.

This is from static analysis and not from testing.  You could be correct
that this bug can't affect real life.

regards,
dan carpenter