[PATCH] dma-buf: heaps: Fix off-by-one in CMA heap fault handler

[John Stultz]

On Fri, Aug 30, 2024 at 12:26 PM T.J. Mercier <tjmercier at google.com> wrote:
>
> Until VM_DONTEXPAND was added in commit 1c1914d6e8c6 ("dma-buf: heaps:
> Don't track CMA dma-buf pages under RssFile") it was possible to obtain
> a mapping larger than the buffer size via mremap and bypass the overflow
> check in dma_buf_mmap_internal. When using such a mapping to attempt to
> fault past the end of the buffer, the CMA heap fault handler also checks
> the fault offset against the buffer size, but gets the boundary wrong by
> 1. Fix the boundary check so that we don't read off the end of the pages
> array and insert an arbitrary page in the mapping.
>
> Reported-by: Xingyu Jin <xingyuj at google.com>
> Fixes: a5d2d29e24be ("dma-buf: heaps: Move heap-helper logic into the cma_heap implementation")
> Cc: stable at vger.kernel.org # Applicable >= 5.10. Needs adjustments only for 5.10.
> Signed-off-by: T.J. Mercier <tjmercier at google.com>
> ---
>  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 c384004b918e..93be88b805fe 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;


Thanks for fixing this! (And thanks to Xingyu Jin for catching it!)

Acked-by: John Stultz <jstultz at google.com>

thanks
-john