On Mon 05-10-20 14:38:54, Jason Gunthorpe wrote:
> When get_vaddr_frames() does its hacky follow_pfn() loop it should never
> be allowed to extract a struct page from a normal VMA. This could allow a
> serious use-after-free problem on any kernel memory.
>
> Restrict this to only work on VMA's with one of VM_IO | VM_PFNMAP
> set. This limits the use-after-free problem to only IO memory, which while
> still serious, is an improvement.
>
> Cc: stable@xxxxxxxxxxxxxxx
> Fixes: 8025e5ddf9c1 ("[media] mm: Provide new get_vaddr_frames() helper")
> Signed-off-by: Jason Gunthorpe <jgg@xxxxxxxxxx>
> ---
> mm/frame_vector.c | 4 ++++
> 1 file changed, 4 insertions(+)
>
> diff --git a/mm/frame_vector.c b/mm/frame_vector.c
> index 10f82d5643b6de..26cb20544b6c37 100644
> --- a/mm/frame_vector.c
> +++ b/mm/frame_vector.c
> @@ -99,6 +99,10 @@ int get_vaddr_frames(unsigned long start, unsigned int nr_frames,
> if (ret >= nr_frames || start < vma->vm_end)
> break;
> vma = find_vma_intersection(mm, start, start + 1);
> + if (!(vma->vm_flags & (VM_IO | VM_PFNMAP))) {
> + ret = -EINVAL;
> + goto out;
> + }
> } while (vma && vma->vm_flags & (VM_IO | VM_PFNMAP));
Hum, I fail to see how this helps. If vma has no VM_IO or VM_PFNMAP flag,
we'd exit the loop (to out: label) anyway due to the loop termination
condition and why not return the frames we already have? Furthermore
find_vma_intersection() can return NULL which would oops in your check
then. What am I missing?
Honza
> out:
> if (locked)
> --
> 2.28.0
>
--
Jan Kara <jack@xxxxxxxx>
SUSE Labs, CR
