On Mon, Oct 5, 2020 at 7:58 PM Jason Gunthorpe jgg@nvidia.com wrote:
On Mon, Oct 05, 2020 at 07:53:08PM +0200, Jan Kara wrote:
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@vger.kernel.org Fixes: 8025e5ddf9c1 ("[media] mm: Provide new get_vaddr_frames() helper") Signed-off-by: Jason Gunthorpe jgg@nvidia.com 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 +++ 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;}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?
Oh, nothing, you are right. It just didn't read naturally because hitting the wrong kind of VMA should be an error condition :\
Also follow_pfn checks for this same conditionat already too, so this isn't really stopping anything bad from happening. -Daniel