On Mon, Oct 5, 2020 at 7:58 PM Jason Gunthorpe <jgg@xxxxxxxxxx> 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@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 > > > +++ 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? > > 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 -- Daniel Vetter Software Engineer, Intel Corporation http://blog.ffwll.ch _______________________________________________ dri-devel mailing list dri-devel@xxxxxxxxxxxxxxxxxxxxx https://lists.freedesktop.org/mailman/listinfo/dri-devel