Re: [PATCH 2/2] mm/frame-vec: use FOLL_LONGTERM

[Jason Gunthorpe]

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));
 out:
 	if (locked)
-- 
2.28.0