[PATCH 1/1] uffd: wp: clear VM_UFFD_MISSING or VM_UFFD_WP during userfaultfd_register()

[Andrea Arcangeli]

If the registration is repeated without VM_UFFD_MISSING or VM_UFFD_WP
they need to be cleared. Currently setting UFFDIO_REGISTER_MODE_WP
returns -EINVAL, so this patch is a noop until the
UFFDIO_REGISTER_MODE_WP support is applied.

Reported-by: Wei Yang <richardw.yang@xxxxxxxxxxxxxxx>
Signed-off-by: Andrea Arcangeli <aarcange@xxxxxxxxxx>
---
 fs/userfaultfd.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/fs/userfaultfd.c b/fs/userfaultfd.c
index fe6d804a38dc..97596bb65dd5 100644
--- a/fs/userfaultfd.c
+++ b/fs/userfaultfd.c
@@ -1458,7 +1458,8 @@ static int userfaultfd_register(struct userfaultfd_ctx *ctx,
 			start = vma->vm_start;
 		vma_end = min(end, vma->vm_end);
 
-		new_flags = (vma->vm_flags & ~vm_flags) | vm_flags;
+		new_flags = (vma->vm_flags &
+			     ~(VM_UFFD_MISSING|VM_UFFD_WP)) | vm_flags;
 		prev = vma_merge(mm, prev, start, vma_end, new_flags,
 				 vma->anon_vma, vma->vm_file, vma->vm_pgoff,
 				 vma_policy(vma),