userfaultfd: shmem/hugetlbfs: only allow to register VM_MAYWRITE vmas
After the VMA to register the uffd onto is found, check that it has
VM_MAYWRITE set before allowing registration. This way we inherit all
common code checks before allowing to fill file holes in shmem and
hugetlbfs with UFFDIO_COPY.
The userfaultfd memory model is not applicable for readonly files unless
it's a MAP_PRIVATE.
Link: http://lkml.kernel.org/r/20181126173452.26955-4-aarcange@redhat.com
Fixes: ff62a3421044 ("hugetlb: implement memfd sealing")
Signed-off-by: Andrea Arcangeli <aarcange@redhat.com>
Reviewed-by: Mike Rapoport <rppt@linux.ibm.com>
Reviewed-by: Hugh Dickins <hughd@google.com>
Reported-by: Jann Horn <jannh@google.com>
Fixes: 4c27fe4c4c84 ("userfaultfd: shmem: add shmem_mcopy_atomic_pte for userfaultfd support")
Cc: <stable@vger.kernel.org>
Cc: "Dr. David Alan Gilbert" <dgilbert@redhat.com>
Cc: Mike Kravetz <mike.kravetz@oracle.com>
Cc: Peter Xu <peterx@redhat.com>
Cc: stable@vger.kernel.org
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/mm/userfaultfd.c b/mm/userfaultfd.c
index 471b645..43cf314 100644
--- a/mm/userfaultfd.c
+++ b/mm/userfaultfd.c
@@ -205,8 +205,9 @@
if (!dst_vma || !is_vm_hugetlb_page(dst_vma))
goto out_unlock;
/*
- * Only allow __mcopy_atomic_hugetlb on userfaultfd
- * registered ranges.
+ * Check the vma is registered in uffd, this is
+ * required to enforce the VM_MAYWRITE check done at
+ * uffd registration time.
*/
if (!dst_vma->vm_userfaultfd_ctx.ctx)
goto out_unlock;
@@ -459,13 +460,9 @@
if (!dst_vma)
goto out_unlock;
/*
- * Be strict and only allow __mcopy_atomic on userfaultfd
- * registered ranges to prevent userland errors going
- * unnoticed. As far as the VM consistency is concerned, it
- * would be perfectly safe to remove this check, but there's
- * no useful usage for __mcopy_atomic ouside of userfaultfd
- * registered ranges. This is after all why these are ioctls
- * belonging to the userfaultfd and not syscalls.
+ * Check the vma is registered in uffd, this is required to
+ * enforce the VM_MAYWRITE check done at uffd registration
+ * time.
*/
if (!dst_vma->vm_userfaultfd_ctx.ctx)
goto out_unlock;