[PATCH] fs/userfaultfd: Fix vma iteration in mas_for_each() loop

[Liam Howlett]

The maple tree state becomes stale when the tree is altered and requires
the iteration to be paused with mas_pause().  This forces the next
iteration to start from the top of tree for the next entry.

Reported-by: syzbot+68771c0e74f7bb7804e5@xxxxxxxxxxxxxxxxxxxxxxxxx
Fixes: d3ccd17e7c96 ("mm: start tracking VMAs with maple tree")
Signed-off-by: Liam R. Howlett <Liam.Howlett@xxxxxxxxxx>
---
 fs/userfaultfd.c | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/fs/userfaultfd.c b/fs/userfaultfd.c
index d18500633ebe..d398f6bf6d74 100644
--- a/fs/userfaultfd.c
+++ b/fs/userfaultfd.c
@@ -886,10 +886,13 @@ static int userfaultfd_release(struct inode *inode, struct file *file)
 				 vma->vm_file, vma->vm_pgoff,
 				 vma_policy(vma),
 				 NULL_VM_UFFD_CTX, anon_vma_name(vma));
-		if (prev)
+		if (prev) {
+			mas_pause(&mas);
 			vma = prev;
-		else
+		} else {
 			prev = vma;
+		}
+
 		vma->vm_flags = new_flags;
 		vma->vm_userfaultfd_ctx = NULL_VM_UFFD_CTX;
 	}
-- 
2.35.1