From c88033efe9a391e72ba6b5df4b01d6e628f4e734 Mon Sep 17 00:00:00 2001 From: Peter Xu Date: Mon, 22 Apr 2024 09:33:11 -0400 Subject: [PATCH] mm/userfaultfd: reset ptes when close() for wr-protected ones Userfaultfd unregister includes a step to remove wr-protect bits from all the relevant pgtable entries, but that only covered an explicit UFFDIO_UNREGISTER ioctl, not a close() on the userfaultfd itself. Cover that too. This fixes a WARN trace. The only user visible side effect is the user can observe leftover wr-protect bits even if the user close()ed on an userfaultfd when releasing the last reference of it. However hopefully that should be harmless, and nothing bad should happen even if so. This change is now more important after the recent page-table-check patch we merged in mm-unstable (446dd9ad37d0 ("mm/page_table_check: support userfault wr-protect entries")), as we'll do sanity check on uffd-wp bits without vma context. So it's better if we can 100% guarantee no uffd-wp bit leftovers, to make sure each report will be valid. Link: https://lore.kernel.org/all/000000000000ca4df20616a0fe16@google.com/ Fixes: f369b07c8614 ("mm/uffd: reset write protection when unregister with wp-mode") Analyzed-by: David Hildenbrand Link: https://lkml.kernel.org/r/20240422133311.2987675-1-peterx@redhat.com Reported-by: syzbot+d8426b591c36b21c750e@syzkaller.appspotmail.com Signed-off-by: Peter Xu Reviewed-by: David Hildenbrand Cc: Nadav Amit Cc: Signed-off-by: Andrew Morton --- fs/userfaultfd.c | 4 ++++ 1 file changed, 4 insertions(+) diff --git a/fs/userfaultfd.c b/fs/userfaultfd.c index 60dcfafdc11a..292f5fd50104 100644 --- a/fs/userfaultfd.c +++ b/fs/userfaultfd.c @@ -895,6 +895,10 @@ static int userfaultfd_release(struct inode *inode, struct file *file) prev = vma; continue; } + /* Reset ptes for the whole vma range if wr-protected */ + if (userfaultfd_wp(vma)) + uffd_wp_range(vma, vma->vm_start, + vma->vm_end - vma->vm_start, false); new_flags = vma->vm_flags & ~__VM_UFFD_FLAGS; vma = vma_modify_flags_uffd(&vmi, prev, vma, vma->vm_start, vma->vm_end, new_flags,