6.8-stable review patch. If anyone has any objections, please let me know.
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From: Peter Xu peterx@redhat.com
commit c88033efe9a391e72ba6b5df4b01d6e628f4e734 upstream.
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 david@redhat.com Link: https://lkml.kernel.org/r/20240422133311.2987675-1-peterx@redhat.com Reported-by: syzbot+d8426b591c36b21c750e@syzkaller.appspotmail.com Signed-off-by: Peter Xu peterx@redhat.com Reviewed-by: David Hildenbrand david@redhat.com Cc: Nadav Amit nadav.amit@gmail.com Cc: stable@vger.kernel.org Signed-off-by: Andrew Morton akpm@linux-foundation.org Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- fs/userfaultfd.c | 4 ++++ 1 file changed, 4 insertions(+)
--- a/fs/userfaultfd.c +++ b/fs/userfaultfd.c @@ -925,6 +925,10 @@ static int userfaultfd_release(struct in 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,