On 12.01.24 02:39, Suren Baghdasaryan wrote:
While testing UFFDIO_MOVE ioctl, syzbot triggered VM_BUG_ON_PAGE caused
by a call to PageAnonExclusive() with a huge_zero_page as a parameter.
UFFDIO_MOVE does not yet handle zeropages and returns EBUSY when one is
encountered. Add an early huge_zero_page check in the PMD move path
to avoid this situation.
Reported-by: syzbot+705209281e36404998f6@xxxxxxxxxxxxxxxxxxxxxxxxx
Fixes: adef440691ba ("userfaultfd: UFFDIO_MOVE uABI")
Signed-off-by: Suren Baghdasaryan <surenb@xxxxxxxxxx>
---
Applies cleanly over linux-next, mm-stable and mm-unstable branches
mm/userfaultfd.c | 6 ++++++
1 file changed, 6 insertions(+)
diff --git a/mm/userfaultfd.c b/mm/userfaultfd.c
index 216ab4c8621f..20e3b0d9cf7e 100644
--- a/mm/userfaultfd.c
+++ b/mm/userfaultfd.c
@@ -1393,6 +1393,12 @@ ssize_t move_pages(struct userfaultfd_ctx *ctx, struct mm_struct *mm,
err = -ENOENT;
break;
}
+ /* Avoid moving zeropages for now */
+ if (is_huge_zero_pmd(*src_pmd)) {
+ spin_unlock(ptl);
+ err = -EBUSY;
+ break;
+ }
As an alternative (and more future proof?) just reject anything that is
not an anon folio as well?
Anyhow, this should handle the issue at hand.
Acked-by: David Hildenbrand <david@xxxxxxxxxx>
--
Cheers,
David / dhildenb
