linux-kernel - [PATCH] mm: userfaultfd: fix unexpected change to src_folio when UFFDIO

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Message-Id: <20240222080815.46291-1-zhengqi.arch@bytedance.com>
Date: Thu, 22 Feb 2024 16:08:15 +0800
From: Qi Zheng <zhengqi.arch@...edance.com>
To: akpm@...ux-foundation.org,
	aarcange@...hat.com,
	surenb@...gle.com,
	david@...hat.com
Cc: linux-mm@...ck.org,
	linux-kernel@...r.kernel.org,
	Qi Zheng <zhengqi.arch@...edance.com>
Subject: [PATCH] mm: userfaultfd: fix unexpected change to src_folio when UFFDIO_MOVE fails

After ptep_clear_flush(), if we find that src_folio is pinned we will fail
UFFDIO_MOVE and put src_folio back to src_pte entry, but the change to
src_folio->{mapping,index} is not restored in this process. This is not
what we expected, so fix it.

Fixes: adef440691ba ("userfaultfd: UFFDIO_MOVE uABI")
Signed-off-by: Qi Zheng <zhengqi.arch@...edance.com>
---
 mm/userfaultfd.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/mm/userfaultfd.c b/mm/userfaultfd.c
index 4744d6a96f96..503ea77c81aa 100644
--- a/mm/userfaultfd.c
+++ b/mm/userfaultfd.c
@@ -1008,9 +1008,6 @@ static int move_present_pte(struct mm_struct *mm,
 		goto out;
 	}
 
-	folio_move_anon_rmap(src_folio, dst_vma);
-	WRITE_ONCE(src_folio->index, linear_page_index(dst_vma, dst_addr));
-
 	orig_src_pte = ptep_clear_flush(src_vma, src_addr, src_pte);
 	/* Folio got pinned from under us. Put it back and fail the move. */
 	if (folio_maybe_dma_pinned(src_folio)) {
@@ -1019,6 +1016,9 @@ static int move_present_pte(struct mm_struct *mm,
 		goto out;
 	}
 
+	folio_move_anon_rmap(src_folio, dst_vma);
+	WRITE_ONCE(src_folio->index, linear_page_index(dst_vma, dst_addr));
+
 	orig_dst_pte = mk_pte(&src_folio->page, dst_vma->vm_page_prot);
 	/* Follow mremap() behavior and treat the entry dirty after the move */
 	orig_dst_pte = pte_mkwrite(pte_mkdirty(orig_dst_pte), dst_vma);
-- 
2.30.2