linux-kernel - [PATCH] userfaultfd/hugetlbfs: Fix minor fault page leak

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Message-Id: <20210322175132.36659-1-peterx@redhat.com>
Date:   Mon, 22 Mar 2021 13:51:32 -0400
From:   Peter Xu <peterx@...hat.com>
To:     linux-mm@...ck.org, linux-kernel@...r.kernel.org
Cc:     Andrew Morton <akpm@...ux-foundation.org>, peterx@...hat.com,
        Axel Rasmussen <axelrasmussen@...gle.com>,
        Andrea Arcangeli <aarcange@...hat.com>,
        Mike Kravetz <mike.kravetz@...cle.com>,
        Mike Rapoport <rppt@...ux.vnet.ibm.com>
Subject: [PATCH] userfaultfd/hugetlbfs: Fix minor fault page leak

When uffd-minor enabled, we need to put the page cache before handling the
userfault in hugetlb_no_page(), otherwise the page refcount got leaked.

This can be reproduced by running userfaultfd selftest with hugetlb_shared
mode, then cat /proc/meminfo.

Cc: Axel Rasmussen <axelrasmussen@...gle.com>
Cc: Andrea Arcangeli <aarcange@...hat.com>
Cc: Mike Kravetz <mike.kravetz@...cle.com>
Cc: Mike Rapoport <rppt@...ux.vnet.ibm.com>
Cc: Andrew Morton <akpm@...ux-foundation.org>
Fixes: f2bf15fb0969 ("userfaultfd: add minor fault registration mode")
Signed-off-by: Peter Xu <peterx@...hat.com>
---
 mm/hugetlb.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index 408dbc08298a..56b78a206913 100644
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -4449,6 +4449,7 @@ static vm_fault_t hugetlb_no_page(struct mm_struct *mm,
 		/* Check for page in userfault range. */
 		if (userfaultfd_minor(vma)) {
 			unlock_page(page);
+			put_page(page);
 			ret = hugetlb_handle_userfault(vma, mapping, idx,
 						       flags, haddr,
 						       VM_UFFD_MINOR);
-- 
2.26.2