linux-kernel - [PATCH v2] hugetlb, userfaultfd: Fix reservation restore on userfaultfd error

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Message-Id: <20211117193825.378528-1-almasrymina@google.com>
Date:   Wed, 17 Nov 2021 11:38:24 -0800
From:   Mina Almasry <almasrymina@...gle.com>
To:     Mike Kravetz <mike.kravetz@...cle.com>,
        Andrew Morton <akpm@...ux-foundation.org>
Cc:     Mina Almasry <almasrymina@...gle.com>, Wei Xu <weixugc@...gle.com>,
        stable@...r.kernel.org, James Houghton <jthoughton@...gle.com>,
        linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: [PATCH v2] hugetlb, userfaultfd: Fix reservation restore on
 userfaultfd error

Currently in the is_continue case in hugetlb_mcopy_atomic_pte(), if we
bail out using "goto out_release_unlock;" in the cases where idx >=
size, or !huge_pte_none(), the code will detect that new_pagecache_page
== false, and so call restore_reserve_on_error().
In this case I see restore_reserve_on_error() delete the reservation,
and the following call to remove_inode_hugepages() will increment
h->resv_hugepages causing a 100% reproducible leak.

We should treat the is_continue case similar to adding a page into the
pagecache and set new_pagecache_page to true, to indicate that there is
no reservation to restore on the error path, and we need not call
restore_reserve_on_error().  Rename new_pagecache_page to
page_in_pagecache to make that clear.

Cc: Wei Xu <weixugc@...gle.com>

Cc: stable@...r.kernel.org

Fixes: c7b1850dfb41 ("hugetlb: don't pass page cache pages to restore_reserve_on_error")
Signed-off-by: Mina Almasry <almasrymina@...gle.com>
Reported-by: James Houghton <jthoughton@...gle.com>


---

Changes in v2:
- Renamed new_pagecache_page to page_in_pagecache
- Removed unnecessary comment after the name update.
- Cc: stable
---
 mm/hugetlb.c | 7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index e09159c957e3..e7ebc4b355cf 100644
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -5734,13 +5734,14 @@ int hugetlb_mcopy_atomic_pte(struct mm_struct *dst_mm,
 	int ret = -ENOMEM;
 	struct page *page;
 	int writable;
-	bool new_pagecache_page = false;
+	bool page_in_pagecache = false;

 	if (is_continue) {
 		ret = -EFAULT;
 		page = find_lock_page(mapping, idx);
 		if (!page)
 			goto out;
+		page_in_pagecache = true;
 	} else if (!*pagep) {
 		/* If a page already exists, then it's UFFDIO_COPY for
 		 * a non-missing case. Return -EEXIST.
@@ -5828,7 +5829,7 @@ int hugetlb_mcopy_atomic_pte(struct mm_struct *dst_mm,
 		ret = huge_add_to_page_cache(page, mapping, idx);
 		if (ret)
 			goto out_release_nounlock;
-		new_pagecache_page = true;
+		page_in_pagecache = true;
 	}

 	ptl = huge_pte_lockptr(h, dst_mm, dst_pte);
@@ -5892,7 +5893,7 @@ int hugetlb_mcopy_atomic_pte(struct mm_struct *dst_mm,
 	if (vm_shared || is_continue)
 		unlock_page(page);
 out_release_nounlock:
-	if (!new_pagecache_page)
+	if (!page_in_pagecache)
 		restore_reserve_on_error(h, dst_vma, dst_addr, page);
 	put_page(page);
 	goto out;
--
2.34.0.rc2.393.gf8c9666880-goog