linux-kernel - [PATCH 3/3] mm/hugetlb: use get_page_unless_zero() in hugetlb

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite for Android: free password hash cracker in your pocket

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-Id: <1406570911-28133-3-git-send-email-n-horiguchi@ah.jp.nec.com>
Date:	Mon, 28 Jul 2014 14:08:31 -0400
From:	Naoya Horiguchi <n-horiguchi@...jp.nec.com>
To:	Andrew Morton <akpm@...ux-foundation.org>,
	Hugh Dickins <hughd@...gle.com>
Cc:	linux-mm@...ck.org, linux-kernel@...r.kernel.org,
	Naoya Horiguchi <nao.horiguchi@...il.com>
Subject: [PATCH 3/3] mm/hugetlb: use get_page_unless_zero() in hugetlb_fault()

After fixing the race in follow_page(FOLL_GET) for hugepages, I start to
observe the BUG of "get_page() on refcount 0 page" in hugetlb_fault() in
the same test.

I'm not exactly sure about how this race is triggered, but hugetlb_fault()
calls pte_page() and get_page() outside page table lock, so it's not safe.
This patch checks the refcount of the gotten page, and aborts the page fault
if the refcount is 0, expecting to retry.

Signed-off-by: Naoya Horiguchi <n-horiguchi@...jp.nec.com>
Cc: <stable@...r.kernel.org>  # [3.12+]
---
 mm/hugetlb.c | 12 ++++++------
 1 file changed, 6 insertions(+), 6 deletions(-)

diff --git mmotm-2014-07-22-15-58.orig/mm/hugetlb.c mmotm-2014-07-22-15-58/mm/hugetlb.c
index 6793914b6aac..86e7341aad77 100644
--- mmotm-2014-07-22-15-58.orig/mm/hugetlb.c
+++ mmotm-2014-07-22-15-58/mm/hugetlb.c
@@ -3189,7 +3189,8 @@ int hugetlb_fault(struct mm_struct *mm, struct vm_area_struct *vma,
 	 * so no worry about deadlock.
 	 */
 	page = pte_page(entry);
-	get_page(page);
+	if (!get_page_unless_zero(page))
+		goto out_put_pagecache;
 	if (page != pagecache_page)
 		lock_page(page);
 
@@ -3215,15 +3216,14 @@ int hugetlb_fault(struct mm_struct *mm, struct vm_area_struct *vma,
 
 out_ptl:
 	spin_unlock(ptl);
-
+	if (page != pagecache_page)
+		unlock_page(page);
+	put_page(page);
+out_put_pagecache:
 	if (pagecache_page) {
 		unlock_page(pagecache_page);
 		put_page(pagecache_page);
 	}
-	if (page != pagecache_page)
-		unlock_page(page);
-	put_page(page);
-
 out_mutex:
 	mutex_unlock(&htlb_fault_mutex_table[hash]);
 	return ret;
-- 
1.9.3

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/