linux-kernel - [PATCH 4.19 354/425] ksm: fix potential missing rmap_item for stable

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: Windows password security audit tool. GUI, reports in PDF.

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

Message-Id: <20210520092143.043634008@linuxfoundation.org>
Date:   Thu, 20 May 2021 11:22:03 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Miaohe Lin <linmiaohe@...wei.com>,
        Hugh Dickins <hughd@...gle.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Sasha Levin <sashal@...nel.org>
Subject: [PATCH 4.19 354/425] ksm: fix potential missing rmap_item for stable_node

From: Miaohe Lin <linmiaohe@...wei.com>

[ Upstream commit c89a384e2551c692a9fe60d093fd7080f50afc51 ]

When removing rmap_item from stable tree, STABLE_FLAG of rmap_item is
cleared with head reserved.  So the following scenario might happen: For
ksm page with rmap_item1:

cmp_and_merge_page
  stable_node->head = &migrate_nodes;
  remove_rmap_item_from_tree, but head still equal to stable_node;
  try_to_merge_with_ksm_page failed;
  return;

For the same ksm page with rmap_item2, stable node migration succeed this
time.  The stable_node->head does not equal to migrate_nodes now.  For ksm
page with rmap_item1 again:

cmp_and_merge_page
 stable_node->head != &migrate_nodes && rmap_item->head == stable_node
 return;

We would miss the rmap_item for stable_node and might result in failed
rmap_walk_ksm().  Fix this by set rmap_item->head to NULL when rmap_item
is removed from stable tree.

Link: https://lkml.kernel.org/r/20210330140228.45635-5-linmiaohe@huawei.com
Fixes: 4146d2d673e8 ("ksm: make !merge_across_nodes migration safe")
Signed-off-by: Miaohe Lin <linmiaohe@...wei.com>
Cc: Hugh Dickins <hughd@...gle.com>
Signed-off-by: Andrew Morton <akpm@...ux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@...ux-foundation.org>
Signed-off-by: Sasha Levin <sashal@...nel.org>
---
 mm/ksm.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/mm/ksm.c b/mm/ksm.c
index d021bcf94c41..87a541ab1474 100644
--- a/mm/ksm.c
+++ b/mm/ksm.c
@@ -778,6 +778,7 @@ static void remove_rmap_item_from_tree(struct rmap_item *rmap_item)
 		stable_node->rmap_hlist_len--;
 
 		put_anon_vma(rmap_item->anon_vma);
+		rmap_item->head = NULL;
 		rmap_item->address &= PAGE_MASK;
 
 	} else if (rmap_item->address & UNSTABLE_FLAG) {
-- 
2.30.2