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From:   Yisheng Xie <xieyisheng1@huawei.com>
Subject: [PATCH] mm/mempolicy: Avoid use uninitialized preferred_node
To:     Alexander Potapenko <glider@google.com>,
        <akpm@linux-foundation.org>
References: <CAG_fn=VW5tfzT6cHJd+jF=t3WO6XS3HqSF_TYnKdycX_M_48vw@mail.gmail.com>
CC:     Linux Memory Management List <linux-mm@kvack.org>,
        Dmitriy Vyukov <dvyukov@google.com>, <vbabka@suse.cz>,
        "mhocko@suse.com" <mhocko@suse.com>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
Message-ID: <4ebee1c2-57f6-bcb8-0e2d-1833d1ee0bb7@huawei.com>
Date:   Fri, 9 Mar 2018 13:21:08 +0800
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Alexander reported an use of uninitialized memory in __mpol_equal(),
which is caused by incorrect use of preferred_node.

When mempolicy in mode MPOL_PREFERRED with flags MPOL_F_LOCAL, it use
numa_node_id() instead of preferred_node, however, __mpol_equeue() use
preferred_node without check whether it is MPOL_F_LOCAL or not.

Reported-by: Alexander Potapenko <glider@google.com>
Signed-off-by: Yisheng Xie <xieyisheng1@huawei.com>
---
 mm/mempolicy.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/mm/mempolicy.c b/mm/mempolicy.c
index d879f1d..641545e 100644
--- a/mm/mempolicy.c
+++ b/mm/mempolicy.c
@@ -2124,6 +2124,9 @@ bool __mpol_equal(struct mempolicy *a, struct mempolicy *b)
 	case MPOL_INTERLEAVE:
 		return !!nodes_equal(a->v.nodes, b->v.nodes);
 	case MPOL_PREFERRED:
+		/* a's flags is the same as b's */
+		if (a->flags & MPOL_F_LOCAL)
+			return true;
 		return a->v.preferred_node == b->v.preferred_node;
 	default:
 		BUG();
-- 
1.8.3.1