[PATCH] mm/mempolicy: Avoid use uninitialized preferred_node

[Yisheng Xie]

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@xxxxxxxxxx>
Signed-off-by: Yisheng Xie <xieyisheng1@xxxxxxxxxx>
---
 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