mm/mempolicy.c: avoid use uninitialized preferred_node

commit 8970a63e965b43288c4f5f40efbc2bbf80de7f16 upstream.

Alexander reported a 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 uses
numa_node_id() instead of preferred_node, however, __mpol_equal() uses
preferred_node without checking whether it is MPOL_F_LOCAL or not.

[akpm@linux-foundation.org: slight comment tweak]
Link: http://lkml.kernel.org/r/4ebee1c2-57f6-bcb8-0e2d-1833d1ee0bb7@huawei.com
Fixes: fc36b8d3d819 ("mempolicy: use MPOL_F_LOCAL to Indicate Preferred Local Policy")
Signed-off-by: Yisheng Xie <xieyisheng1@huawei.com>
Reported-by: Alexander Potapenko <glider@google.com>
Tested-by: Alexander Potapenko <glider@google.com>
Reviewed-by: Andrew Morton <akpm@linux-foundation.org>
Cc: Dmitriy Vyukov <dvyukov@google.com>
Cc: Vlastimil Babka <vbabka@suse.cz>
Cc: Michal Hocko <mhocko@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>

diff --git a/mm/mempolicy.c b/mm/mempolicy.c
index 1ea67ad..b056dc2 100644 (file)
--- a/mm/mempolicy.c
+++ b/mm/mempolicy.c
@@ -2019,6 +2019,9 @@ int __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();