[PATCH] mm: don't allow empty relative nodemask in mpol_relative_nodemask()

[Yury Norov]

Reassigning nodes relative an empty user-provided nodemask is useless,
and triggers divide-by-zero in the function.

Reported-by: Farhad Alemi <farhad.alemi@xxxxxxxxxxxx>
Link: https://lore.kernel.org/all/CA+0ovCgxbZkXa+OU8w3s84R3KNPNxxRfmsNR-udh+afQBbGNmw@xxxxxxxxxxxxxx/
Signed-off-by: Yury Norov <ynorov@xxxxxxxxxx>
---
 mm/mempolicy.c | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/mm/mempolicy.c b/mm/mempolicy.c
index 4e4421b22b59..cd961fa1eb33 100644
--- a/mm/mempolicy.c
+++ b/mm/mempolicy.c
@@ -370,8 +370,13 @@ static inline int mpol_store_user_nodemask(const struct mempolicy *pol)
 static void mpol_relative_nodemask(nodemask_t *ret, const nodemask_t *orig,
 				   const nodemask_t *rel)
 {
+	unsigned int w = nodes_weight(*rel);
 	nodemask_t tmp;
-	nodes_fold(tmp, *orig, nodes_weight(*rel));
+
+	if (w == 0)
+		return -EINVAL;
+
+	nodes_fold(tmp, *orig, w);
 	nodes_onto(*ret, tmp, *rel);
 }
 
-- 
2.51.0