[PATCH bpf] bpf: harden flags check in cgroup_storage_update_elem()

[Roman Gushchin]

cgroup_storage_update_elem() shouldn't accept any flags
argument values except BPF_ANY and BPF_EXIST to guarantee
the backward compatibility, had a new flag value been added.

Fixes: de9cbbaadba5 ("bpf: introduce cgroup storage maps")
Signed-off-by: Roman Gushchin <guro@xxxxxx>
Cc: Alexei Starovoitov <ast@xxxxxxxxxx>
Cc: Daniel Borkmann <daniel@xxxxxxxxxxxxx>
---
 kernel/bpf/local_storage.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/bpf/local_storage.c b/kernel/bpf/local_storage.c
index f8746e6a9a35..2a7680106320 100644
--- a/kernel/bpf/local_storage.c
+++ b/kernel/bpf/local_storage.c
@@ -130,7 +130,7 @@ static int cgroup_storage_update_elem(struct bpf_map *map, void *_key,
 	struct bpf_cgroup_storage *storage;
 	struct bpf_storage_buffer *new;
 
-	if (flags & BPF_NOEXIST)
+	if (flags != BPF_ANY && flags != BPF_EXIST)
 		return -EINVAL;
 
 	storage = cgroup_storage_lookup((struct bpf_cgroup_storage_map *)map,
-- 
2.17.1