bpf: harden flags check in cgroup_storage_update_elem()

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@fb.com>
Reported-by: Daniel Borkmann <daniel@iogearbox.net>
Cc: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>

diff --git a/kernel/bpf/local_storage.c b/kernel/bpf/local_storage.c
index 22ad967d1e5f14b9bafd41a99117b97700e041f6..94126cbffc880f76d50ede6b21940348890343f7 100644 (file)
--- a/kernel/bpf/local_storage.c
+++ b/kernel/bpf/local_storage.c
@@ -129,7 +129,7 @@ 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,