bpf: sockmap: Enable map_update_elem from bpf_iter

Allow passing a pointer to a BTF struct sock_common* when updating
a sockmap or sockhash. Since BTF pointers can fault and therefore be
NULL at runtime we need to add an additional !sk check to
sock_map_update_elem. Since we may be passed a request or timewait
socket we also need to check sk_fullsock. Doing this allows calling
map_update_elem on sockmap from bpf_iter context, which uses
BTF pointers.
Signed-off-by: Lorenz Bauer <lmb@cloudflare.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Link: https://lore.kernel.org/bpf/20200928090805.23343-2-lmb@cloudflare.com

kernel/bpf/verifier.c

@@ -3943,7 +3943,7 @@ static int resolve_map_arg_type(struct bpf_verifier_env *env,
 	case BPF_MAP_TYPE_SOCKMAP:
 	case BPF_MAP_TYPE_SOCKHASH:
 		if (*arg_type == ARG_PTR_TO_MAP_VALUE) {
-			*arg_type = ARG_PTR_TO_SOCKET;
+			*arg_type = ARG_PTR_TO_BTF_ID_SOCK_COMMON;
 		} else {
 			verbose(env, "invalid arg_type for sockmap/sockhash\n");
 			return -EINVAL;

net/core/sock_map.c

@@ -610,6 +610,9 @@ static int sock_map_update_elem(struct bpf_map *map, void *key,
 	struct sock *sk = (struct sock *)value;
 	int ret;
 
+	if (unlikely(!sk || !sk_fullsock(sk)))
+		return -EINVAL;
+
 	if (!sock_map_sk_is_suitable(sk))
 		return -EOPNOTSUPP;