bpf, sockmap: Let all kernel-land lookup values in SOCKMAP/SOCKHASH

Don't require the kernel code, like BPF helpers, that needs access to
SOCK{MAP,HASH} map contents to live in net/core/sock_map.c. Expose the
lookup operation to all kernel-land.

Lookup from BPF context is not whitelisted yet. While syscalls have a
dedicated lookup handler.
Signed-off-by: Jakub Sitnicki <jakub@cloudflare.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: John Fastabend <john.fastabend@gmail.com>
Link: https://lore.kernel.org/bpf/20200218171023.844439-8-jakub@cloudflare.com

net/core/sock_map.c

@@ -301,7 +301,7 @@ static struct sock *__sock_map_lookup_elem(struct bpf_map *map, u32 key)
 
 static void *sock_map_lookup(struct bpf_map *map, void *key)
 {
-	return ERR_PTR(-EOPNOTSUPP);
+	return __sock_map_lookup_elem(map, *(u32 *)key);
 }
 
 static void *sock_map_lookup_sys(struct bpf_map *map, void *key)
@@ -991,6 +991,11 @@ static void *sock_hash_lookup_sys(struct bpf_map *map, void *key)
 	return &sk->sk_cookie;
 }
 
+static void *sock_hash_lookup(struct bpf_map *map, void *key)
+{
+	return __sock_hash_lookup_elem(map, key);
+}
+
 static void sock_hash_release_progs(struct bpf_map *map)
 {
 	psock_progs_drop(&container_of(map, struct bpf_htab, map)->progs);
@@ -1079,7 +1084,7 @@ const struct bpf_map_ops sock_hash_ops = {
 	.map_get_next_key	= sock_hash_get_next_key,
 	.map_update_elem	= sock_hash_update_elem,
 	.map_delete_elem	= sock_hash_delete_elem,
-	.map_lookup_elem	= sock_map_lookup,
+	.map_lookup_elem	= sock_hash_lookup,
 	.map_lookup_elem_sys_only = sock_hash_lookup_sys,
 	.map_release_uref	= sock_hash_release_progs,
 	.map_check_btf		= map_check_no_btf,