bpf: expose bpf_{g,s}etsockopt to lsm cgroup

I don't see how to make it nice without introducing btf id lists
for the hooks where these helpers are allowed. Some LSM hooks
work on the locked sockets, some are triggering early and
don't grab any locks, so have two lists for now:

1. LSM hooks which trigger under socket lock - minority of the hooks,
but ideal case for us, we can expose existing BTF-based helpers
2. LSM hooks which trigger without socket lock, but they trigger
early in the socket creation path where it should be safe to
do setsockopt without any locks
3. The rest are prohibited. I'm thinking that this use-case might
be a good gateway to sleeping lsm cgroup hooks in the future.
We can either expose lock/unlock operations (and add tracking
to the verifier) or have another set of bpf_setsockopt
wrapper that grab the locks and might sleep.

Reviewed-by: Martin KaFai Lau <[e-mail]>
Signed-off-by: Stanislav Fomichev <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Alexei Starovoitov <[e-mail]>

include/linux/bpf.h

···
 extern const struct bpf_func_proto bpf_btf_find_by_name_kind_proto;
 extern const struct bpf_func_proto bpf_sk_setsockopt_proto;
 extern const struct bpf_func_proto bpf_sk_getsockopt_proto;
+extern const struct bpf_func_proto bpf_unlocked_sk_setsockopt_proto;
+extern const struct bpf_func_proto bpf_unlocked_sk_getsockopt_proto;
 extern const struct bpf_func_proto bpf_find_vma_proto;
 extern const struct bpf_func_proto bpf_loop_proto;
 extern const struct bpf_func_proto bpf_copy_from_user_task_proto;

kernel/bpf/bpf_lsm.c

···
 BTF_ID(func, bpf_lsm_sk_free_security)
 BTF_SET_END(bpf_lsm_current_hooks)
 
+/* List of LSM hooks that trigger while the socket is properly locked.
+ */
+BTF_SET_START(bpf_lsm_locked_sockopt_hooks)
+BTF_ID(func, bpf_lsm_socket_sock_rcv_skb)
+BTF_ID(func, bpf_lsm_sock_graft)
+BTF_ID(func, bpf_lsm_inet_csk_clone)
+BTF_ID(func, bpf_lsm_inet_conn_established)
+BTF_SET_END(bpf_lsm_locked_sockopt_hooks)
+
+/* List of LSM hooks that trigger while the socket is _not_ locked,
+ * but it's ok to call bpf_{g,s}etsockopt because the socket is still
+ * in the early init phase.
+ */
+BTF_SET_START(bpf_lsm_unlocked_sockopt_hooks)
+BTF_ID(func, bpf_lsm_socket_post_create)
+BTF_ID(func, bpf_lsm_socket_socketpair)
+BTF_SET_END(bpf_lsm_unlocked_sockopt_hooks)
+
 void bpf_lsm_find_cgroup_shim(const struct bpf_prog *prog,
 			     bpf_func_t *bpf_func)
 {
···
 	case BPF_FUNC_get_retval:
 		return prog->expected_attach_type == BPF_LSM_CGROUP ?
 			&bpf_get_retval_proto : NULL;
+	case BPF_FUNC_setsockopt:
+		if (prog->expected_attach_type != BPF_LSM_CGROUP)
+			return NULL;
+		if (btf_id_set_contains(&bpf_lsm_locked_sockopt_hooks,
+					prog->aux->attach_btf_id))
+			return &bpf_sk_setsockopt_proto;
+		if (btf_id_set_contains(&bpf_lsm_unlocked_sockopt_hooks,
+					prog->aux->attach_btf_id))
+			return &bpf_unlocked_sk_setsockopt_proto;
+		return NULL;
+	case BPF_FUNC_getsockopt:
+		if (prog->expected_attach_type != BPF_LSM_CGROUP)
+			return NULL;
+		if (btf_id_set_contains(&bpf_lsm_locked_sockopt_hooks,
+					prog->aux->attach_btf_id))
+			return &bpf_sk_getsockopt_proto;
+		if (btf_id_set_contains(&bpf_lsm_unlocked_sockopt_hooks,
+					prog->aux->attach_btf_id))
+			return &bpf_unlocked_sk_getsockopt_proto;
+		return NULL;
 	default:
 		return tracing_prog_func_proto(func_id, prog);
 	}

net/core/filter.c

···
 	.arg1_type      = ARG_PTR_TO_CTX,
 };
 
-static int _bpf_setsockopt(struct sock *sk, int level, int optname,
-			   char *optval, int optlen)
+static int __bpf_setsockopt(struct sock *sk, int level, int optname,
+			    char *optval, int optlen)
 {
 	char devname[IFNAMSIZ];
 	int val, valbool;
···
 
 	if (!sk_fullsock(sk))
 		return -EINVAL;
-
-	sock_owned_by_me(sk);
 
 	if (level == SOL_SOCKET) {
 		if (optlen != sizeof(int) && optname != SO_BINDTODEVICE)
···
 	return ret;
 }
 
-static int _bpf_getsockopt(struct sock *sk, int level, int optname,
+static int _bpf_setsockopt(struct sock *sk, int level, int optname,
 			   char *optval, int optlen)
+{
+	if (sk_fullsock(sk))
+		sock_owned_by_me(sk);
+	return __bpf_setsockopt(sk, level, optname, optval, optlen);
+}
+
+static int __bpf_getsockopt(struct sock *sk, int level, int optname,
+			    char *optval, int optlen)
 {
 	if (!sk_fullsock(sk))
 		goto err_clear;
-
-	sock_owned_by_me(sk);
 
 	if (level == SOL_SOCKET) {
 		if (optlen != sizeof(int))
···
 	return -EINVAL;
 }
 
+static int _bpf_getsockopt(struct sock *sk, int level, int optname,
+			   char *optval, int optlen)
+{
+	if (sk_fullsock(sk))
+		sock_owned_by_me(sk);
+	return __bpf_getsockopt(sk, level, optname, optval, optlen);
+}
+
 BPF_CALL_5(bpf_sk_setsockopt, struct sock *, sk, int, level,
 	   int, optname, char *, optval, int, optlen)
 {
···
 
 const struct bpf_func_proto bpf_sk_getsockopt_proto = {
 	.func		= bpf_sk_getsockopt,
+	.gpl_only	= false,
+	.ret_type	= RET_INTEGER,
+	.arg1_type	= ARG_PTR_TO_BTF_ID_SOCK_COMMON,
+	.arg2_type	= ARG_ANYTHING,
+	.arg3_type	= ARG_ANYTHING,
+	.arg4_type	= ARG_PTR_TO_UNINIT_MEM,
+	.arg5_type	= ARG_CONST_SIZE,
+};
+
+BPF_CALL_5(bpf_unlocked_sk_setsockopt, struct sock *, sk, int, level,
+	   int, optname, char *, optval, int, optlen)
+{
+	return __bpf_setsockopt(sk, level, optname, optval, optlen);
+}
+
+const struct bpf_func_proto bpf_unlocked_sk_setsockopt_proto = {
+	.func		= bpf_unlocked_sk_setsockopt,
+	.gpl_only	= false,
+	.ret_type	= RET_INTEGER,
+	.arg1_type	= ARG_PTR_TO_BTF_ID_SOCK_COMMON,
+	.arg2_type	= ARG_ANYTHING,
+	.arg3_type	= ARG_ANYTHING,
+	.arg4_type	= ARG_PTR_TO_MEM | MEM_RDONLY,
+	.arg5_type	= ARG_CONST_SIZE,
+};
+
+BPF_CALL_5(bpf_unlocked_sk_getsockopt, struct sock *, sk, int, level,
+	   int, optname, char *, optval, int, optlen)
+{
+	return __bpf_getsockopt(sk, level, optname, optval, optlen);
+}
+
+const struct bpf_func_proto bpf_unlocked_sk_getsockopt_proto = {
+	.func		= bpf_unlocked_sk_getsockopt,
 	.gpl_only	= false,
 	.ret_type	= RET_INTEGER,
 	.arg1_type	= ARG_PTR_TO_BTF_ID_SOCK_COMMON,