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 <kafai@fb.com>
Signed-off-by: Stanislav Fomichev <sdf@google.com>
Link: https://lore.kernel.org/r/20220628174314.1216643-7-sdf@google.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

1 files changed, 38 insertions, 0 deletions

diff --git a/kernel/bpf/bpf_lsm.c b/kernel/bpf/bpf_lsm.c
index 83aa431dd52e..d469b7f3deef 100644
--- a/kernel/bpf/bpf_lsm.c
+++ b/kernel/bpf/bpf_lsm.c
@@ -45,6 +45,24 @@ BTF_ID(func, bpf_lsm_sk_alloc_security)
 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)
 {
@@ -201,6 +219,26 @@ bpf_lsm_func_proto(enum bpf_func_id func_id, const struct bpf_prog *prog)
 	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);
 	}