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>

3 files changed, 93 insertions, 7 deletions

diff --git a/include/linux/bpf.h b/include/linux/bpf.h
index 5d2afa55c7c3..2b21f2a3452f 100644
--- a/include/linux/bpf.h
+++ b/include/linux/bpf.h
@@ -2386,6 +2386,8 @@ extern const struct bpf_func_proto bpf_for_each_map_elem_proto;
 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;
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);
 	}
diff --git a/net/core/filter.c b/net/core/filter.c
index 151aa4756bd6..c6941ab0eb52 100644
--- a/net/core/filter.c
+++ b/net/core/filter.c
@@ -5012,8 +5012,8 @@ static const struct bpf_func_proto bpf_get_socket_uid_proto = {
 	.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;
@@ -5024,8 +5024,6 @@ static int _bpf_setsockopt(struct sock *sk, int level, int optname,
 	if (!sk_fullsock(sk))
 		return -EINVAL;
 
-	sock_owned_by_me(sk);
-
 	if (level == SOL_SOCKET) {
 		if (optlen != sizeof(int) && optname != SO_BINDTODEVICE)
 			return -EINVAL;
@@ -5258,14 +5256,20 @@ static int _bpf_setsockopt(struct sock *sk, int level, int optname,
 	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))
 			goto err_clear;
@@ -5360,6 +5364,14 @@ err_clear:
 	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)
 {
@@ -5400,6 +5412,40 @@ const struct bpf_func_proto bpf_sk_getsockopt_proto = {
 	.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,
+	.arg2_type	= ARG_ANYTHING,
+	.arg3_type	= ARG_ANYTHING,
+	.arg4_type	= ARG_PTR_TO_UNINIT_MEM,
+	.arg5_type	= ARG_CONST_SIZE,
+};
+
 BPF_CALL_5(bpf_sock_addr_setsockopt, struct bpf_sock_addr_kern *, ctx,
 	   int, level, int, optname, char *, optval, int, optlen)
 {