[PATCH bpf-next v11 1/5] bpf: Add update_socket_protocol hook

Geliang Tang
2023-08-04T05:07:42Z

Add a hook named update_socket_protocol in __sys_socket(), for bpf
progs to attach to and update socket protocol. One user case is to
force legacy TCP apps to create and use MPTCP sockets instead of
TCP ones.

Define a mod_ret set named bpf_mptcp_fmodret_ids, add the hook
update_socket_protocol into this set, and register it in
bpf_mptcp_kfunc_init().

Closes: https://github.com/multipath-tcp/mptcp_net-next/issues/79
Acked-by: Matthieu Baerts <matthieu.baerts@tessares.net>
Acked-by: Yonghong Song <yonghong.song@linux.dev>
Signed-off-by: Geliang Tang <geliang.tang@suse.com>
---
net/mptcp/bpf.c | 15 +++++++++++++++
net/socket.c | 24 ++++++++++++++++++++++++
2 files changed, 39 insertions(+)

diff --git a/net/mptcp/bpf.c b/net/mptcp/bpf.c
index 5a0a84ad94af..8a16672b94e2 100644
--- a/net/mptcp/bpf.c
+++ b/net/mptcp/bpf.c
@@ -19,3 +19,18 @@ struct mptcp_sock *bpf_mptcp_sock_from_subflow(struct sock *sk)

return NULL;
}
+
+BTF_SET8_START(bpf_mptcp_fmodret_ids)
+BTF_ID_FLAGS(func, update_socket_protocol)
+BTF_SET8_END(bpf_mptcp_fmodret_ids)
+
+static const struct btf_kfunc_id_set bpf_mptcp_fmodret_set = {
+ .owner = THIS_MODULE,
+ .set = &bpf_mptcp_fmodret_ids,
+};
+
+static int __init bpf_mptcp_kfunc_init(void)
+{
+ return register_btf_fmodret_id_set(&bpf_mptcp_fmodret_set);
+}
+late_initcall(bpf_mptcp_kfunc_init);
diff --git a/net/socket.c b/net/socket.c
index 2b0e54b2405c..9f98ced88ac5 100644
--- a/net/socket.c
+++ b/net/socket.c
@@ -1644,11 +1644,35 @@ struct file *__sys_socket_file(int family, int type, int protocol)
return sock_alloc_file(sock, flags, NULL);
}

+/* A hook for bpf progs to attach to and update socket protocol.
+ *
+ * A static noinline declaration here could cause the compiler to
+ * optimize away the function. A global noinline declaration will
+ * keep the definition, but may optimize away the callsite.
+ * Therefore, __weak is needed to ensure that the call is still
+ * emitted, by telling the compiler that we don't know what the
+ * function might eventually be.
+ *
+ * __diag_* below are needed to dismiss the missing prototype warning.
+ */
+
+__diag_push();
+__diag_ignore_all("-Wmissing-prototypes",
+ "kfuncs which will be used in BPF programs");
+
+__weak noinline int update_socket_protocol(int family, int type, int protocol)
+{
+ return protocol;
+}
+
+__diag_pop();
+
int __sys_socket(int family, int type, int protocol)
{
struct socket *sock;
int flags;

+ protocol = update_socket_protocol(family, type, protocol);
sock = __sys_socket_create(family, type, protocol);
if (IS_ERR(sock))
return PTR_ERR(sock);
--
2.35.3