netdev - [PATCH bpf-next v8 1/4] bpf: Add update_socket

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Message-Id: <120b307aacd1791fac016d33e112069ffb7db21a.1691047403.git.geliang.tang@suse.com>
Date: Thu,  3 Aug 2023 15:30:39 +0800
From: Geliang Tang <geliang.tang@...e.com>
To: Alexei Starovoitov <ast@...nel.org>,
	Daniel Borkmann <daniel@...earbox.net>,
	Andrii Nakryiko <andrii@...nel.org>,
	Martin KaFai Lau <martin.lau@...ux.dev>,
	Song Liu <song@...nel.org>,
	Yonghong Song <yhs@...com>,
	John Fastabend <john.fastabend@...il.com>,
	KP Singh <kpsingh@...nel.org>,
	Stanislav Fomichev <sdf@...gle.com>,
	Hao Luo <haoluo@...gle.com>,
	Jiri Olsa <jolsa@...nel.org>,
	Florent Revest <revest@...omium.org>,
	Brendan Jackman <jackmanb@...omium.org>,
	Matthieu Baerts <matthieu.baerts@...sares.net>,
	Mat Martineau <martineau@...nel.org>,
	"David S. Miller" <davem@...emloft.net>,
	Eric Dumazet <edumazet@...gle.com>,
	Jakub Kicinski <kuba@...nel.org>,
	Paolo Abeni <pabeni@...hat.com>,
	John Johansen <john.johansen@...onical.com>,
	Paul Moore <paul@...l-moore.com>,
	James Morris <jmorris@...ei.org>,
	"Serge E. Hallyn" <serge@...lyn.com>,
	Stephen Smalley <stephen.smalley.work@...il.com>,
	Eric Paris <eparis@...isplace.org>,
	Mykola Lysenko <mykolal@...com>,
	Shuah Khan <shuah@...nel.org>
Cc: Geliang Tang <geliang.tang@...e.com>,
	bpf@...r.kernel.org,
	netdev@...r.kernel.org,
	mptcp@...ts.linux.dev,
	apparmor@...ts.ubuntu.com,
	linux-security-module@...r.kernel.org,
	selinux@...r.kernel.org,
	linux-kselftest@...r.kernel.org
Subject: [PATCH bpf-next v8 1/4] bpf: Add update_socket_protocol hook

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().

Signed-off-by: Geliang Tang <geliang.tang@...e.com>
---
 net/mptcp/bpf.c | 17 +++++++++++++++++
 net/socket.c    | 25 +++++++++++++++++++++++++
 2 files changed, 42 insertions(+)

diff --git a/net/mptcp/bpf.c b/net/mptcp/bpf.c
index 5a0a84ad94af..c43aee31014d 100644
--- a/net/mptcp/bpf.c
+++ b/net/mptcp/bpf.c
@@ -12,6 +12,23 @@
 #include <linux/bpf.h>
 #include "protocol.h"
 
+#ifdef CONFIG_BPF_JIT
+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);
+#endif /* CONFIG_BPF_JIT */
+
 struct mptcp_sock *bpf_mptcp_sock_from_subflow(struct sock *sk)
 {
 	if (sk && sk_fullsock(sk) && sk->sk_protocol == IPPROTO_TCP && sk_is_mptcp(sk))
diff --git a/net/socket.c b/net/socket.c
index 2b0e54b2405c..586a437d7a5e 100644
--- a/net/socket.c
+++ b/net/socket.c
@@ -1644,11 +1644,36 @@ 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