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 fmod_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>
Link: https://lore.kernel.org/r/ac84be00f97072a46f8a72b4e2be46cbb7fa5053.1692147782.git.geliang.tang@suse.com
Signed-off-by: Martin KaFai Lau <martin.lau@kernel.org>
diff --git a/net/socket.c b/net/socket.c
index 5d4e375..fdb5233 100644
--- a/net/socket.c
+++ b/net/socket.c
@@ -1657,12 +1657,36 @@ 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",
+ "A fmod_ret entry point for 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;
- sock = __sys_socket_create(family, type, protocol);
+ sock = __sys_socket_create(family, type,
+ update_socket_protocol(family, type, protocol));
if (IS_ERR(sock))
return PTR_ERR(sock);
