From: Gang Yan <yangang@kylinos.cn>

bpf_setsockopt() currently cannot be used on mptcp master sockets:
__bpf_setsockopt() dispatches by level to the protocol-agnostic
sol_*_sockopt() helpers, which either reject the msk
(sk_protocol == IPPROTO_MPTCP) and the ssk (sk_is_tcp() is false)
or bypass mptcp's own dispatch (e.g. SOL_IP going straight to
do_ip_setsockopt()).

This patch routes any level to mptcp_setsockopt(), which already
handles all levels.

Signed-off-by: Gang Yan <yangang@kylinos.cn>
---
 include/net/mptcp.h | 9 +++++++++
 net/core/filter.c   | 7 +++++++
 2 files changed, 16 insertions(+)

diff --git a/include/net/mptcp.h b/include/net/mptcp.h
index 333bde2a0b76..fcce2b7e9ef9 100644
--- a/include/net/mptcp.h
+++ b/include/net/mptcp.h
@@ -237,6 +237,9 @@ static inline __be32 mptcp_reset_option(const struct sk_buff *skb)
 }
 
 void mptcp_active_detect_blackhole(struct sock *sk, bool expired);
+
+int mptcp_setsockopt(struct sock *sk, int level, int optname,
+		     sockptr_t optval, unsigned int optlen);
 #else
 
 static inline void mptcp_init(void)
@@ -314,6 +317,12 @@ static inline struct request_sock *mptcp_subflow_reqsk_alloc(const struct reques
 static inline __be32 mptcp_reset_option(const struct sk_buff *skb)  { return htonl(0u); }
 
 static inline void mptcp_active_detect_blackhole(struct sock *sk, bool expired) { }
+
+static inline int mptcp_setsockopt(struct sock *sk, int level, int optname,
+				   sockptr_t optval, unsigned int optlen)
+{
+	return -EINVAL;
+}
 #endif /* CONFIG_MPTCP */
 
 #if IS_ENABLED(CONFIG_MPTCP_IPV6)
diff --git a/net/core/filter.c b/net/core/filter.c
index b446aa8be5c3..18e650bf7393 100644
--- a/net/core/filter.c
+++ b/net/core/filter.c
@@ -5683,6 +5683,13 @@ static int __bpf_setsockopt(struct sock *sk, int level, int optname,
 	if (!sk_fullsock(sk))
 		return -EINVAL;
 
+	/* Route any bpf_setsockopt on the mptcp socket to mptcp_setsockopt,
+	 * which handles all levels.
+	 */
+	if (IS_ENABLED(CONFIG_MPTCP) && sk->sk_protocol == IPPROTO_MPTCP)
+		return mptcp_setsockopt(sk, level, optname,
+					KERNEL_SOCKPTR(optval), optlen);
+
 	if (level == SOL_SOCKET)
 		return sol_socket_sockopt(sk, optname, optval, &optlen, false);
 	else if (IS_ENABLED(CONFIG_INET) && level == SOL_IP)
-- 
2.43.0