mptcp: update window_clamp on subflows when SO_RCVBUF is set

Add __mptcp_subflow_set_rcvbuf() helper to write the subflow sk_rcvbuf,
but also to call the recently added tcp_set_rcvbuf() helper to update
window_clamp. This is needed because the window clap is updated when
scaling_ratio changes, in tcp_measure_rcv_mss(). Until scaling_ratio
changes, the subflow is stuck with the old window clamp which may be
based on a small initial buffer.

Use this new helper in both mptcp_sol_socket_sync_intval() (setsockopt
path) and sync_socket_options() (new subflow creation path).

Note that this patch depends on commit b025461303d8 ("tcp: update
window_clamp when SO_RCVBUF is set"): it fixes the issue on TCP side,
but the same fix is needed on MPTCP side as well.

Fixes: a2cbb1603943 ("tcp: Update window clamping condition")
Cc: stable@vger.kernel.org
Closes: https://github.com/multipath-tcp/mptcp_net-next/issues/619
Signed-off-by: Gang Yan <yangang@kylinos.cn>
Reviewed-by: Matthieu Baerts (NGI0) <matttbe@kernel.org>
Signed-off-by: Matthieu Baerts (NGI0) <matttbe@kernel.org>
Link: https://patch.msgid.link/20260515-net-mptcp-misc-fixes-7-1-rc4-v2-5-701e96419f2f@kernel.org
Signed-off-by: Paolo Abeni <pabeni@redhat.com>

diff --git a/net/mptcp/sockopt.c b/net/mptcp/sockopt.c
index 1cf608e7357bdac0cad1cba0c8fda14fc4b1cea0..87b5796d0135342e764341256153c118e598eb65 100644 (file)
--- a/net/mptcp/sockopt.c
+++ b/net/mptcp/sockopt.c
@@ -67,6 +67,12 @@ static int mptcp_get_int_option(struct mptcp_sock *msk, sockptr_t optval,
        return 0;
 }
 
+static void __mptcp_subflow_set_rcvbuf(struct sock *ssk, int val)
+{
+       WRITE_ONCE(ssk->sk_rcvbuf, val);
+       tcp_set_rcvbuf(ssk, val);
+}
+
 static void mptcp_sol_socket_sync_intval(struct mptcp_sock *msk, int optname, int val)
 {
        struct mptcp_subflow_context *subflow;
@@ -100,7 +106,7 @@ static void mptcp_sol_socket_sync_intval(struct mptcp_sock *msk, int optname, in
                case SO_RCVBUF:
                case SO_RCVBUFFORCE:
                        ssk->sk_userlocks |= SOCK_RCVBUF_LOCK;
-                       WRITE_ONCE(ssk->sk_rcvbuf, sk->sk_rcvbuf);
+                       __mptcp_subflow_set_rcvbuf(ssk, sk->sk_rcvbuf);
                        break;
                case SO_MARK:
                        if (READ_ONCE(ssk->sk_mark) != sk->sk_mark) {
@@ -1560,7 +1566,7 @@ static void sync_socket_options(struct mptcp_sock *msk, struct sock *ssk)
                        mptcp_subflow_ctx(ssk)->cached_sndbuf = sk->sk_sndbuf;
                }
                if (sk->sk_userlocks & SOCK_RCVBUF_LOCK)
-                       WRITE_ONCE(ssk->sk_rcvbuf, sk->sk_rcvbuf);
+                       __mptcp_subflow_set_rcvbuf(ssk, sk->sk_rcvbuf);
        }
 
        if (sock_flag(sk, SOCK_LINGER)) {