mptcp: fix rx timestamp corruption on fastopen

The skb cb offset containing the timestamp presence flag is cleared
before loading such information. Cache such value before MPTCP CB
initialization.

Fixes: 36b122baf6a8 ("mptcp: add subflow_v(4,6)_send_synack()")
Cc: stable@vger.kernel.org
Signed-off-by: Paolo Abeni <pabeni@redhat.com>
Reviewed-by: Matthieu Baerts (NGI0) <matttbe@kernel.org>
Signed-off-by: Matthieu Baerts (NGI0) <matttbe@kernel.org>
Link: https://patch.msgid.link/20260501-net-mptcp-misc-fixes-7-1-rc3-v1-3-b70118df778e@kernel.org
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

diff --git a/net/mptcp/fastopen.c b/net/mptcp/fastopen.c
index 82ec15bcfd7f5678b1e53a6abd611cfc760a8cd9..082c46c0f50ee7a32f5f703ac44381cf2d5c3b67 100644 (file)
--- a/net/mptcp/fastopen.c
+++ b/net/mptcp/fastopen.c
@@ -12,6 +12,7 @@ void mptcp_fastopen_subflow_synack_set_params(struct mptcp_subflow_context *subf
        struct sock *sk, *ssk;
        struct sk_buff *skb;
        struct tcp_sock *tp;
+       bool has_rxtstamp;
 
        /* on early fallback the subflow context is deleted by
         * subflow_syn_recv_sock()
@@ -40,12 +41,13 @@ void mptcp_fastopen_subflow_synack_set_params(struct mptcp_subflow_context *subf
         */
        tp->copied_seq += skb->len;
        subflow->ssn_offset += skb->len;
+       has_rxtstamp = TCP_SKB_CB(skb)->has_rxtstamp;
 
        /* Only the sequence delta is relevant */
        MPTCP_SKB_CB(skb)->map_seq = -skb->len;
        MPTCP_SKB_CB(skb)->end_seq = 0;
        MPTCP_SKB_CB(skb)->offset = 0;
-       MPTCP_SKB_CB(skb)->has_rxtstamp = TCP_SKB_CB(skb)->has_rxtstamp;
+       MPTCP_SKB_CB(skb)->has_rxtstamp = has_rxtstamp;
        MPTCP_SKB_CB(skb)->cant_coalesce = 1;
 
        mptcp_data_lock(sk);