mptcp: fix rx timestamp corruption on fastopen

commit 6254a16d6f0c672e3809ca5d7c9a28a55d71f764 upstream.

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>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.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);