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mptcp: fix ack generation for fallback msk

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commit 5e15395f6d upstream.

mptcp_cleanup_rbuf() needs to know the last most recent, mptcp-level
rcv_wnd sent, and such information is tracked into the msk->old_wspace
field, updated at ack transmission time by mptcp_write_options().

Fallback socket do not add any mptcp options, such helper is never
invoked, and msk->old_wspace value remain stale. That in turn makes
ack generation at recvmsg() time quite random.

Address the issue ensuring mptcp_write_options() is invoked even for
fallback sockets, and just update the needed info in such a case.

The issue went unnoticed for a long time, as mptcp currently overshots
the fallback socket receive buffer autotune significantly. It is going
to change in the near future.

Fixes: e3859603ba ("mptcp: better msk receive window updates")
Cc: stable@vger.kernel.org
Closes: https://github.com/multipath-tcp/mptcp_net-next/issues/594
Signed-off-by: Paolo Abeni <pabeni@redhat.com>
Reviewed-by: Geliang Tang <geliang@kernel.org>
Reviewed-by: Matthieu Baerts (NGI0) <matttbe@kernel.org>
Signed-off-by: Matthieu Baerts (NGI0) <matttbe@kernel.org>
Link: https://patch.msgid.link/20251118-net-mptcp-misc-fixes-6-18-rc6-v1-1-806d3781c95f@kernel.org
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Paolo Abeni
2025-11-18 08:20:19 +01:00
committed by Greg Kroah-Hartman
parent ac28dfdded
commit ae43625bcc
1 changed files with 22 additions and 1 deletions
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23
net/mptcp/options.c
View File

@@ -839,8 +839,11 @@ bool mptcp_established_options(struct sock *sk, struct sk_buff *skb,
opts->suboptions = 0;
/* Force later mptcp_write_options(), but do not use any actual
* option space.
*/
if (unlikely(__mptcp_check_fallback(msk) && !mptcp_check_infinite_map(skb)))
return false;
return true;
if (unlikely(skb && TCP_SKB_CB(skb)->tcp_flags & TCPHDR_RST)) {
if (mptcp_established_options_fastclose(sk, &opt_size, remaining, opts) ||
@@ -1319,6 +1322,20 @@ update_wspace:
WRITE_ONCE(msk->old_wspace, tp->rcv_wnd);
}
static void mptcp_track_rwin(struct tcp_sock *tp)
{
const struct sock *ssk = (const struct sock *)tp;
struct mptcp_subflow_context *subflow;
struct mptcp_sock *msk;
if (!ssk)
return;
subflow = mptcp_subflow_ctx(ssk);
msk = mptcp_sk(subflow->conn);
WRITE_ONCE(msk->old_wspace, tp->rcv_wnd);
}
__sum16 __mptcp_make_csum(u64 data_seq, u32 subflow_seq, u16 data_len, __wsum sum)
{
struct csum_pseudo_header header;
@@ -1611,6 +1628,10 @@ mp_rst:
opts->reset_transient,
opts->reset_reason);
return;
} else if (unlikely(!opts->suboptions)) {
/* Fallback to TCP */
mptcp_track_rwin(tp);
return;
}
if (OPTION_MPTCP_PRIO & opts->suboptions) {