mptcp: do not account for OoO in mptcp_rcvbuf_grow()

MPTCP-level OoOs are physiological when multiple subflows are active
concurrently and will not cause retransmissions nor are caused by
drops.

Accounting for them in mptcp_rcvbuf_grow() causes the rcvbuf slowly
drifting towards tcp_rmem[2].

Remove such accounting. Note that subflows will still account for TCP-level
OoO when the MPTCP-level rcvbuf is propagated.

This also closes a subtle and very unlikely race condition with rcvspace
init; active sockets with user-space holding the msk-level socket lock,
could complete such initialization in the receive callback, after that the
first OoO data reaches the rcvbuf and potentially triggering a divide by
zero Oops.

Fixes: e118cdc34dd1 ("mptcp: rcvbuf auto-tuning improvement")
Signed-off-by: Paolo Abeni <pabeni@redhat.com>
Reviewed-by: Mat Martineau <martineau@kernel.org>
Signed-off-by: Matthieu Baerts (NGI0) <matttbe@kernel.org>
Link: https://patch.msgid.link/20260203-net-next-mptcp-misc-feat-6-20-v1-1-31ec8bfc56d1@kernel.org
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

diff --git a/net/mptcp/protocol.c b/net/mptcp/protocol.c
index 9b8c51937eb2acd78d8a552bc4c4d1047bf8f079..758a6dcb1d7baaabba7f62ec09917348bacad05e 100644 (file)
--- a/net/mptcp/protocol.c
+++ b/net/mptcp/protocol.c
@@ -224,9 +224,6 @@ static bool mptcp_rcvbuf_grow(struct sock *sk, u32 newval)
        do_div(grow, oldval);
        rcvwin += grow << 1;
 
-       if (!RB_EMPTY_ROOT(&msk->out_of_order_queue))
-               rcvwin += MPTCP_SKB_CB(msk->ooo_last_skb)->end_seq - msk->ack_seq;
-
        cap = READ_ONCE(net->ipv4.sysctl_tcp_rmem[2]);
 
        rcvbuf = min_t(u32, mptcp_space_from_win(sk, rcvwin), cap);
@@ -350,9 +347,6 @@ merge_right:
 end:
        skb_condense(skb);
        skb_set_owner_r(skb, sk);
-       /* do not grow rcvbuf for not-yet-accepted or orphaned sockets. */
-       if (sk->sk_socket)
-               mptcp_rcvbuf_grow(sk, msk->rcvq_space.space);
 }
 
 static void mptcp_init_skb(struct sock *ssk, struct sk_buff *skb, int offset,