linux-kernel - [PATCH net 1/3] mptcp: fix recvbuffer adjust on sleeping rcvmsg

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Message-Id: <20241230-net-mptcp-rbuf-fixes-v1-1-8608af434ceb@kernel.org>
Date: Mon, 30 Dec 2024 19:12:30 +0100
From: "Matthieu Baerts (NGI0)" <matttbe@...nel.org>
To: mptcp@...ts.linux.dev, Mat Martineau <martineau@...nel.org>, 
 Geliang Tang <geliang@...nel.org>, "David S. Miller" <davem@...emloft.net>, 
 Eric Dumazet <edumazet@...gle.com>, Jakub Kicinski <kuba@...nel.org>, 
 Paolo Abeni <pabeni@...hat.com>, Simon Horman <horms@...nel.org>
Cc: netdev@...r.kernel.org, linux-kernel@...r.kernel.org, 
 "Matthieu Baerts (NGI0)" <matttbe@...nel.org>, stable@...r.kernel.org
Subject: [PATCH net 1/3] mptcp: fix recvbuffer adjust on sleeping rcvmsg

From: Paolo Abeni <pabeni@...hat.com>

If the recvmsg() blocks after receiving some data - i.e. due to
SO_RCVLOWAT - the MPTCP code will attempt multiple times to
adjust the receive buffer size, wrongly accounting every time the
cumulative of received data - instead of accounting only for the
delta.

Address the issue moving mptcp_rcv_space_adjust just after the
data reception and passing it only the just received bytes.

This also removes an unneeded difference between the TCP and MPTCP
RX code path implementation.

Fixes: 581302298524 ("mptcp: error out earlier on disconnect")
Cc: stable@...r.kernel.org
Signed-off-by: Paolo Abeni <pabeni@...hat.com>
Reviewed-by: Mat Martineau <martineau@...nel.org>
Signed-off-by: Matthieu Baerts (NGI0) <matttbe@...nel.org>
---
 net/mptcp/protocol.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/net/mptcp/protocol.c b/net/mptcp/protocol.c
index 08a72242428c0348471a5995465aec32c67af347..27afdb7e2071b16dbc4dfa1199b6e78c784f7a7c 100644
--- a/net/mptcp/protocol.c
+++ b/net/mptcp/protocol.c
@@ -1939,6 +1939,8 @@ static int mptcp_sendmsg(struct sock *sk, struct msghdr *msg, size_t len)
 	goto out;
 }

+static void mptcp_rcv_space_adjust(struct mptcp_sock *msk, int copied);
+
 static int __mptcp_recvmsg_mskq(struct mptcp_sock *msk,
 				struct msghdr *msg,
 				size_t len, int flags,
@@ -1992,6 +1994,7 @@ static int __mptcp_recvmsg_mskq(struct mptcp_sock *msk,
 			break;
 	}

+	mptcp_rcv_space_adjust(msk, copied);
 	return copied;
 }

@@ -2268,7 +2271,6 @@ static int mptcp_recvmsg(struct sock *sk, struct msghdr *msg, size_t len,
 		}

 		pr_debug("block timeout %ld\n", timeo);
-		mptcp_rcv_space_adjust(msk, copied);
 		err = sk_wait_data(sk, &timeo, NULL);
 		if (err < 0) {
 			err = copied ? : err;
@@ -2276,8 +2278,6 @@ static int mptcp_recvmsg(struct sock *sk, struct msghdr *msg, size_t len,
 		}
 	}

-	mptcp_rcv_space_adjust(msk, copied);
-
 out_err:
 	if (cmsg_flags && copied >= 0) {
 		if (cmsg_flags & MPTCP_CMSG_TS)

-- 
2.47.1