[PATCH 5.15.y] mptcp: don't always assume copied data in mptcp_cleanup_rbuf()

["Matthieu Baerts (NGI0)" <matttbe@kernel.org>]

From: Paolo Abeni <pabeni@redhat.com>

commit 551844f26da2a9f76c0a698baaffa631d1178645 upstream.

Under some corner cases the MPTCP protocol can end-up invoking
mptcp_cleanup_rbuf() when no data has been copied, but such helper
assumes the opposite condition.

Explicitly drop such assumption and performs the costly call only
when strictly needed - before releasing the msk socket lock.

Fixes: fd8976790a6c ("mptcp: be careful on MPTCP-level ack.")
Cc: stable@vger.kernel.org
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/20241230-net-mptcp-rbuf-fixes-v1-2-8608af434ceb@kernel.org
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
[ Conflicts in this version, because commit 581302298524 ("mptcp: error
  out earlier on disconnect") has not been backported to this version,
  and there was no need to do so. The only conflict was in protocol.c,
  and easy to resolve: the context was different, but the same addition
  can still be made at the same spot in mptcp_recvmsg(). ]
Signed-off-by: Matthieu Baerts (NGI0) <matttbe@kernel.org>
---
 net/mptcp/protocol.c | 18 +++++++++---------
 1 file changed, 9 insertions(+), 9 deletions(-)

diff --git a/net/mptcp/protocol.c b/net/mptcp/protocol.c
index bcbb1f92ce24..f337dd3323a0 100644
--- a/net/mptcp/protocol.c
+++ b/net/mptcp/protocol.c
@@ -462,13 +462,13 @@ static void mptcp_send_ack(struct mptcp_sock *msk)
 		mptcp_subflow_send_ack(mptcp_subflow_tcp_sock(subflow));
 }
 
-static void mptcp_subflow_cleanup_rbuf(struct sock *ssk)
+static void mptcp_subflow_cleanup_rbuf(struct sock *ssk, int copied)
 {
 	bool slow;
 
 	slow = lock_sock_fast(ssk);
 	if (tcp_can_send_ack(ssk))
-		tcp_cleanup_rbuf(ssk, 1);
+		tcp_cleanup_rbuf(ssk, copied);
 	unlock_sock_fast(ssk, slow);
 }
 
@@ -485,7 +485,7 @@ static bool mptcp_subflow_could_cleanup(const struct sock *ssk, bool rx_empty)
 			      (ICSK_ACK_PUSHED2 | ICSK_ACK_PUSHED)));
 }
 
-static void mptcp_cleanup_rbuf(struct mptcp_sock *msk)
+static void mptcp_cleanup_rbuf(struct mptcp_sock *msk, int copied)
 {
 	int old_space = READ_ONCE(msk->old_wspace);
 	struct mptcp_subflow_context *subflow;
@@ -493,14 +493,14 @@ static void mptcp_cleanup_rbuf(struct mptcp_sock *msk)
 	int space =  __mptcp_space(sk);
 	bool cleanup, rx_empty;
 
-	cleanup = (space > 0) && (space >= (old_space << 1));
-	rx_empty = !__mptcp_rmem(sk);
+	cleanup = (space > 0) && (space >= (old_space << 1)) && copied;
+	rx_empty = !__mptcp_rmem(sk) && copied;
 
 	mptcp_for_each_subflow(msk, subflow) {
 		struct sock *ssk = mptcp_subflow_tcp_sock(subflow);
 
 		if (cleanup || mptcp_subflow_could_cleanup(ssk, rx_empty))
-			mptcp_subflow_cleanup_rbuf(ssk);
+			mptcp_subflow_cleanup_rbuf(ssk, copied);
 	}
 }
 
@@ -2098,9 +2098,6 @@ static int mptcp_recvmsg(struct sock *sk, struct msghdr *msg, size_t len,
 
 		copied += bytes_read;
 
-		/* be sure to advertise window change */
-		mptcp_cleanup_rbuf(msk);
-
 		if (skb_queue_empty(&msk->receive_queue) && __mptcp_move_skbs(msk))
 			continue;
 
@@ -2152,9 +2149,12 @@ static int mptcp_recvmsg(struct sock *sk, struct msghdr *msg, size_t len,
 		}
 
 		pr_debug("block timeout %ld\n", timeo);
+		mptcp_cleanup_rbuf(msk, copied);
 		sk_wait_data(sk, &timeo, NULL);
 	}
 
+	mptcp_cleanup_rbuf(msk, copied);
+
 out_err:
 	if (cmsg_flags && copied >= 0) {
 		if (cmsg_flags & MPTCP_CMSG_TS)
-- 
2.47.1