Merge branch 'mptcp-fix-a-couple-of-races'

Paolo Abeni says:

====================
mptcp: fix a couple of races

The first patch addresses a division by zero issue reported by Eric,
the second one solves a similar issue found by code inspection while
investigating the former.
====================

Link: https://patch.msgid.link/cover.1731060874.git.pabeni@redhat.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

Author: kuba-moo

net/mptcp/protocol.c

@@ -2082,7 +2082,8 @@ static void mptcp_rcv_space_adjust(struct mptcp_sock *msk, int copied)
 				slow = lock_sock_fast(ssk);
 				WRITE_ONCE(ssk->sk_rcvbuf, rcvbuf);
 				WRITE_ONCE(tcp_sk(ssk)->window_clamp, window_clamp);
-				tcp_cleanup_rbuf(ssk, 1);
+				if (tcp_can_send_ack(ssk))
+					tcp_cleanup_rbuf(ssk, 1);
 				unlock_sock_fast(ssk, slow);
 			}
 		}
@@ -2205,7 +2206,7 @@ static int mptcp_recvmsg(struct sock *sk, struct msghdr *msg, size_t len,
 		cmsg_flags = MPTCP_CMSG_INQ;
 
 	while (copied < len) {
-		int bytes_read;
+		int err, bytes_read;
 
 		bytes_read = __mptcp_recvmsg_mskq(msk, msg, len - copied, flags, &tss, &cmsg_flags);
 		if (unlikely(bytes_read < 0)) {
@@ -2267,9 +2268,16 @@ static int mptcp_recvmsg(struct sock *sk, struct msghdr *msg, size_t len,
 		}
 
 		pr_debug("block timeout %ld\n", timeo);
-		sk_wait_data(sk, &timeo, NULL);
+		mptcp_rcv_space_adjust(msk, copied);
+		err = sk_wait_data(sk, &timeo, NULL);
+		if (err < 0) {
+			err = copied ? : err;
+			goto out_err;
+		}
 	}
 
+	mptcp_rcv_space_adjust(msk, copied);
+
 out_err:
 	if (cmsg_flags && copied >= 0) {
 		if (cmsg_flags & MPTCP_CMSG_TS)
@@ -2285,8 +2293,6 @@ static int mptcp_recvmsg(struct sock *sk, struct msghdr *msg, size_t len,
 	pr_debug("msk=%p rx queue empty=%d:%d copied=%d\n",
 		 msk, skb_queue_empty_lockless(&sk->sk_receive_queue),
 		 skb_queue_empty(&msk->receive_queue), copied);
-	if (!(flags & MSG_PEEK))
-		mptcp_rcv_space_adjust(msk, copied);
 
 	release_sock(sk);
 	return copied;