[PATCH 5.7 77/79] mptcp: fix bogus sendmsg() return code under pressure

Greg Kroah-Hartman
2020-08-10T15:38:26Z

From: Paolo Abeni <pabeni@redhat.com>

[ Upstream commit 8555c6bfd5fddb1cf363d3cd157d70a1bb27f718 ]

In case of memory pressure, mptcp_sendmsg() may call
sk_stream_wait_memory() after succesfully xmitting some
bytes. If the latter fails we currently return to the
user-space the error code, ignoring the succeful xmit.

Address the issue always checking for the xmitted bytes
before mptcp_sendmsg() completes.

Fixes: f296234c98a8 ("mptcp: Add handling of incoming MP_JOIN requests")
Reviewed-by: Matthieu Baerts <matthieu.baerts@tessares.net>
Signed-off-by: Paolo Abeni <pabeni@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
net/mptcp/protocol.c | 3 +--
1 file changed, 1 insertion(+), 2 deletions(-)

--- a/net/mptcp/protocol.c
+++ b/net/mptcp/protocol.c
@@ -802,7 +802,6 @@ fallback:

mptcp_set_timeout(sk, ssk);
if (copied) {
- ret = copied;
tcp_push(ssk, msg->msg_flags, mss_now, tcp_sk(ssk)->nonagle,
size_goal);

@@ -815,7 +814,7 @@ fallback:
release_sock(ssk);
out:
release_sock(sk);
- return ret;
+ return copied ? : ret;
}

static void mptcp_wait_data(struct sock *sk, long *timeo)