[PATCH 4.20 18/52] tcp: do not report TCP_CM_INQ of 0 for closed connections

From: Greg Kroah-Hartman
Date: Mon Mar 18 2019 - 05:46:15 EST

4.20-stable review patch. If anyone has any objections, please let me know.


From: Soheil Hassas Yeganeh <soheil@xxxxxxxxxx>

[ Upstream commit 6466e715651f9f358e60c5ea4880e4731325827f ]

Returning 0 as inq to userspace indicates there is no more data to
read, and the application needs to wait for EPOLLIN. For a connection
that has received FIN from the remote peer, however, the application
must continue reading until getting EOF (return value of 0
from tcp_recvmsg) or an error, if edge-triggered epoll (EPOLLET) is
being used. Otherwise, the application will never receive a new
EPOLLIN, since there is no epoll edge after the FIN.

Return 1 when there is no data left on the queue but the
connection has received FIN, so that the applications continue

Fixes: b75eba76d3d72 (tcp: send in-queue bytes in cmsg upon read)
Signed-off-by: Soheil Hassas Yeganeh <soheil@xxxxxxxxxx>
Acked-by: Neal Cardwell <ncardwell@xxxxxxxxxx>
Signed-off-by: Eric Dumazet <edumazet@xxxxxxxxxx>
Acked-by: Yuchung Cheng <ycheng@xxxxxxxxxx>
Signed-off-by: David S. Miller <davem@xxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
net/ipv4/tcp.c | 5 +++++
1 file changed, 5 insertions(+)

--- a/net/ipv4/tcp.c
+++ b/net/ipv4/tcp.c
@@ -1914,6 +1914,11 @@ static int tcp_inq_hint(struct sock *sk)
inq = tp->rcv_nxt - tp->copied_seq;
+ /* After receiving a FIN, tell the user-space to continue reading
+ * by returning a non-zero inq.
+ */
+ if (inq == 0 && sock_flag(sk, SOCK_DONE))
+ inq = 1;
return inq;