Fix -N flag to actually shut down the (entire) socket when the input

goes away. This allows for using nc in cases where the network server
will no longer expect anything after eof, instead of hanging waiting
for more input from our end.

Additionaly, shut down if tls is in use if either side of the socket
goes away, since we higher level TLS operations (tls_read and write)
will require the socket to be both readable and writable as we can
get TLS_WANT_POLLIN or TLS_WANT_POLLOUT on either operation.

deraadt@ buying it.  found by sthen@

1 files changed, 18 insertions, 1 deletions

diff --git a/src/usr.bin/nc/netcat.c b/src/usr.bin/nc/netcat.c
index c04298f64c..795592f0b7 100644
--- a/src/usr.bin/nc/netcat.c
+++ b/src/usr.bin/nc/netcat.c
@@ -1,4 +1,4 @@
-/* $OpenBSD: netcat.c,v 1.206 2019/08/08 16:49:35 mestre Exp $ */
+/* $OpenBSD: netcat.c,v 1.207 2019/10/17 14:29:24 beck Exp $ */
 /*
  * Copyright (c) 2001 Eric Jackson <ericj@monkey.org>
  * Copyright (c) 2015 Bob Beck.  All rights reserved.
@@ -1259,6 +1259,23 @@ readwrite(int net_fd, struct tls *tls_ctx)
                 if (pfd[POLL_NETIN].fd == -1 && netinbufpos == 0) {
                         pfd[POLL_STDOUT].fd = -1;
                 }
+
+                if (((usetls || Nflag) && (pfd[POLL_NETIN].fd == -1)) ||
+                    (usetls && pfd[POLL_NETOUT].fd == -1)) {
+                        /*
+                         * -N says: shutdown(2) the 'network socket'
+                         * after EOF on the input
+                         *
+                         * for TLS we need to die if either end is
+                         * toast, since both reading and writing to
+                         * the socket may be necessary for any higher
+                         * level tls operation
+                         */
+                        shutdown(pfd[POLL_NETOUT].fd, SHUT_WR);
+                        shutdown(pfd[POLL_NETIN].fd, SHUT_RD);
+                        pfd[POLL_NETOUT].fd = -1;
+                        pfd[POLL_NETIN].fd = -1;
+                }
         }
 }