add -F flag to enabled fd-pass mode: establish connection and pass

connected socket to stdout. This is useful in proxy mode to establish
a connection for use by ssh in conjunction with its new ProxyUseFDPass
option; ok markus@

2 files changed, 89 insertions, 6 deletions

diff --git a/usr.bin/nc/nc.1 b/usr.bin/nc/nc.1
index 4c2a055cc45..c7a5a2b6e43 100644
--- a/usr.bin/nc/nc.1
+++ b/usr.bin/nc/nc.1
@@ -1,4 +1,4 @@
-.\"     $OpenBSD: nc.1,v 1.63 2013/07/16 00:07:52 schwarze Exp $
+.\"     $OpenBSD: nc.1,v 1.64 2013/08/20 16:22:09 djm Exp $
 .\"
 .\" Copyright (c) 1996 David Sacerdote
 .\" All rights reserved.
@@ -25,7 +25,7 @@
 .\" (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
 .\" THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 .\"
-.Dd $Mdocdate: July 16 2013 $
+.Dd $Mdocdate: August 20 2013 $
 .Dt NC 1
 .Os
 .Sh NAME
@@ -34,7 +34,7 @@
 .Sh SYNOPSIS
 .Nm nc
 .Bk -words
-.Op Fl 46DdhklNnrStUuvz
+.Op Fl 46DdFhklNnrStUuvz
 .Op Fl I Ar length
 .Op Fl i Ar interval
 .Op Fl O Ar length
@@ -102,6 +102,21 @@ to use IPv6 addresses only.
 Enable debugging on the socket.
 .It Fl d
 Do not attempt to read from stdin.
+.It Fl F
+Pass the first connected socket using
+.Xr sendmsg 2
+to stdout and exit.
+This is useful in conjunction with
+.Fl X
+to have
+.Nm
+perform connection setup with a proxy but then leave the rest of the
+connection to another program (e.g.
+.Xr ssh 1
+using the
+.Xr ssh_config 5
+.Cm ProxyUseFdPass
+option).
 .It Fl h
 Prints out
 .Nm
diff --git a/usr.bin/nc/netcat.c b/usr.bin/nc/netcat.c
index 571de9a7666..6997b321db2 100644
--- a/usr.bin/nc/netcat.c
+++ b/usr.bin/nc/netcat.c
@@ -1,4 +1,4 @@
-/* $OpenBSD: netcat.c,v 1.112 2013/04/29 00:28:23 okan Exp $ */
+/* $OpenBSD: netcat.c,v 1.113 2013/08/20 16:22:09 djm Exp $ */
 /*
  * Copyright (c) 2001 Eric Jackson <ericj@monkey.org>
  *
@@ -34,6 +34,7 @@
 #include <sys/types.h>
 #include <sys/socket.h>
 #include <sys/time.h>
+#include <sys/uio.h>
 #include <sys/un.h>
 
 #include <netinet/in.h>
@@ -66,6 +67,7 @@
 
 /* Command Line Options */
 int	dflag;					/* detached, no stdin */
+int	Fflag;					/* fdpass sock to stdout */
 unsigned int iflag;				/* Interval Flag */
 int	kflag;					/* More than one connect */
 int	lflag;					/* Bind to local port */
@@ -97,6 +99,7 @@ void	build_ports(char *);
 void	help(void);
 int	local_listen(char *, char *, struct addrinfo);
 void	readwrite(int);
+void	fdpass(int nfd) __attribute__((noreturn));
 int	remote_connect(const char *, const char *, struct addrinfo);
 int	timeout_connect(int, const struct sockaddr *, socklen_t);
 int	socks_connect(const char *, const char *, struct addrinfo,
@@ -132,7 +135,7 @@ main(int argc, char *argv[])
 	sv = NULL;
 
 	while ((ch = getopt(argc, argv,
-	    "46DdhI:i:klNnO:P:p:rSs:tT:UuV:vw:X:x:z")) != -1) {
+	    "46DdFhI:i:klNnO:P:p:rSs:tT:UuV:vw:X:x:z")) != -1) {
 		switch (ch) {
 		case '4':
 			family = AF_INET;
@@ -156,6 +159,9 @@ main(int argc, char *argv[])
 		case 'd':
 			dflag = 1;
 			break;
+		case 'F':
+			Fflag = 1;
+			break;
 		case 'h':
 			help();
 			break;
@@ -463,7 +469,9 @@ main(int argc, char *argv[])
 				    uflag ? "udp" : "tcp",
 				    sv ? sv->s_name : "*");
 			}
-			if (!zflag)
+			if (Fflag)
+				fdpass(s);
+			else if (!zflag)
 				readwrite(s);
 		}
 	}
@@ -787,6 +795,66 @@ readwrite(int nfd)
 	}
 }
 
+/*
+ * fdpass()
+ * Pass the connected file descriptor to stdout and exit.
+ */
+void
+fdpass(int nfd)
+{
+	struct msghdr mh;
+	union {
+		struct cmsghdr hdr;
+		char buf[CMSG_SPACE(sizeof(int))];
+	} cmsgbuf;
+	struct cmsghdr *cmsg;
+	struct iovec iov;
+	char c = '\0';
+	ssize_t r;
+	struct pollfd pfd;
+
+	/* Avoid obvious stupidity */
+	if (isatty(STDOUT_FILENO))
+		errx(1, "Cannot pass file descriptor to tty");
+
+	bzero(&mh, sizeof(mh));
+	bzero(&cmsgbuf, sizeof(cmsgbuf));
+	bzero(&iov, sizeof(iov));
+	bzero(&pfd, sizeof(pfd));
+
+	mh.msg_control = (caddr_t)&cmsgbuf.buf;
+	mh.msg_controllen = sizeof(cmsgbuf.buf);
+	cmsg = CMSG_FIRSTHDR(&mh);
+	cmsg->cmsg_len = CMSG_LEN(sizeof(int));
+	cmsg->cmsg_level = SOL_SOCKET;
+	cmsg->cmsg_type = SCM_RIGHTS;
+	*(int *)CMSG_DATA(cmsg) = nfd;
+
+	iov.iov_base = &c;
+	iov.iov_len = 1;
+	mh.msg_iov = &iov;
+	mh.msg_iovlen = 1;
+
+	bzero(&pfd, sizeof(pfd));
+	pfd.fd = STDOUT_FILENO;
+	for (;;) {
+		r = sendmsg(STDOUT_FILENO, &mh, 0);
+		if (r == -1) {
+			if (errno == EAGAIN || errno == EINTR) {
+				pfd.events = POLLOUT;
+				if (poll(&pfd, 1, -1) == -1)
+					err(1, "poll");
+				continue;
+			}
+			err(1, "sendmsg");
+		} else if (r == -1)
+			errx(1, "sendmsg: unexpected return value %zd", r);
+		else
+			break;
+	}
+	exit(0);
+}
+
 /* Deal with RFC 854 WILL/WONT DO/DONT negotiation. */
 void
 atelnet(int nfd, unsigned char *buf, unsigned int size)