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/src/usr.bin/nc/nc.1 b/src/usr.bin/nc/nc.1
index 4c2a055cc4..c7a5a2b6e4 100644
--- a/src/usr.bin/nc/nc.1
+++ b/src/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/src/usr.bin/nc/netcat.c b/src/usr.bin/nc/netcat.c
index 571de9a766..6997b321db 100644
--- a/src/usr.bin/nc/netcat.c
+++ b/src/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)