From: Aron Xu <aron@debian.org>
Date: Mon, 13 Feb 2012 19:06:52 +0800
Subject: misc connection failures
---
nc.1 | 76 ++++++++++++++++++++++++++++++++++++---
netcat.c | 119 ++++++++++++++++++++++++++++++++++++++++++--------------------
2 files changed, 153 insertions(+), 42 deletions(-)
diff --git a/nc.1 b/nc.1
index 60e3668..477cb1b 100644
--- a/nc.1
+++ b/nc.1
@@ -34,7 +34,7 @@
.Sh SYNOPSIS
.Nm nc
.Bk -words
-.Op Fl 46CDdhklnrStUuvZz
+.Op Fl 46bCDdhklnrStUuvZz
.Op Fl I Ar length
.Op Fl i Ar interval
.Op Fl O Ar length
@@ -99,6 +99,8 @@ to use IPv4 addresses only.
Forces
.Nm
to use IPv6 addresses only.
+.It Fl b
+Allow broadcast.
.It Fl C
Send CRLF as line-ending.
.It Fl D
@@ -323,6 +325,54 @@ and which side is being used as a
The connection may be terminated using an
.Dv EOF
.Pq Sq ^D .
+.Pp
+There is no
+.Fl c
+or
+.Fl e
+option in this netcat, but you still can execute a command after connection
+being established by redirecting file descriptors. Be cautious here because
+opening a port and let anyone connected execute arbitrary command on your
+site is DANGEROUS. If you really need to do this, here is an example:
+.Pp
+On
+.Sq server
+side:
+.Pp
+.Dl $ rm -f /tmp/f; mkfifo /tmp/f
+.Dl $ cat /tmp/f | /bin/sh -i 2>&1 | nc -l 127.0.0.1 1234 > /tmp/f
+.Pp
+On
+.Sq client
+side:
+.Pp
+.Dl $ nc host.example.com 1234
+.Dl $ (shell prompt from host.example.com)
+.Pp
+By doing this, you create a fifo at /tmp/f and make nc listen at port 1234
+of address 127.0.0.1 on
+.Sq server
+side, when a
+.Sq client
+establishes a connection successfully to that port, /bin/sh gets executed
+on
+.Sq server
+side and the shell prompt is given to
+.Sq client
+side.
+.Pp
+When connection is terminated,
+.Nm
+quits as well. Use
+.Fl k
+if you want it keep listening, but if the command quits this option won't
+restart it or keep
+.Nm
+running. Also don't forget to remove the file descriptor once you don't need
+it anymore:
+.Pp
+.Dl $ rm -f /tmp/f
+.Pp
.Sh DATA TRANSFER
The example in the previous section can be expanded to build a
basic data transfer model.
@@ -382,15 +432,30 @@ The
flag can be used to tell
.Nm
to report open ports,
-rather than initiate a connection.
+rather than initiate a connection. Usually it's useful to turn on verbose
+output to stderr by use this option in conjunction with
+.Fl v
+option.
+.Pp
For example:
.Bd -literal -offset indent
-$ nc -z host.example.com 20-30
+$ nc \-zv host.example.com 20-30
Connection to host.example.com 22 port [tcp/ssh] succeeded!
Connection to host.example.com 25 port [tcp/smtp] succeeded!
.Ed
.Pp
-The port range was specified to limit the search to ports 20 \- 30.
+The port range was specified to limit the search to ports 20 \- 30, and is
+scanned by increasing order.
+.Pp
+You can also specify a list of ports to scan, for example:
+.Bd -literal -offset indent
+$ nc \-zv host.example.com 80 20 22
+nc: connect to host.example.com 80 (tcp) failed: Connection refused
+nc: connect to host.example.com 20 (tcp) failed: Connection refused
+Connection to host.example.com port [tcp/ssh] succeeded!
+.Ed
+.Pp
+The ports are scanned by the order you given.
.Pp
Alternatively, it might be useful to know which server software
is running, and which versions.
@@ -455,6 +520,9 @@ Original implementation by *Hobbit*
.br
Rewritten with IPv6 support by
.An Eric Jackson Aq ericj@monkey.org .
+.br
+Modified for Debian port by Aron Xu
+.Aq aron@debian.org .
.Sh CAVEATS
UDP port scans using the
.Fl uz
diff --git a/netcat.c b/netcat.c
index bf9940f..c938d11 100644
--- a/netcat.c
+++ b/netcat.c
@@ -88,6 +88,7 @@
#include <netdb.h>
#include <poll.h>
#include <signal.h>
+#include <stddef.h>
#include <stdarg.h>
#include <stdio.h>
#include <stdlib.h>
@@ -115,6 +116,7 @@
#define UDP_SCAN_TIMEOUT 3 /* Seconds */
/* Command Line Options */
+int bflag; /* Allow Broadcast */
int Cflag = 0; /* CRLF line-ending */
int dflag; /* detached, no stdin */
unsigned int iflag; /* Interval Flag */
@@ -146,7 +148,7 @@ char *portlist[PORT_MAX+1];
char *unix_dg_tmp_socket;
void atelnet(int, unsigned char *, unsigned int);
-void build_ports(char *);
+void build_ports(char **);
void help(void);
int local_listen(char *, char *, struct addrinfo);
void readwrite(int);
@@ -171,11 +173,14 @@ int
main(int argc, char *argv[])
{
int ch, s, ret, socksv;
- char *host, *uport;
+ char *host, **uport;
struct addrinfo hints;
struct servent *sv;
socklen_t len;
- struct sockaddr_storage cliaddr;
+ union {
+ struct sockaddr_storage storage;
+ struct sockaddr_un forunix;
+ } cliaddr;
char *proxy = NULL;
const char *errstr, *proxyhost = "", *proxyport = NULL;
struct addrinfo proxyhints;
@@ -189,7 +194,7 @@ main(int argc, char *argv[])
sv = NULL;
while ((ch = getopt(argc, argv,
- "46CDdhI:i:jklnO:P:p:q:rSs:tT:UuV:vw:X:x:Zz")) != -1) {
+ "46bCDdhI:i:jklnO:P:p:q:rSs:tT:UuV:vw:X:x:Zz")) != -1) {
switch (ch) {
case '4':
family = AF_INET;
@@ -197,6 +202,13 @@ main(int argc, char *argv[])
case '6':
family = AF_INET6;
break;
+ case 'b':
+# if defined(SO_BROADCAST)
+ bflag = 1;
+# else
+ errx(1, "no broadcast frame support available");
+# endif
+ break;
case 'U':
family = AF_UNIX;
break;
@@ -342,35 +354,40 @@ main(int argc, char *argv[])
/* Cruft to make sure options are clean, and used properly. */
if (argv[0] && !argv[1] && family == AF_UNIX) {
- if (uflag)
- errx(1, "cannot use -u and -U");
# if defined(IPPROTO_DCCP) && defined(SOCK_DCCP)
if (dccpflag)
errx(1, "cannot use -Z and -U");
# endif
host = argv[0];
uport = NULL;
- } else if (!argv[0] && lflag) {
- if (sflag)
- errx(1, "cannot use -s and -l");
- if (zflag)
- errx(1, "cannot use -z and -l");
- if (pflag)
- uport=pflag;
- } else if (!lflag && kflag) {
- errx(1, "cannot use -k without -l");
- } else if (argv[0] && !argv[1]) {
- if (!lflag)
- usage(1);
- uport = argv[0];
+ } else if (argv[0] && !argv[1] && lflag) {
+ if (pflag) {
+ uport = &pflag;
+ host = argv[0];
+ } else {
+ uport = argv;
+ host = NULL;
+ }
+ } else if (!argv[0] && lflag && pflag) {
+ uport = &pflag;
host = NULL;
} else if (argv[0] && argv[1]) {
host = argv[0];
- uport = argv[1];
+ uport = &argv[1];
} else
usage(1);
-
+ if (lflag) {
+ if (sflag)
+ errx(1, "cannot use -s and -l");
+ if (zflag)
+ errx(1, "cannot use -z and -l");
+ if (pflag)
+ /* This still does not work well because of getopt mess
+ errx(1, "cannot use -p and -l"); */
+ uport = &pflag;
+ } else if (!lflag && kflag)
+ errx(1, "cannot use -k without -l");
/* Get name of temporary socket for unix datagram client */
if ((family == AF_UNIX) && uflag && !lflag) {
@@ -448,7 +465,7 @@ main(int argc, char *argv[])
else
s = unix_listen(host);
} else
- s = local_listen(host, uport, hints);
+ s = local_listen(host, *uport, hints);
if (s < 0)
err(1, NULL);
@@ -457,7 +474,8 @@ main(int argc, char *argv[])
local = ":::";
else
local = "0.0.0.0";
- fprintf(stderr, "Listening on [%s] (family %d, port %d)\n",
+ if (vflag && (family != AF_UNIX))
+ fprintf(stderr, "Listening on [%s] (family %d, port %s)\n",
host ?: local,
family,
*uport);
@@ -490,13 +508,17 @@ main(int argc, char *argv[])
len = sizeof(cliaddr);
connfd = accept(s, (struct sockaddr *)&cliaddr,
&len);
- if(vflag) {
+ if(vflag && family == AF_UNIX) {
+ fprintf(stderr, "Connection from \"%.*s\" accepted\n",
+ (len - (int)offsetof(struct sockaddr_un, sun_path)),
+ ((struct sockaddr_un*)&cliaddr)->sun_path);
+ } else if(vflag) {
char *proto = proto_name(uflag, dccpflag);
/* Don't look up port if -n. */
if (nflag)
sv = NULL;
else
- sv = getservbyport(ntohs(atoi(uport)),
+ sv = getservbyport(ntohs(atoi(*uport)),
proto);
if (((struct sockaddr *)&cliaddr)->sa_family == AF_INET) {
@@ -504,7 +526,7 @@ main(int argc, char *argv[])
inet_ntop(((struct sockaddr *)&cliaddr)->sa_family,&(((struct sockaddr_in *)&cliaddr)->sin_addr),dst,INET_ADDRSTRLEN);
fprintf(stderr, "Connection from [%s] port %s [%s/%s] accepted (family %d, sport %d)\n",
dst,
- uport,
+ *uport,
proto,
sv ? sv->s_name : "*",
((struct sockaddr *)(&cliaddr))->sa_family,
@@ -515,7 +537,7 @@ main(int argc, char *argv[])
inet_ntop(((struct sockaddr *)&cliaddr)->sa_family,&(((struct sockaddr_in6 *)&cliaddr)->sin6_addr),dst,INET6_ADDRSTRLEN);
fprintf(stderr, "Connection from [%s] port %s [%s/%s] accepted (family %d, sport %d)\n",
dst,
- uport,
+ *uport,
proto,
sv ? sv->s_name : "*",
((struct sockaddr *)&cliaddr)->sa_family,
@@ -523,17 +545,21 @@ main(int argc, char *argv[])
}
else {
fprintf(stderr, "Connection from unknown port %s [%s/%s] accepted (family %d, sport %d)\n",
- uport,
+ *uport,
proto,
sv ? sv->s_name : "*",
((struct sockaddr *)(&cliaddr))->sa_family,
ntohs(((struct sockaddr_in *)&cliaddr)->sin_port));
}
}
+ if(!kflag)
+ close(s);
readwrite(connfd);
close(connfd);
}
+ if (vflag && kflag)
+ fprintf(stderr, "Connection closed, listening again.\n");
if (kflag)
continue;
if (family != AF_UNIX) {
@@ -641,6 +667,8 @@ unix_bind(char *path)
return (-1);
}
+ unlink(path);
+
if (bind(s, (struct sockaddr *)&sun, SUN_LEN(&sun)) < 0) {
close(s);
return (-1);
@@ -662,8 +690,10 @@ unix_connect(char *path)
if ((s = unix_bind(unix_dg_tmp_socket)) < 0)
return (-1);
} else {
- if ((s = socket(AF_UNIX, SOCK_STREAM, 0)) < 0)
+ if ((s = socket(AF_UNIX, SOCK_STREAM, 0)) < 0) {
+ errx(1,"create unix socket failed");
return (-1);
+ }
}
(void)fcntl(s, F_SETFD, 1);
@@ -674,9 +704,11 @@ unix_connect(char *path)
sizeof(sun.sun_path)) {
close(s);
errno = ENAMETOOLONG;
+ warn("unix connect abandoned");
return (-1);
}
if (connect(s, (struct sockaddr *)&sun, SUN_LEN(&sun)) < 0) {
+ warn("unix connect failed");
close(s);
return (-1);
}
@@ -1105,22 +1137,23 @@ atelnet(int nfd, unsigned char *buf, unsigned int size)
* that we should try to connect to.
*/
void
-build_ports(char *p)
+build_ports(char **p)
{
struct servent *sv;
const char *errstr;
char *n;
int hi, lo, cp;
int x = 0;
+ int i;
char *proto = proto_name(uflag, dccpflag);
- sv = getservbyname(p, proto);
+ sv = getservbyname(*p, proto);
if (sv) {
portlist[0] = calloc(1, PORT_MAX_LEN);
if (portlist[0] == NULL)
err(1, NULL);
snprintf(portlist[0], PORT_MAX_LEN, "%d", ntohs(sv->s_port));
- } else if ((n = strchr(p, '-')) != NULL) {
+ } else if ((n = strchr(*p, '-')) != NULL) {
*n = '\0';
n++;
@@ -1128,9 +1161,9 @@ build_ports(char *p)
hi = strtonum(n, 1, PORT_MAX, &errstr);
if (errstr)
errx(1, "port number %s: %s", errstr, n);
- lo = strtonum(p, 1, PORT_MAX, &errstr);
+ lo = strtonum(*p, 1, PORT_MAX, &errstr);
if (errstr)
- errx(1, "port number %s: %s", errstr, p);
+ errx(1, "port number %s: %s", errstr, *p);
if (lo > hi) {
cp = hi;
@@ -1160,10 +1193,12 @@ build_ports(char *p)
}
}
} else {
- hi = strtonum(p, 1, PORT_MAX, &errstr);
+ hi = strtonum(*p, 1, PORT_MAX, &errstr);
if (errstr)
- errx(1, "port number %s: %s", errstr, p);
- portlist[0] = strdup(p);
+ errx(1, "port number %s: %s", errstr, *p);
+ for (i=0;p[i];i++) {
+ portlist[i] = strdup(p[i]);
+ }
if (portlist[0] == NULL)
err(1, NULL);
}
@@ -1198,6 +1233,13 @@ set_common_sockopts(int s)
{
int x = 1;
+# if defined(SO_BROADCAST)
+ if (bflag) {
+ if (setsockopt(s, IPPROTO_TCP, SO_BROADCAST,
+ &x, sizeof(x)) == -1)
+ err(1, NULL);
+ }
+# endif
# if defined(TCP_MD5SIG)
if (Sflag) {
if (setsockopt(s, IPPROTO_TCP, TCP_MD5SIG,
@@ -1293,6 +1335,7 @@ help(void)
fprintf(stderr, "\tCommand Summary:\n\
\t-4 Use IPv4\n\
\t-6 Use IPv6\n\
+ \t-b Allow broadcast\n\
\t-C Send CRLF as line-ending\n\
\t-D Enable the debug socket option\n\
\t-d Detach from stdin\n\
@@ -1329,7 +1372,7 @@ void
usage(int ret)
{
fprintf(stderr,
- "usage: nc [-46CDdhjklnrStUuvZz] [-I length] [-i interval] [-O length]\n"
+ "usage: nc [-46bCDdhjklnrStUuvZz] [-I length] [-i interval] [-O length]\n"
"\t [-P proxy_username] [-p source_port] [-q seconds] [-s source]\n"
"\t [-T toskeyword] [-V rtable] [-w timeout] [-X proxy_protocol]\n"
"\t [-x proxy_address[:port]] [destination] [port]\n");
--
|
