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Re: [nmap-svn] r31378 - nmap-exp/d33tah/ncat-env-conninfo/ncat
From: d33 tah <d33tah () gmail com>
Date: Thu, 18 Jul 2013 15:29:49 +0200

2013/7/18 Henri Doreau <henri.doreau () gmail com>:
2013/7/17 d33 tah <d33tah () gmail com>:
Hi Henri,

+    *env = (LPTSTR) safe_realloc(*env, *env_size+added_value_len);
+
+    Snprintf(*env + *env_size-1, added_value_len, "%s=%s", name, value);
+
+    *env_size += added_value_len;
+    (*env)[*env_size] = '\0';
+    (*env)[*env_size-1] = '\0';
Why do you zero the last *two* indices? Safety? You might want to
check/use Snprintf return value too.

As Windows MSDN docs say, the environment description string contains
a NULL-separated array of key=value strings. Its ending is marked by
two NULL bytes - probably one for the end of string, and another to
make next string zero-bytes long.

Thanks, I see.

+}
+
+static void setup_environment(struct fdinfo *info, LPTSTR* env, int *env_size)
+{
+    char *dest_addr=NULL;
+    char dest_port[10];
+    union sockaddr_u su;
+    unsigned short port;
+    char str[16];
+    char ip[4 * INET6_ADDRSTRLEN];
Why is ip 4*INET6_ADDRSTRLEN?

No idea really. I copied it from here (line 1821):
http://git.savannah.gnu.org/cgit/inetutils.git/tree/src/inetd.c
I'll do some digging about what kind of buffers Ncat uses to represent
IP's - if you know the answer already, I'd be happy to hear it.

There's a comment in inetd.c, according to which this
4*INET6_ADDRSTRLEN is a tradeoff between space and official max
hostname length (in their code, the buffer is susceptible to handle a
hostname too). I believe that INET6_ADDRSTRLEN is big enough in your
case, because you're requesting NI_NUMERICHOST and the getnameinfo
which is provided by nbase doesn't support IPv6... Why I'm insisting
on that is because this strange constant makes code hard to understand
("why 4 times something already larger than needed?"). I wouldn't want
that to end up being a line that noone dares touching, labeled with a
comment like: /* XXX: isn't this too big? */ :)

Finally, and way more important than sizing a buffer, please pay
attention to licensing issues. Nmap license isn't compatible with
GPLv3. I think BSD code is Ok (looks like this inetutils file has
both) but IIRC the BSD header has to be reproduced then. I let fyodor
or someone confirm but you might want to rewrite this code.

Regards

--
Henri

(sorry for replying twice, my GMail replied only to Henri by default)


Thanks for the warning, I'll pay more attention from now on. Though I
don't really believe that two variable declarations (out of which one
was altered already) and two calls is enough to void any license. It'd
be like patenting a set of getsockname/getnameinfo arguments.
Basically, only the following code is from inetd.c:

    char str[16];
    char ip[INET6_ADDRSTRLEN];

(...)

    if (getsockname (info->fd, (struct sockaddr *) &su, &alen) < 0) {
        bye("getsockname failed: %s",
socket_strerror(socket_errno()));
    }

    if (getnameinfo ((struct sockaddr *) &su, alen, ip, sizeof (ip),
            str, sizeof (str), NI_NUMERICHOST | NI_NUMERICSERV)==0) {
        _NCAT_SETENV("NCAT_LOCAL_ADDR", ip);
        _NCAT_SETENV("NCAT_LOCAL_PORT", str);
    } else {
        bye("getsockname failed: %s",
socket_strerror(socket_errno()));
    }

And consult its original:

  char ip[4 * INET6_ADDRSTRLEN];
  int ret;

(...)

  if (getsockname (ctrl, (struct sockaddr *) &sa_server, &len) < 0)
    syslog (LOG_WARNING, "getsockname(): %m");
  else
    {
      ret = getnameinfo ((struct sockaddr *) &sa_server, len,
                          ip, sizeof (ip), str, sizeof (str),
                          NI_NUMERICHOST | NI_NUMERICSERV);
      if (ret == 0)
        {
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