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<erl>
out(A) ->
{ssi, "TAB.inc", "%%",[{"privbind", "choosen"}]}.
</erl>
<div id="entry">
<h1>Binding to privileged ports</h1>
<p>
A common misfeature found on UN*X operating systems is the
restriction that only root can bind to ports below 1024.
Many a dollar has been wasted on workarounds and -often- the results are
security holes.
</p>
<p>
Both FreeBSD and Solaris have elegant configuration options to
turn this feature off. On FreeBSD:
<div class="box">
<verbatim>
$ sysctl net.inet.ip.portrange.reservedhigh=0
</verbatim>
</div>
the above is best added to your /etc/sysctl.conf
</p>
<p>
Similarly on Solaris we can just configure away this misfeature.
Assuming we want to run Yaws/SSL under a non-root user "erlang" on
ports 80/443.
</p>
<p>
On Solaris we can do that easily by granting the specific right to bind
privileged ports <1024 (and only that) to "erlang" using:
</p>
<div class="box">
<verbatim>
$ /usr/sbin/usermod -K defaultpriv=basic,net_privaddr erlang
</verbatim>
</div>
<p>
And check the we get what we want through:
</p>
<div class="box">
<verbatim>
$ grep erlang /etc/user_attr
erlang::::type=normal;defaultpriv=basic,net_privaddr
</verbatim>
</div>
<p>
On Linux, kernels later than 2.6.24, it's possible to do:
</p>
<div class="box">
<verbatim>
$ setcap 'cap_net_bind_service=+ep' /usr/lib/erlang/erts-5.7.4/bin/beam
</verbatim>
</div>
<p>
The above command grants the capability of binding
privileged ports to beam. Note, you have to grant the priviliges to the
actual exectuable you are using.
<p>
<p>
There are a couple
of other options on Linux. One is to use an auxiliary program
like authbind <em>http://packages.debian.org/stable/authbind</em>
or privbind <em>http://sourceforge.net/projects/privbind/</em>
</p>
<p>
These programs are run by root. Yaws writes its temporary
JIT compiled files in $HOME/.yaws and this doesn't work that
well with authbind/privbind. A non root user will try to
write in /root/.yaws. The solution to this is to set the
environment variable YAWSHOME. Yaws will then consider that to
be HOME rather that $HOME.
</p>
<p>
To start yaws under e.g authbind we can do:
</p>
<div class="box">
<verbatim>
$ sudo YAWSHOME=/tmp/abc privbind -u klacke /home/klacke/bin/yaws \
-c /home/klacke/yaws.conf -i
</verbatim>
</div>
<p>
The above command starts yaws as user <em>klacke</em> and bind
to ports below 1024
</p>
<p>
Yet another option is to is to install fdsrv which is a standalone
program that has the suid bit set, binds privileged ports and passes
the filedescriptor to yaws. I have made a package out of the jungerl
code that can be easily installed just through the usual cycle of
make && make install The code is at
</p>
<pre>
http://yaws.hyber.org/download/fd_server-2.3.0.tgz
</pre>
<p>
One major drawback with fdsrv is that it doesn't work for SSL. With
the case of SSL, one possible solution is to put ssltunnel in
front of yaws and let yaws bind to 127.0.0.1
</p>
<p>
All in all the fdsrv option is much worse that the authbind option.
</p>
<p>
Here is a description on how to do this on MacOs X. It's not exactly the same,
since we're still binding to non privileged ports. However,
edit /etc/sysctl and add:
</p>
<pre>
net.inet.ip.forwarding=1
</pre>
<p>
Then with ipfw as the firewall (turn off the gui firewall in system
preferences and manage own rules) use the ipfw rules like these - for
testing on your own box use something like:
</p>
<pre>
ipfw add fwd 127.0.0.1,8080 tcp from any to 127.0.0.1 dst-port 80 in
ipfw add fwd 127.0.0.1,8443 tcp from any to 127.0.0.1 dst-port 443 in
</pre>
<p>
set up yaws to use 8080 and 8443 in yaws.conf and then run as some non
root user. When you browse to http://127.0.0.1 or https://127.0.0.1
you will see your pages that are actually on 8080 and 8443 internally
but will be forwarded via ipfw forwarding.
</p>
<p>
Yet another (more complicated way) for linux users is to hack the kernel.
Here is a patch I did for some version of the 2.6 series kernels .. you get the idea.
</p>
<verbatim>
[root@lax]ipv4 > diff -c af_inet.c*
*** af_inet.c Wed Feb 23 23:31:35 2005
--- af_inet.c~ Thu Feb 17 18:13:13 2005
***************
*** 423,434 ****
snum = ntohs(addr->sin_port);
err = -EACCES;
- #if 0
- /* removed by klacke */
if (snum && snum < PROT_SOCK && !capable(CAP_NET_BIND_SERVICE))
goto out;
- #endif
-
/* We keep a pair of addresses. rcv_saddr is the one
* used by hash lookups, and saddr is used for transmit.
--- 423,430 ----
</verbatim>
<erl>
out(A) -> {ssi, "END2",[],[]}.
</erl>
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