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<center>
<h3>The Honeypot procfs</h3>
</center>
hppfs reads a proc hierarchy in the current working directory
on the host of the UML. When a UML process accesses a /proc entry,
hppfs consults the corresponding entry in this hierarchy to decide what
to do. This entry is a directory which contains a file which
describes what to do with that entry. The possibilities are as
follows:
<ul>
<li>
No entry on the host - hppfs passes the operation on to the UML /proc
- effectively this means that entry is unmodified. Most /proc entries
contain no information about whether the machine is a UML, so these
can be left alone.
</li>
<li>
The host entry is a normal file or symlink - the contents of this file
(or target of the link) will replace the UML /proc entry. This is
appropriate for /proc entries, such as /proc/cmdline, which can be
replaced by the corresponding /proc entry on the host. It is also
appropriate for entries which must be changed, but which are static.
In this case, you'd drop the static file into the host proc hierarchy
for that UML.
</li>
<li>
The host entry is a directory and contains
<ul>
<li>
"remove" (a normal file) - this causes the entry to disappear from the
UML /proc. This can be used to remove things which don't exist on
physical machines, such as /proc/exitcode and /proc/mconsole.
</li>
<li>
"r" (a unix socket) - this causes the entry to be generated on
demand by the process attached to the socket. This is useful for
entries which must be dynamically generated, but can be generated from
scratch on the host.
</li>
<li>
"rw" (a unix socket) - this is similar to "r", except that the current
UML /proc contents of that entry are written to the socket before the
new contents are read. This allows the host process to filter the UML
/proc data. This is useful when data must be removed from a UML /proc
entry.
</li>
</ul>
</li>
</ul>
The files inside /proc/<i>pid</i> need slightly special handling
because you can't know on the host what pids are going to be present
inside UML. UML looks in the pid subdirectory of the host's shadow
proc for all modifications of UML /proc/<i>pid</i> entries.
<p>
The uml_utilities tarball (under honeypot/) contains a few things to
simplify the disguising of a UML's /proc:
<ul>
<li>
hppfs.pm - A perl module which acts as a server for any dynamic proc
entries that need to be generated.
</li>
<li>
hppfslib.pm - A library which contains a set of utilities for
constructing a fake proc environment.
</li>
<li>
honeypot.pl - A sample driver for hppfs.pm and hppfslib.pm which
overrides a number of UML /proc entries in various ways.
</li>
</ul>
<a name="Example"/><table width="100%" bgcolor="#e0e0e0">
<tr>
<td>
<b>
<font color="black">Example</font>
</b>
</td>
</tr>
</table>
<blockquote head="Example">
Here is an example of setting up a customized UML /proc using hppfs.
<p>
First, boot a UML with hppfs enabled ('grep hppfs /proc/filesystems'
to check). Login in and mount hppfs over /proc:
<blockquote>
<tt>
<font color="#000000" where="UML">UML# mount none /proc -t hppfs</font>
</tt>
</blockquote>
ls /proc and notice that it doesn't seem any different than before:
<tt>
<pre>
<font size="-1">
usermode:~# ls /proc
1 130 137 7 devices interrupts loadavg mtd swaps
100 131 140 8 dma iomem locks net sys
104 132 2 93 driver ioports meminfo partitions sysvipc
109 133 3 95 execdomains irq misc scsi tty
121 134 4 bus exitcode kcore mm self uptime
126 135 5 cmdline filesystems kmsg modules slabinfo version
129 136 6 cpuinfo fs ksyms mounts stat
</font>
</pre>
</tt>
Create a proc directory in the current working directory of the UML
<blockquote>
<tt>
<font color="#000000" where="host">host% mkdir proc</font>
</tt>
</blockquote>
Now, put something into proc/cmdline
<blockquote>
<tt>
<font color="#000000" where="host">host% echo 'hi there' > proc/cmdline</font>
</tt>
</blockquote>
and look at the UML's /proc/cmdline
<tt>
<pre>
<font size="-1">
usermode#~: cat /proc/cmdline
hi there
</font>
</pre>
</tt>
This should give you a good idea of how to make simple modifications
to the UML's /proc. A more realistic example would be to make
/proc/cmdline the same as on the host. You can do this by copying the
host's /proc/cmdline into proc, but a symbolic link will work, too:
<blockquote>
<tt>
<font color="#000000" where="host">host% ln -s /proc/cmdline proc/cmdline</font>
</tt>
</blockquote>
<tt>
<pre>
<font size="-1">
usermode:~# cat /proc/cmdline
auto BOOT_IMAGE=2.4.19 ro root=306 BOOT_FILE=/boot/vmlinuz
</font>
</pre>
</tt>
With that step, you removed one way for an intruder to fingerprint the
machine as a UML. There are a bunch of others, and it would be nice
to automate the creation of realistic, fake data for them as well.
<p>
Grab the uml_utilities tarball, unpack it, and cd into honeypot/. Run
honeypot.pl with the current directory of UML as an argument:
<blockquote>
<tt>
<font color="#000000" where="host">host% perl ./honeypot.pl ~/linux/2.4/um/</font>
</tt>
</blockquote>
honeypot.pl asks the hppfs module to
<ul>
<li>
create the directory:
<tt>
<pre>
<font size="-1">
my $hppfs = hppfs->new($dir);
</font>
</pre>
</tt>
</li>
<li>
initialize its contents:
<tt>
<pre>
<font size="-1">
$hppfs->add("devices" => remove_line("ubd"),
"uptime" => proc("uptime"),
"exitcode" => "remove",
"filesystems" => remove_line("hppfs"),
"interrupts" => proc("interrupts"),
"iomem" => proc("iomem"),
"ioports" => proc("ioports"),
"mounts" => remove_line("hppfs"),
"pid/mounts" => remove_line("hppfs"),
"version" => proc("version") );
</font>
</pre>
</tt>
</li>
<li>
call the hppfs server main loop, which will service requests from the
hppfs client inside UML for dynamic proc entries:
<tt>
<pre>
<font size="-1">
$hppfs->handler();
</font>
</pre>
</tt>
</li>
</ul>
If you look at the proc directory now, you will see a bunch of new
entries:
<tt>
<pre>
<font size="-1">
host% ls ~/linux/2.4/um/proc/
devices filesystems iomem mounts uptime
exitcode interrupts ioports pid version
</font>
</pre>
</tt>
These all need some sort of manipulation.
<ul>
<li>
Removal - /proc/exitcode is specific to UML; writing to it allows the
exit code of UML on the host to be changed. This obviously can't be
present in a honeypot, so the argument
<blockquote>
<tt>
<font color="#000000"> "exitcode" => "remove",</font>
</tt>
</blockquote>
to hppfs::add causes it to create an exitcode directory in proc on the
host:
<tt>
<pre>
<font size="-1">
host% ls -al ~/linux/2.4/um/proc/exitcode
total 8
drwxrw-rw- 2 jdike jdike 4096 Dec 18 14:43 .
drwxrw-rw- 11 jdike jdike 4096 Dec 18 14:43 ..
-rw-rw-rw- 1 jdike jdike 0 Dec 18 14:43 remove
</font>
</pre>
</tt>
The 'remove' entry tells hppfs to hide the UML /proc 'exitcode' file,
and 'ls /proc' inside the UML shows that it is indeed gone.
</li>
<li>
Fabrication - we've already seen an example of fabricating a proc
entry from scratch. Dropping a static file into proc will cause it to
replace the corresponding UML /proc entry. However, lots of /proc
files are dynamic, so looking at it twice and seeing exactly the same
data would be a tip-off that something's wrong. If the host's /proc
entry is usable, then a symbolic link from the shadow proc to /proc
will be fine. This is what these arguments to hppfs::add do:
<tt>
<pre>
<font size="-1">
"uptime" => proc("uptime"),
"interrupts" => proc("interrupts"),
"iomem" => proc("iomem"),
"ioports" => proc("ioports"),
"mounts" => remove_line("hppfs"),
"pid/mounts" => remove_line("hppfs"),
"version" => proc("version") );
</font>
</pre>
</tt>
</li>
(although the actual hppfslib implementation of proc() currently has
the hppfs server execute 'cat /proc/<file>')
<li>
Filtering - sometimes the host's /proc or anything else we can
generate on the host won't be right. Instead, we might want to take
the UML /proc file contents and manipulate them somehow. An example
is /proc/filesystems. In this honeypot, it contains an entry for
hppfs, which can't be allowed to remain. So, this argument to
hppfs::add causes that one line to be removed, leaving everything else
the same:
<tt>
<pre>
<font size="-1">
"filesystems" => remove_line("hppfs"),
</font>
</pre>
</tt>
</li>
<li>
Note the "pid/mounts" entry. That covers all references to any
/proc/<i>pid</i>/mounts file inside UML.
</li>
</ul>
</blockquote>
</td>
</tr>
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