Leo's Notes - User contributions [en]

Patching a binary file with dd

2015-06-09T15:11:31Z

10.1.1.22:

Suppose I know an instruction in a particular offset after disassembling a binary file. You can use `dd` to change or patch a file like so.

dd if=nprobe bs=1 count=6 skip=$((0x1430C)) | xxd
6+0 records in
6+0 records out
6 bytes (6 B) copied, 0.000122275 s, 49.1 kB/s
0000000: 0f84 5401 0000 ..T...

I want to change the above from a jz to jnz like so:
echo "0F 85 54 01 00 00" | udcli -64 -x
0000000000000000 0f8554010000 jnz 0x15a

Overwrite the byte (or bytes) like so:
printf '\x0f\x85' | dd conv=notrunc of=nprobe bs=1 seek=$((0x1430C))
2+0 records in
2+0 records out
2 bytes (2 B) copied, 0.00097866 s, 2.0 kB/s

Verify:
[root@localhost bin]# dd if=nprobe bs=1 count=6 skip=$((0x1430C)) | xxd
6+0 records in
6+0 records out
6 bytes (6 B) copied, 0.000136555 s, 43.9 kB/s
0000000: 0f85 5401 0000 ..T...

To patch libnprobe so that it doesn't stop after 25000:
printf '\x0f\x85' | dd conv=notrunc of=/usr/local/lib/libnprobe-7.1.150608.so bs=1 seek=$((0x47e97))
dd if=/usr/local/lib/libnprobe-7.1.150608.so bs=1 count=6 skip=$((0x47e97)) | xxd
0000000: 0f85 d700 0000

This will effectively disable the limitation by always jumping regardless of the count.

Named

2015-03-24T04:57:19Z

10.1.1.22:

== Enable Query Logging ==

Use <code>rndc</code> to enable query logging:
rndc querylog on

Lookups will then be dumped into <code>/var/log/messages</code>

To see whether rndc querylog is enabled, run:

<syntaxhighlight lang="bash" line start="1" highlight="1" enclose="div">
rndc status
...
query logging is ON
...
server is up and running
</syntaxhighlight>

To enable logging by default, edit /etc/named.conf with:

<syntaxhighlight lang="bash" line start="1" enclose="div">
logging {
channel "querylog" {
file "/var/log/named-query.log";
print-time yes;
};
category queries { querylog; };
};
</syntaxhighlight>

== Disable IPv6 Lookups ==

If you have querylog enabled, you may see lots of messages like:

<syntaxhighlight lang="text" line start="1" enclose="div">
May 5 12:14:44 linux named[2492]: error (network unreachable) resolving 'ns2.google.com/A/IN': 2001:503:231d::2:30#53
May 5 12:14:44 linux named[2492]: error (network unreachable) resolving 'ns2.google.com/AAAA/IN': 2001:503:231d::2:30#53
May 5 12:14:44 linux named[2492]: error (network unreachable) resolving 'ns3.google.com/A/IN': 2001:503:231d::2:30#53
May 5 12:14:44 linux named[2492]: error (network unreachable) resolving 'ns4.google.com/A/IN': 2001:503:231d::2:30#53
May 5 12:14:44 linux named[2492]: error (network unreachable) resolving 'ns3.google.com/AAAA/IN': 2001:503:231d::2:30#53
May 5 12:14:44 linux named[2492]: error (network unreachable) resolving 'ns1.google.com/A/IN': 2001:503:231d::2:30#53
May 5 12:14:57 linux named[2492]: error (network unreachable) resolving 'ns2.p42.dynect.net/A/IN': 2001:500:3::42#53
</syntaxhighlight>

Since I don't have IPv6 on my network, it's obvious why I can't lookup IPv6 addresses. To fix this, do:

<syntaxhighlight lang="bash" line start="1" enclose="div">
vi /etc/sysconfig/named
OPTIONS="-4"
</syntaxhighlight>

== Creating 'zones' via Views ==

If you want to provide a set of IP addresses or subnets with a specific set of zones, use <code>view</code>s to accomplish this. The basic syntax for a view is:

<syntaxhighlight lang="text">
view "NetworkAB" {
match-clients { subnetA; subnetB; };

# Zones go here
};
</syntaxhighlight>

You may also use <code>acl</code> to group multiple subnets into one 'client'.

<syntaxhighlight lang="text">
acl subnetAB { subnetA; subnetB; };

view "NetworkAB" {
match-clients { subnetAB; };

# Zones go here
};
</syntaxhighlight>

To have one specific IP address inside another view instead, use the <code>!</code> operator in either the ACL definition list or the <code>match-clients</code> list.

<syntaxhighlight lang="text">
acl subnetAB { ! leosIPInSubnetA/32; subnetA; subnetB; };
acl subnetLeo { leosIPInSubnetA/32; };

view "NetworkAB" {
match-clients { subnetAB; };

# Zones go here
};

view "LeosView" {
match-clients { subnetLeo; };

# Zones only Leo can see can go here
}
</syntaxhighlight>

[[Category:Linux]]
[[Category:Services]]

Webcam

2015-03-24T03:07:57Z

10.1.1.22:

== Linux ==
To get a webcam working for Linux, ensure that it's supported. Newer webcams tend to have support though cheaper non-HD webcams from China might not. You should see a <code>/dev/video0</code> device when the webcam is plugged into the computer. If not, check <code>dmesg</code> and see if the USB device is being detected. <code>lsusb</code> should also list it.

The default permissions set to <code>/dev/video0</code> is set by udev. If you need to change the device permissions (say making it world read/writable), you will need to create a udev rule by creating a new file in <code>/etc/udev/rules.d/</code> with the following contents:

<syntaxhighlight lang="text">
SUBSYSTEM=="video4linux", BUS=="usb", SYSFS{idVendor}=="045e", SYSFS{idProduct}=="0761", NAME="video0", MODE="0666"
</syntaxhighlight>

The Vendor ID and product ID must match the values from <code>lsusb</code>. For the example above (a Microsoft LifeCam VX-2000):
# lsusb
Bus 001 Device 005: ID 045e:0761 Microsoft Corp.

To capture images, use any one of the following utilities:
* fswebcam
* uvccapture

You may configure the webcam settings using <code>v4l-utils</code>. See http://www.techytalk.info/webcam-settings-control-ubuntu-fedora-linux-operating-system-cli/

=== fswebcam ===
fswebcam -r 640x480 --jpeg 85 -D 1 web-cam-shot.jpg

==== Dumping fswebcam images via HTTP ====
You can make a quick an dirty wrapper around the command above so that it can be viewed via the web.

<syntaxhighlight lang="php">
<?php

system("fswebcam -r 640x480 --jpeg 85 -D 1 /tmp/out.jpg > /dev/null");
header("Content-Type: image/jpeg");
echo file_get_contents("/tmp/out.jpg");
</syntaxhighlight>

=== uvccapture ===

[[Category:Linux]]