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dev-manual: Updates to the "Making Images More Secure" section. 

Fixes [YOCTO #5482]

Applied extensive review edist from Paul Eggleton throughout
this section.

(From yocto-docs rev: aa0bcd9199c83b43bad2390ff2292a8c2abe7455)

Signed-off-by: Scott Rifenbark <scott.m.rifenbark@intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>
This commit is contained in:
Scott Rifenbark 2014-05-30 17:09:05 +03:00 committed by Richard Purdie
parent 8beca348c1
commit 5d14f3c03a
1 changed files with 92 additions and 28 deletions
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120
documentation/dev-manual/dev-manual-common-tasks.xml
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@ -3841,14 +3841,46 @@
<title>Making Images More Secure</title>
<para>
If securing your image is of concern, there are steps, tools,
Security for a device is always a concern.
Consider the issues and problems discussed in just this
sampling of work found across the Internet:
<itemizedlist>
<listitem><para><emphasis>
"<ulink url='https://www.schneier.com/blog/archives/2014/01/security_risks_9.html'>Security Risks of Embedded Systems</ulink>"</emphasis>
by Bruce Schneier
</para></listitem>
<listitem><para><emphasis>
"<ulink url='http://internetcensus2012.bitbucket.org/paper.html'>Internet Census 2012</ulink>"</emphasis>
by Carna Botnet</para></listitem>
<listitem><para><emphasis>
"<ulink url='http://elinux.org/images/6/6f/Security-issues.pdf'>Security Issues for Embedded Devices</ulink>"</emphasis>
by Jake Edge
</para></listitem>
<listitem><para><emphasis>
"<ulink url='https://www.nccgroup.com/media/18475/exploiting_security_gateways_via_their_web_interfaces.pdf'>They ought to know better: Exploiting Security
Gateways via their Web Interfaces</ulink>"</emphasis>
by Ben Williams
</para></listitem>
</itemizedlist>
</para>
<para>
When securing your image is of concern, there are steps, tools,
and variables that you can consider to help you reach the
security goals you need for your particular device.
Not all situations are identical when it comes to making an
image secure.
Consequently, this section provides some guidance and suggestions
for consideration when you want to make your image more secure.
The section does not offer a complete solution.
</para>
<para>
Because the security requirements and risks are
different for every type of device, this section cannot
provide a complete reference on securing your custom OS.
It is strongly recommended that you also consult other sources
of information on embedded Linux system hardening and on
security.
</para>
<section id='general-considerations'>
@ -3895,7 +3927,10 @@
<listitem><para>
Ensure you remove or disable debugging functionality
before producing the final image.
</para></listitem>
For information on how to do this, see the
"<link linkend='considerations-specific-to-the-openembedded-build-system'>Considerations Specific to the OpenEmbedded Build System</link>
section.
</para></listitem>
<listitem><para>
Ensure you have no network services listening that
are not needed.
@ -3929,6 +3964,7 @@
</para>
<para>
<!--
The GCC/LD flags in <filename>security_flags.inc</filename>
enable more secure code generation.
By including the <filename>security_flags.inc</filename>
@ -3938,10 +3974,11 @@
The GCC/LD flags are enabled by default in the
<filename>poky-lsb</filename> distribution.
</note>
-->
Use the following line in your
<filename>local.conf</filename> file
to enable the security compiler and
linker flags to your build:
<filename>local.conf</filename> file or in your custom
distribution configuration file to enable the security
compiler and linker flags to your build:
<literallayout class='monospaced'>
require conf/distro/include/security_flags.inc
</literallayout>
@ -3966,38 +4003,65 @@
sure that it does not have "debug-tweaks" before
producing your final image.
Among other things, leaving this in place sets the
root password as blank.
root password as blank, which makes logging in for
debugging or inspection easy during
development but also means anyone can easily log in
during production.
</para></listitem>
<listitem><para>
It is possible to set a root password for the image.
For information on how to do that, see the
<ulink url='https://wiki.yoctoproject.org/wiki/FAQ:How_do_I_set_or_change_the_root_password'>How do I set or change the root password</ulink>
Wiki page.
When you set up root passwords for multiple images,
you should not duplicate them.
See the note on passwords at the end of this list.
</para>
<para>
To set up a root password,
use the <filename>extrausers</filename>
class, which is the preferred method.
For an example on how to set up the root password,
see the
"<ulink url='&YOCTO_DOCS_REF_URL;#ref-classes-extrausers'><filename>extrausers.bbclass</filename></ulink>"
section.
<note>
You can also see the the example in the
<ulink url='https://wiki.yoctoproject.org/wiki/FAQ:How_do_I_set_or_change_the_root_password'>How do I set or change the root password Wiki</ulink>
page as an alternative method.
</note>
</para></listitem>
<listitem><para>
It is possible to add an additional user account
for later administrative or service access using the
<ulink url='&YOCTO_DOCS_REF_URL;#ref-classes-extrausers'><filename>extrausers</filename></ulink>
class or the
<ulink url='&YOCTO_DOCS_REF_URL;#var-ROOTFS_POSTPROCESS_COMMAND'><filename>ROOTFS_POSTPROCESS_COMMAND</filename></ulink>
variable.
For an example on how to add users, see the
"<ulink url='&YOCTO_DOCS_REF_URL;#ref-classes-extrausers'><filename>extrausers.bbclass</filename></ulink>"
section.
for later administrative or service access.
As with root passwords, be sure to not duplicate
passwords for generic users (e.g. tester, qa, and
so forth) across multiple devices.
See the note on passwords following this list.
</para>
<para>If you do add extra user accounts,
be cautious about setting
the same password for every device.
If you want the device to remain secure
from unauthorized access, and the password set on
all devices becomes compromised, then every device
becomes compromised.
If you need this access but want to ensure security,
consider setting a different, random password for each
device.
<para>
As with the root password, you also use the
<ulink url='&YOCTO_DOCS_REF_URL;#ref-classes-extrausers'><filename>extrausers</filename></ulink>
class.
</para></listitem>
<listitem><para>
Consider enabling a Mandatory Access Control (MAC)
framework (such as SMACK or SELinux) and tuning it
appropriately for your device's usage.
</para></listitem>
</itemizedlist>
</para>
<para>
<note><title>A Note about Passwords</title>
When adding extra user accounts or deciding on root
passwords for multiple devices, be cautious about setting
the same passwords for multiple users or devices.
If you want the device to remain secure from unauthorized
access, and the password set on all devices becomes
compromised, then every device becomes compromised.
If you need this access but want to ensure security,
consider setting a different, random passwords for each
user or device.
</note>
</para>
</section>
<section id='tools-for-hardening-your-image'>