2 - Raspberry PI Community Projects

e confined. In any case, you will have to carefully review the generated rules and validate them
according to your knowledge of the application. Effectively, this approach tends to grant more
rights than are really required. The proper solution is often to create new types and to grant
rights on those types only. It also happens that a denied operation isn't fatal to the application,
in which case it might be better to just add a “dontaudit” rule to avoid the log entry despite the
effective denial.
COMPLEMENTS
No roles in policy rules
It might seem weird that roles do not appear at all when creating new rules.
SELinux uses only the domains to find out which operations are allowed. The
role intervenes only indirectly by allowing the user to switch to another domain.
SELinux is based on a theory known as Type Enforcement and the type
is the only element that maers when granting rights.
14.4.4.4. Compiling the Files
Once the 3 files (example.if, example.fc, and example.te) match your expectations for the
new rules, just run make to generate a module in the example.pp file (you can immediately
load it with semodule -i example.pp). If several modules are defined, make will create all the
corresponding .pp files.
14.5. Other Security-Related Considerations
Security is not just a technical problem; more than anything, it's about good practices and understanding
the risks. This section reviews some of the more common risks, as well as a few
best practices which should, depending on the case, increase security or lessen the impact of a
successful attack.
14.5.1. Inherent Risks of Web Applications
The universal character of web applications led to their proliferation. Several are often run
in parallel: a webmail, a wiki, some groupware system, forums, a photo gallery, a blog, and so
on. Many of those applications rely on the “LAMP” (Linux, Apache, MySQL, PHP) stack. Unfortunately,
many of those applications were also written without much consideration for security
problems. Data coming from outside is, too often, used with little or no validation. Providing
specially-crafted values can be used to subvert a call to a command so that another one is executed
instead. Many of the most obvious problems have been fixed as time has passed, but new
security problems pop up regularly.
VOCABULARY
SQL injection
When a program inserts data into SQL queries in an insecure manner, it becomes
vulnerable to SQL injections; this name covers the act of changing a
parameter in such a way that the actual query executed by the program is
different from the intended one, either to damage the database or to access
data that should normally not be accessible.
400 The Debian Administrator's Handbook