Each new release of Red Hat® Enterprise Linux® is not only built on top of the previous version, but a large number of its components incorporate development from the Fedora distribution. For Red Hat Enterprise Linux 7, most components are aligned with Fedora 19, and with select components coming from Fedora 20. This means that users benefit from new development in Fedora, such as firewalld which is described below. While preparing the next release of Red Hat Enterprise Linux, we review components for their readiness for an enterprise-class distribution. We also make sure that we address known vulnerabilities before the initial release. And we review new components to check that they meet our standards regarding security and general suitability for enterprise use.

One of the first things that happens is a review of the material going into a new version of Red Hat Enterprise Linux. Each release includes new packages that Red Hat has never shipped before and anything that has never been shipped in a Red Hat product receives a security review. We look for various problems – from security bugs in the actual software to packaging issues. It’s even possible that some packages won’t make the cut if they prove to have issues that cannot be resolved in a manner we decide is acceptable. It’s also possible that a package was once included as a dependency or feature that is no longer planned for the release. Rather than leave those in the release, we do our best to remove the unneeded packages as they could result in security problems later down the road.

Previously fixed security issues are also reviewed to ensure nothing has been missed since the last version. While uncommon, it is possible that a security fix didn’t make it upstream, or was somehow dropped from a package at some point during the move between major releases. We spend time reviewing these to ensure nothing important was missed that could create problems later.

Red Hat Product Security also adds several new security features in order to better protect the system.

Before its 2011 revision, the C++ language definition was ambiguous as to what should happen if an integer overflow occurs during the size computation of an array allocation. The C++ compiler in Red Hat Enterprise Linux 7 will perform a size check (and throw std::bad_alloc on failure) if the size (in bytes) of the allocated array exceeds the width of a register, even in C++98 mode. This change affects the code generated by the compiler–it is not a library-level correction. Consequently, we compiled all of Red Hat Enterprise Linux 7 with a compiler version that performs this additional check.

When we compiled Red Hat Enterprise Linux 7, we also tuned the compiler to add “stack protector” instrumentation to additional functions. The GCC compiler in Red Hat Enterprise Linux 6 used heuristics to determine whether a function warrants “stack protector” instrumentation. In contrast, the compiler in Red Hat Enterprise Linux 7 uses precise rules that add the instrumentation to only those functions that need it. This allowed us to instrument additional functions with minimal performance impact, extending this probabilistic defense against stack-based buffer overflows to an even larger part of the code base.

Red Hat Enterprise Linux 7 also includes firewalld. firewalld allows for centralized firewall management using high-level concepts, such as zones. It also extends spoofing protection based on reverse path filters to IPv6, where previous Red Hat Enterprise Linux versions only applied anti-spoofing filter rules to IPv4 network traffic.

Every version of Red Hat Enterprise Linux is the result of countless hours of work from many individuals. Above we highlighted a few of the efforts that the Red Hat Product Security team assisted with in the release of Red Hat Enterprise Linux 7. We also worked with a number of other individuals to see these changes become reality. Our job doesn’t stop there, though. Once Red Hat Enterprise Linux 7 was released, we immediately began tracking new security issues and deciding how to fix them. We’ll further explain that process in an upcoming blog post about fixing security issues in Red Hat Enterprise Linux 7.