SELinux users might be facing failures when emerge is merging a package to the file system, with an error that looks like so:

>>> Setting SELinux security labels
/usr/lib64/portage/bin/ line 1112: 23719 Segmentation fault      /usr/sbin/setfiles "${file_contexts_path}" -r "${D}" "${D}"
 * ERROR: dev-libs/libpcre-8.35::gentoo failed:
 *   Failed to set SELinux security labels.

This has been reported as bug 516608 and, after some investigation, the cause is found. First the quick workaround:

~# cd /etc/selinux/strict/contexts/files
~# rm *.bin

And do the same for the other SELinux policy stores on the system (targeted, mcs, mls, ...).

Now, what is happening... Inside the mentioned directory, binary files exist such as file_contexts.bin. These files contain the compiled regular expressions of the non-binary files (like file_contexts). By using the precompiled versions, regular expression matching by the SELinux utilities is a lot faster. Not that it is massively slow otherwise, but it is a nice speed improvement nonetheless.

However, when pcre updates occur, then the basic structures that pcre uses internally might change. For instance, a number might switch from a signed integer to an unsigned integer. As pcre is meant to be used within the same application run, most applications do not have any issues with such changes. However, the SELinux utilities effectively serialize these structures and later read them back in. If the new pcre uses a changed structure, then the read-in structures are incompatible and even corrupt.

Hence the segmentation faults.

To resolve this, Stephen Smalley created a patch that includes PCRE version checking. This patch is now included in sys-libs/libselinux version 2.3-r1. The package also recompiles the existing *.bin files so that the older binary files are no longer on the system. But there is a significant chance that this update will not trickle down to the users in time, so the workaround might be needed.

I considered updating the pcre ebuilds as well with this workaround, but considering that libselinux is most likely to be stabilized faster than any libpcre bump I let it go.

At least we have a solution for future upgrades; sorry for the noise.

Edit: libselinux-2.2.2-r5 also has the fix included.


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