Kir Kolyshkin
87bd784614
Add a workaround for a problem of older container-selinux not allowing runc to use dmz feature. If runc sees that SELinux is in enforced mode and the container's SELinux label is set, it disables dmz. Add a build tag, runc_dmz_selinux_nocompat, which disables the workaround. Newer distros that ship container-selinux >= 2.224.0 (currently CentOS Stream 8 and 9, RHEL 8 and 9, and Fedora 38+) may build runc with this build tag set to benefit from dmz working with SELinux. Document the build tag in the top-level and libct/dmz READMEs. Use the build tag in our CI builds for CentOS Stream 9 and Fedora 38, as they already has container-selinux 2.224.0 available in updates. Add a TODO to use the build tag for CentOS Stream 8 once it has container-selinux updated. Signed-off-by: Kir Kolyshkin <kolyshkin@gmail.com>
1.4 KiB
Runc-dmz
runc-dmz is a small and very simple binary used to execute the container's entrypoint.
Making it small
To make it small we use the Linux kernel's nolibc include files, so we don't use the libc.
A full cp of it is here in nolibc/, but removing the Makefile that is GPL. DO NOT FORGET to
remove the GPL code if updating the nolibc/ directory.
The current version in that folder is from Linux 6.6-rc3 tag (556fb7131e03b0283672fb40f6dc2d151752aaa7).
It also support all the architectures we support in runc.
If the GOARCH we use for compiling doesn't support nolibc, it fallbacks to using the C stdlib.
SELinux compatibility issue and a workaround
Older SELinux policy can prevent runc to execute the dmz binary. The issue is fixed in container-selinux v2.224.0. Yet, some older distributions may not have the fix, so runc has a runtime workaround of disabling dmz if it finds that SELinux is in enforced mode and the container SELinux label is set.
Distributions that have a sufficiently new container-selinux can disable the
workaround by building runc with the runc_dmz_selinux_nocompat build flag,
essentially allowing dmz to be used together with SELinux.