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The existing virSecurityManagerSetProcessLabel() API is designed so that it must be called after forking the child process, but before exec'ing the child. Due to the way the virCommand API works, that means it needs to be put in a "hook" function that virCommand is told to call out to at that time. Setting the child process label is a basic enough need when executing any process that virCommand should have a method of doing that. But virCommand must be told what label to set, and only the security driver knows the answer to that question. The new virSecurityManagerSet*Child*ProcessLabel() API is the way to transfer the knowledge about what label to set from the security driver to the virCommand object. It is given a virCommandPtr, and each security driver calls the appropriate virCommand* API to tell virCommand what to do between fork and exec. 1) in the case of the DAC security driver, it calls virCommandSetUID/GID() to set a uid and gid that must be set for the child process. 2) for the SELinux security driver, it calls virCommandSetSELinuxLabel() to save a copy of the char* that will be sent to setexeccon_raw() *after forking the child process*. 3) for the AppArmor security drivers, it calls virCommandSetAppArmorProfile() to save a copy of the char* that will be sent to aa_change_profile() *after forking the child process*. With this new API in place, we will be able to remove virSecurityManagerSetProcessLabel() from any virCommand pre-exec hooks. (Unfortunately, the LXC driver uses clone() rather than virCommand, so it can't take advantage of this new security driver API, meaning that we need to keep around the older virSecurityManagerSetProcessLabel(), at least for now.)
LibVirt : simple API for virtualization
Libvirt is a C toolkit to interact with the virtualization capabilities
of recent versions of Linux (and other OSes). It is free software
available under the GNU Lesser General Public License. Virtualization of
the Linux Operating System means the ability to run multiple instances of
Operating Systems concurrently on a single hardware system where the basic
resources are driven by a Linux instance. The library aim at providing
long term stable C API initially for the Xen paravirtualization but
should be able to integrate other virtualization mechanisms if needed.
Daniel Veillard <veillard@redhat.com>