This function will be called if libvirtd was restarted while some
domains were running. It will try to detect existing programs attached
to the guest cgroup.
Signed-off-by: Pavel Hrdina <phrdina@redhat.com>
Reviewed-by: Ján Tomko <jtomko@redhat.com>
This function loads the BPF prog with prepared map into kernel and
attaches it into guest cgroup. It can be also used to replace existing
program in the cgroup if we need to resize BPF map to store more rules
for devices. The old program will be closed and removed from kernel.
There are two possible ways how to create BPF program:
- One way is to write simple C-like code which can by compiled into
BPF object file which can be loaded into kernel using elfutils.
- The second way is to define macros which look like assembler
instructions and can be used directly to create BPF program that
can be directly loaded into kernel.
Since the program is not too complex we can use the second option.
If there is no program, all devices are allowed, if there is some
program it is executed and based on the exit status the access is
denied for 0 and allowed for 1.
Our program will follow these rules:
- first it will try to look for the specific key using major and
minor to see if there is any rule for that specific device
- if there is no specific rule it will try to look for any rule that
matches only major of the device
- if there is no match with major it will try the same but with
minor of the device
- as the last attempt it will try to look for rule for all devices
and if there is no match it will return 0 to deny that access
Signed-off-by: Pavel Hrdina <phrdina@redhat.com>
Reviewed-by: Ján Tomko <jtomko@redhat.com>
There is no exact way how to figure out whether BPF devices support is
compiled into kernel. One way is to check kernel configure options but
this is not reliable as it may not be available. Let's try to do
syscall to which will list BPF cgroup device programs.
Signed-off-by: Pavel Hrdina <phrdina@redhat.com>
Reviewed-by: Ján Tomko <jtomko@redhat.com>
