When '-sandbox on,spawn=deny' is given, we are supposed to block the
ability to spawn processes. We naively blocked the 'fork' syscall,
forgetting that any modern libc will use the 'clone' syscall instead.
We can't simply block the 'clone' syscall though, as that will break
thread creation. We thus list the set of flags used to create threads
and block anything that doesn't match this exactly.
Acked-by: Eduardo Otubo <otubo@redhat.com>
Signed-off-by: Daniel P. Berrangé <berrange@redhat.com>
The handling of some syscalls / libc function is quite subtle. For
example, 'fork' at a libc level doesn't always correspond to 'fork'
at a syscall level, since the 'clone' syscall is preferred usually.
The unit test will help to detect these kind of problems. A point of
difficulty in writing a test though is that the QEMU build process may
already be confined by seccomp. For example, if running inside a
container. Since we can't predict what filtering might have been applied
already, we are quite conservative and skip all tests if we see any kind
of seccomp filter active.
Acked-by: Eduardo Otubo <otubo@redhat.com>
Signed-off-by: Daniel P. Berrangé <berrange@redhat.com>
