Prevent container-inits from using CLONE_PARENT If a container-init creates a sibling (using CLONE_PARENT), pid namespace semantics become complicated: - the "active pid namespace" of the sibling will be the descendant container, but its not obvious if that is correct. - if container-init exits, it will terminate the sibling, but again its not clear if that is the correct behavior. - the sibling exists in both parent and child containers while current pid namespace semantics assume that only container-init can exist in both parent/child containers. - the parent of the sibling is not a descendant of container-init (while pid namespaces assume that all processes in the container are descendants of the container-init) - When the sibling dies, the SIGCHLD is sent to its parent (if alive), i.e the signal escapes the container to a parent container. (if the parent of the sibling exits, the container-init then becomes the reaper of the sibling). To keep pid namespace semantics simple, prevent container-inits from using CLONE_PARENT at least until we have a better understanding of CLONE_PARENT and pid-namespace interactions. Untested, RFC patch :-) Signed-off-by: Sukadev Bhattiprolu <sukadev@xxxxxxxxxx> --- kernel/fork.c | 8 ++++++++ 1 file changed, 8 insertions(+) Index: linux-mmotm/kernel/fork.c =================================================================== --- linux-mmotm.orig/kernel/fork.c 2009-06-17 18:23:23.000000000 -0700 +++ linux-mmotm/kernel/fork.c 2009-06-17 19:17:54.000000000 -0700 @@ -974,6 +974,14 @@ static struct task_struct *copy_process( if ((clone_flags & CLONE_SIGHAND) && !(clone_flags & CLONE_VM)) return ERR_PTR(-EINVAL); + /* + * To keep pid namespace semantics simple, prevent container-inits + * from creating siblings. + */ + if ((clone_flags & CLONE_PARENT) && + is_container_init(current) && !is_global_init(current)) + return ERR_PTR(-EINVAL); + retval = security_task_create(clone_flags); if (retval) goto fork_out; _______________________________________________ Containers mailing list Containers@xxxxxxxxxxxxxxxxxxxxxxxxxx https://lists.linux-foundation.org/mailman/listinfo/containers
