fork(): disable CLONE_PARENT for init

When global or container-init processes use CLONE_PARENT, they create a
multi-rooted process tree.  Besides siblings of global init remain as
zombies on exit since they are not reaped by their parent (swapper).  So
prevent global and container-inits from creating siblings.

Signed-off-by: Sukadev Bhattiprolu <sukadev@us.ibm.com>
Acked-by: Eric W. Biederman <ebiederm@xmission.com>
Acked-by: Roland McGrath <roland@redhat.com>
Cc: Oren Laadan <orenl@cs.columbia.edu>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Serge Hallyn <serue@us.ibm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 10 insertions, 0 deletions

diff --git a/kernel/fork.c b/kernel/fork.c
index 51ad0b0b7266..b51fd2ccb2f1 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -979,6 +979,16 @@ static struct task_struct *copy_process(unsigned long clone_flags,
         if ((clone_flags & CLONE_SIGHAND) && !(clone_flags & CLONE_VM))
                 return ERR_PTR(-EINVAL);
 
+        /*
+         * Siblings of global init remain as zombies on exit since they are
+         * not reaped by their parent (swapper). To solve this and to avoid
+         * multi-rooted process trees, prevent global and container-inits
+         * from creating siblings.
+         */
+        if ((clone_flags & CLONE_PARENT) &&
+                                current->signal->flags & SIGNAL_UNKILLABLE)
+                return ERR_PTR(-EINVAL);
+
         retval = security_task_create(clone_flags);
         if (retval)
                 goto fork_out;