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>

diff --git a/kernel/fork.c b/kernel/fork.c
index 51ad0b0..b51fd2c 100644 (file)
--- 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;