pidns: Outlaw thread creation after unshare(CLONE_NEWPID)
The sequence:
unshare(CLONE_NEWPID)
clone(CLONE_THREAD|CLONE_SIGHAND|CLONE_VM)
Creates a new process in the new pid namespace without setting
pid_ns->child_reaper. After forking this results in a NULL
pointer dereference.
Avoid this and other nonsense scenarios that can show up after
creating a new pid namespace with unshare by adding a new
check in copy_prodcess.
Pointed-out-by: Oleg Nesterov <oleg@redhat.com>
Acked-by: Oleg Nesterov <oleg@redhat.com>
Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>
diff --git a/kernel/fork.c b/kernel/fork.c
index a31b823..65ca6d2 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -1166,6 +1166,14 @@
current->signal->flags & SIGNAL_UNKILLABLE)
return ERR_PTR(-EINVAL);
+ /*
+ * If the new process will be in a different pid namespace
+ * don't allow the creation of threads.
+ */
+ if ((clone_flags & (CLONE_VM|CLONE_NEWPID)) &&
+ (task_active_pid_ns(current) != current->nsproxy->pid_ns))
+ return ERR_PTR(-EINVAL);
+
retval = security_task_create(clone_flags);
if (retval)
goto fork_out;