pidns: remove recursion from free_pid_ns()
free_pid_ns() operates in a recursive fashion:
free_pid_ns(parent)
put_pid_ns(parent)
kref_put(&ns->kref, free_pid_ns);
free_pid_ns
thus if there was a huge nesting of namespaces the userspace may trigger
avalanche calling of free_pid_ns leading to kernel stack exhausting and a
panic eventually.
This patch turns the recursion into an iterative loop.
Based on a patch by Andrew Vagin.
[akpm@linux-foundation.org: export put_pid_ns() to modules]
Signed-off-by: Cyrill Gorcunov <gorcunov@openvz.org>
Cc: Andrew Vagin <avagin@openvz.org>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: "Eric W. Biederman" <ebiederm@xmission.com>
Cc: Pavel Emelyanov <xemul@parallels.com>
Cc: Greg KH <greg@kroah.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/kernel/pid_namespace.c b/kernel/pid_namespace.c
index 478bad2..eb00be2 100644
--- a/kernel/pid_namespace.c
+++ b/kernel/pid_namespace.c
@@ -133,19 +133,26 @@
return create_pid_namespace(old_ns);
}
-void free_pid_ns(struct kref *kref)
+static void free_pid_ns(struct kref *kref)
{
- struct pid_namespace *ns, *parent;
+ struct pid_namespace *ns;
ns = container_of(kref, struct pid_namespace, kref);
-
- parent = ns->parent;
destroy_pid_namespace(ns);
-
- if (parent != NULL)
- put_pid_ns(parent);
}
-EXPORT_SYMBOL_GPL(free_pid_ns);
+
+void put_pid_ns(struct pid_namespace *ns)
+{
+ struct pid_namespace *parent;
+
+ while (ns != &init_pid_ns) {
+ parent = ns->parent;
+ if (!kref_put(&ns->kref, free_pid_ns))
+ break;
+ ns = parent;
+ }
+}
+EXPORT_SYMBOL_GPL(put_pid_ns);
void zap_pid_ns_processes(struct pid_namespace *pid_ns)
{