From b7e0bb551032cefaa08f34930409fe1bd6cffcd7 Mon Sep 17 00:00:00 2001 From: Cyrill Gorcunov Date: Fri, 12 Oct 2012 15:22:44 +1100 Subject: [PATCH] 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. Signed-off-by: Cyrill Gorcunov Cc: Andrew Vagin Cc: Oleg Nesterov Cc: "Eric W. Biederman" Cc: Pavel Emelyanov Cc: Greg KH Signed-off-by: Andrew Morton --- include/linux/pid_namespace.h | 8 +------- kernel/pid_namespace.c | 19 +++++++++++++------ 2 files changed, 14 insertions(+), 13 deletions(-) diff --git a/include/linux/pid_namespace.h b/include/linux/pid_namespace.h index 00474b047145..65e3e87eacc5 100644 --- a/include/linux/pid_namespace.h +++ b/include/linux/pid_namespace.h @@ -47,15 +47,9 @@ static inline struct pid_namespace *get_pid_ns(struct pid_namespace *ns) } extern struct pid_namespace *copy_pid_ns(unsigned long flags, struct pid_namespace *ns); -extern void free_pid_ns(struct kref *kref); extern void zap_pid_ns_processes(struct pid_namespace *pid_ns); extern int reboot_pid_ns(struct pid_namespace *pid_ns, int cmd); - -static inline void put_pid_ns(struct pid_namespace *ns) -{ - if (ns != &init_pid_ns) - kref_put(&ns->kref, free_pid_ns); -} +extern void put_pid_ns(struct pid_namespace *ns); #else /* !CONFIG_PID_NS */ #include diff --git a/kernel/pid_namespace.c b/kernel/pid_namespace.c index 478bad2745e3..14f450488c5e 100644 --- a/kernel/pid_namespace.c +++ b/kernel/pid_namespace.c @@ -133,17 +133,24 @@ struct pid_namespace *copy_pid_ns(unsigned long flags, struct pid_namespace *old 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); +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(free_pid_ns); -- 2.39.5