Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755654Ab2JFT4h (ORCPT ); Sat, 6 Oct 2012 15:56:37 -0400 Received: from mailhub.sw.ru ([195.214.232.25]:25178 "EHLO relay.sw.ru" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753396Ab2JFT4f (ORCPT ); Sat, 6 Oct 2012 15:56:35 -0400 From: Andrew Vagin To: linux-kernel@vger.kernel.org Cc: criu@openvz.org, Pavel Emelyanov , Cyrill Gorcunov , Andrew Vagin , Andrew Morton , "Eric W. Biederman" Subject: [PATCH] pidns: remove recursion from free_pid_ns (v3) Date: Sat, 6 Oct 2012 23:56:33 +0400 Message-Id: <1349553393-902065-1-git-send-email-avagin@openvz.org> X-Mailer: git-send-email 1.7.1 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2424 Lines: 86 Here is a stack trace of recursion: free_pid_ns(parent) put_pid_ns(parent) kref_put(&ns->kref, free_pid_ns); free_pid_ns This patch turns recursion into loops. pidns can be nested many times, so in case of recursion a simple user space program can provoke a kernel panic due to exceed of a kernel stack. v2: * don't check parent on NULL * use atomic_dec_and_test(&kref->refcount) v3: Fix coding style issue Acked-by: Cyrill Gorcunov Reviewed-by: Oleg Nesterov Cc: Andrew Morton Cc: "Eric W. Biederman" Cc: Pavel Emelyanov Signed-off-by: Andrew Vagin --- include/linux/kref.h | 12 ++++++++++++ kernel/pid_namespace.c | 16 ++++++++++++---- 2 files changed, 24 insertions(+), 4 deletions(-) diff --git a/include/linux/kref.h b/include/linux/kref.h index 65af688..2844262 100644 --- a/include/linux/kref.h +++ b/include/linux/kref.h @@ -95,6 +95,18 @@ static inline int kref_put(struct kref *kref, void (*release)(struct kref *kref) return kref_sub(kref, 1, release); } +/** + * kref_put - decrement refcount for object. + * @kref: object. + * + * Decrement the refcount. + * Return 1 if refcount is zero. + */ +static inline int __kref_put(struct kref *kref) +{ + return atomic_dec_and_test(&kref->refcount); +} + static inline int kref_put_mutex(struct kref *kref, void (*release)(struct kref *kref), struct mutex *lock) diff --git a/kernel/pid_namespace.c b/kernel/pid_namespace.c index 6144bab..b051fa6 100644 --- a/kernel/pid_namespace.c +++ b/kernel/pid_namespace.c @@ -138,11 +138,19 @@ void free_pid_ns(struct kref *kref) ns = container_of(kref, struct pid_namespace, kref); - parent = ns->parent; - destroy_pid_namespace(ns); + while (1) { + parent = ns->parent; + destroy_pid_namespace(ns); - if (parent != NULL) - put_pid_ns(parent); + if (parent == &init_pid_ns) + break; + + /* kref_put cannot be used for avoiding recursion */ + if (__kref_put(&parent->kref) == 0) + break; + + ns = parent; + } } void zap_pid_ns_processes(struct pid_namespace *pid_ns) -- 1.7.1 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/