From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S934203Ab2JWX5B (ORCPT ); Tue, 23 Oct 2012 19:57:01 -0400 Received: from mail.linuxfoundation.org ([140.211.169.12]:57810 "EHLO mail.linuxfoundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S933579Ab2JWX45 (ORCPT ); Tue, 23 Oct 2012 19:56:57 -0400 Date: Tue, 23 Oct 2012 16:56:51 -0700 From: Andrew Morton To: Andrew Vagin Cc: linux-kernel@vger.kernel.org, Oleg Nesterov , Cyrill Gorcunov , "Eric W. Biederman" , Pavel Emelyanov Subject: Re: [PATCH] pidns: limit the nesting depth of pid namespaces Message-Id: <20121023165651.88af399d.akpm@linux-foundation.org> In-Reply-To: <1350045042-1369134-1-git-send-email-avagin@openvz.org> References: <1350045042-1369134-1-git-send-email-avagin@openvz.org> X-Mailer: Sylpheed 3.0.2 (GTK+ 2.20.1; x86_64-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, 12 Oct 2012 16:30:42 +0400 Andrew Vagin wrote: > 'struct pid' is a "variable sized struct" - a header with an array > of upids at the end. > > A size of the array depends on a level (depth) of pid namespaces. Now > a level of pidns is not limited, so 'struct pid' can be more than one > page. > > Looks reasonable, that it should be less than a page. MAX_PIS_NS_LEVEL > is not calculated from PAGE_SIZE, because in this case it depends on > architectures, config options and it will be reduced, if someone adds a > new fields in struct pid or struct upid. > > I suggest to set MAX_PIS_NS_LEVEL = 32, because it saves ability to > expand "struct pid" and it's more than enough for all known for me > use-cases. When someone finds a reasonable use case, we can add a > config option or a sysctl parameter. > > In addition it will reduce effect of another problem, when we have many > nested namespaces and the oldest one starts dying. zap_pid_ns_processe > will be called for each namespace and find_vpid will be called for each > process in a namespace. find_vpid will be called minimum max_level^2 / 2 > times. The reason of that is that when we found a bit in pidmap, we > can't determine this pidns is top for this process or it isn't. > > vpid is a heavy operation, so a fork bomb, which create many nested > namespace, can do a system inaccessible for a long time. > > --- a/kernel/pid_namespace.c > +++ b/kernel/pid_namespace.c > @@ -70,12 +70,18 @@ err_alloc: > return NULL; > } > > +/* MAX_PID_NS_LEVEL is needed for limiting size of 'struct pid' */ > +#define MAX_PID_NS_LEVEL 32 > + > static struct pid_namespace *create_pid_namespace(struct pid_namespace *parent_pid_ns) > { > struct pid_namespace *ns; > unsigned int level = parent_pid_ns->level + 1; > int i, err = -ENOMEM; > > + if (level > MAX_PID_NS_LEVEL) > + goto out; > + > ns = kmem_cache_zalloc(pid_ns_cachep, GFP_KERNEL); > if (ns == NULL) > goto out; hm, OK. This will kind-of fix the free_pid_ns()-excessive-recursion issue which we already fixed by other means ;) I don't think this problem is serious enough to bother backporting into -stable but I guess we can/should do it in 3.7. Agree? I think that returning -ENOMEM in response to an excessive nesting attempt is misleading - the system *didn't* run out of memory. EINVAL is better? From: Andrew Morton Subject: pidns-limit-the-nesting-depth-of-pid-namespaces-fix return -EINVAL in response to excessive nesting, not -ENOMEM Cc: "Eric W. Biederman" Cc: Andrew Vagin Cc: Cyrill Gorcunov Cc: Oleg Nesterov Cc: Pavel Emelyanov Signed-off-by: Andrew Morton --- kernel/pid_namespace.c | 8 ++++++-- 1 file changed, 6 insertions(+), 2 deletions(-) diff -puN kernel/pid_namespace.c~pidns-limit-the-nesting-depth-of-pid-namespaces-fix kernel/pid_namespace.c --- a/kernel/pid_namespace.c~pidns-limit-the-nesting-depth-of-pid-namespaces-fix +++ a/kernel/pid_namespace.c @@ -78,11 +78,15 @@ static struct pid_namespace *create_pid_ { struct pid_namespace *ns; unsigned int level = parent_pid_ns->level + 1; - int i, err = -ENOMEM; + int i; + int err; - if (level > MAX_PID_NS_LEVEL) + if (level > MAX_PID_NS_LEVEL) { + err = -EINVAL; goto out; + } + err = -ENOMEM; ns = kmem_cache_zalloc(pid_ns_cachep, GFP_KERNEL); if (ns == NULL) goto out; _