Messages in this thread | | | Date | Thu, 11 Oct 2012 20:39:22 +0200 | From | Oleg Nesterov <> | Subject | Re: [PATCH] pidns: limit a size of pid to one page |
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On 10/10, Andrew Vagin wrote: > > A size of pid depends on a level of pidns and now a level of pidns > is not limited, so it can be more than one page. > > Looks reasonable, that it should be limited to a page size. On x86_64 > it will allow to create 125 nested pid namespaces. I don't know a > usecase for which, it will be not enough. When someone finds a > reasonable use case, we can add a config option or a sysctl parameter.
I think this makes sense.
Acked-by: Oleg Nesterov <oleg@redhat.com>
> 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. > > For example my system becomes inaccessible for a few minutes with > 4000 processes. > > Cc: Andrew Morton <akpm@linux-foundation.org> > Cc: Oleg Nesterov <oleg@redhat.com> > Cc: Cyrill Gorcunov <gorcunov@openvz.org> > Cc: "Eric W. Biederman" <ebiederm@xmission.com> > Cc: Pavel Emelyanov <xemul@parallels.com> > Signed-off-by: Andrew Vagin <avagin@openvz.org> > --- > kernel/pid_namespace.c | 6 ++++++ > 1 files changed, 6 insertions(+), 0 deletions(-) > > diff --git a/kernel/pid_namespace.c b/kernel/pid_namespace.c > index b051fa6..bc822e6 100644 > --- a/kernel/pid_namespace.c > +++ b/kernel/pid_namespace.c > @@ -70,12 +70,18 @@ err_alloc: > return NULL; > } > > +/* Limit a size of pid to one page */ > +#define MAX_PID_NS_LEVEL ((PAGE_SIZE - sizeof(struct pid)) / sizeof(struct upid)) > + > 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; > -- > 1.7.1 >
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