Messages in this thread | | | Date | Sat, 20 Oct 2012 17:21:00 +0200 | From | Oleg Nesterov <> | Subject | Re: [PATCH] pidns: limit the nesting depth of pid namespaces |
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On 10/12, 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. > > 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>
Acked-by: Oleg Nesterov <oleg@redhat.com>
> --- > 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..598bfb3 100644 > --- 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; > -- > 1.7.1 >
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