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    SubjectRe: [PATCH 3/7] ns proc: Add support for the network namespace.
    Date
    Nathan Lynch <ntl@pobox.com> writes:

    > On Fri, 2011-05-06 at 19:24 -0700, Eric W. Biederman wrote:
    >> diff --git a/net/core/net_namespace.c b/net/core/net_namespace.c
    >> index 3f86026..bf7707e 100644
    >> --- a/net/core/net_namespace.c
    >> +++ b/net/core/net_namespace.c
    >> @@ -573,3 +573,34 @@ void unregister_pernet_device(struct pernet_operations *ops)
    >> mutex_unlock(&net_mutex);
    >> }
    >> EXPORT_SYMBOL_GPL(unregister_pernet_device);
    >> +
    >> +#ifdef CONFIG_NET_NS
    >> +static void *netns_get(struct task_struct *task)
    >> +{
    >> + struct net *net;
    >> + rcu_read_lock();
    >> + net = get_net(task->nsproxy->net_ns);
    >
    > This should use task_nsproxy() and check the result before grabbing the
    > net_ns, but I think you fix that in a later patch.
    >
    > Regardless, it looks as if all the proc_ns_ops->get() implementations
    > really just want the nsproxy, so maybe the get() methods should take
    > that instead of the task_struct, and proc_ns_instantiate() should do
    > something like:
    >
    > struct nsproxy *nsproxy;
    > ...
    >
    > ei->ns_ops = ns_ops;
    > error = -ESRCH;
    > rcu_read_lock();
    > nsproxy = task_nsproxy(task);
    > rcu_read_unlock();
    > if (!nsproxy)
    > got out;
    > ei->ns = ns_ops->get(nsproxy);
    >
    >
    > So then the zombie check is consolidated in one place instead of having
    > to do it in every get() method.

    For the pid namespace at least I want the task not the nsproxy,
    so I can use task_active_pid_namespace().

    I admit that is a little asymmetrical with the install, but at
    least until the details of getting the pid namespace working in
    this context are worked out I don't want to reconsider the
    current design.

    There is also the user namespace that does not even exist in
    nsproxy to consider. I will worry about that namespace when
    it happens.

    Ultimately nsproxy is an space/time optimization that not all
    namespaces use so forcing it in the design is probably not
    what we want.

    >> + rcu_read_unlock();
    >> + return net;
    >> +}
    >> +
    >> +static void netns_put(void *ns)
    >> +{
    >> + put_net(ns);
    >> +}
    >> +
    >> +static int netns_install(struct nsproxy *nsproxy, void *ns)
    >> +{
    >> + put_net(nsproxy->net_ns);
    >> + nsproxy->net_ns = get_net(ns);
    >> + return 0;
    >> +}
    >
    > This introduces a window where, potentially, nsproxy->net_ns is stale
    > before it is updated with the namespace which is being attached, no?
    > (Same concern applies to other install methods in the patch set). It
    > seems possible to oops the kernel in this window by looking up
    > /proc/$PID/ns/net while $PID is in the midst of setns().

    Except the nsproxy being referred to is a brand new nsproxy, with an
    extra reference count on every namespace. current->nsproxy still
    contains the reference counts of the current process.

    Eric



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