netdev - Re: [PATCH bpf-next v2 1/2] bpf: support BPF_PROG_QUERY for BPF_FLOW_DISSECTOR attach

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Message-ID: <20190424210639.GD1247@mini-arch>
Date:   Wed, 24 Apr 2019 14:06:39 -0700
From:   Stanislav Fomichev <sdf@...ichev.me>
To:     Jann Horn <jannh@...gle.com>
Cc:     Stanislav Fomichev <sdf@...gle.com>,
        Network Development <netdev@...r.kernel.org>,
        bpf@...r.kernel.org, "David S. Miller" <davem@...emloft.net>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        jakub.kicinski@...ronome.com, quentin.monnet@...ronome.com
Subject: Re: [PATCH bpf-next v2 1/2] bpf: support BPF_PROG_QUERY for
 BPF_FLOW_DISSECTOR attach_type

On 04/24, Jann Horn wrote:
> On Wed, Apr 24, 2019 at 6:09 PM Stanislav Fomichev <sdf@...gle.com> wrote:
> > target_fd is target namespace. If there is a flow dissector BPF program
> > attached to that namespace, its (single) id is returned.
> >
> > v2:
> > * don't sleep in rcu critical section (Jakub Kicinski)
> > * check input prog_cnt (exit early)
> >
> > Signed-off-by: Stanislav Fomichev <sdf@...gle.com>
> [...]
> > +int skb_flow_dissector_prog_query(const union bpf_attr *attr,
> > +                                 union bpf_attr __user *uattr)
> > +{
> [...]
> > +       net = get_net_ns_by_fd(attr->query.target_fd);
> > +       if (IS_ERR(net))
> > +               return PTR_ERR(net);
> 
> At this point, you're holding a refcounted reference to `net`. It
> looks like that reference is never dropped?
Ah, indeed, put_net is missing, thanks!

> > +
> > +       rcu_read_lock();
> > +       attached = rcu_dereference(net->flow_dissector_prog);
> > +       if (attached) {
> > +               prog_cnt = 1;
> > +               prog_id = attached->aux->id;
> > +       }
> > +       rcu_read_unlock();
> > +
> > +       if (copy_to_user(&uattr->query.attach_flags, &flags, sizeof(flags)))
> > +               return -EFAULT;
> [...]
> > +}