Re:Re: [PATCH] net/packet: fix race condition between fanout_add and __unregister_prot_hook

On Fri, Sep 15, 2017 at 10:46 AM, Willem de Bruijn
[off-list ref] wrote:

In case of failure we also need to unlink and free match. I
sent the following:

http://patchwork.ozlabs.org/patch/813945/

+       spin_lock(&po->bind_lock);
+       if (po->running &&
+           match->type == type &&
           match->prot_hook.type == po->prot_hook.type &&
           match->prot_hook.dev == po->prot_hook.dev) {
                err = -ENOSPC;

@@ -1761,6 +1760,13 @@  static int fanout_add(struct sock *sk, u16 id, u16 type_flags)
                          err = 0;
                }
       }
+       spin_unlock(&po->bind_lock);
+
+       if (err && !refcount_read(&match->sk_ref)) {
+                list_del(&match->list);
+                kfree(match);
+       }

In the function fanout_add add spin_lock to protect po-> running and po-> fanout, 
then whether it should be in the function fanout_release also add spin_lock protection ?

static struct packet_fanout *fanout_release(struct sock *sk)
....
        mutex_lock(&fanout_mutex);
        f = po->fanout;
        if (f) {
                po->fanout = NULL;