filter: Allow to create sk-unattached filters

Today, BPF filters are bind to sockets. Since BPF machine becomes handy
for other purposes, this patch allows to create unattached filter.
Signed-off-by: Jiri Pirko <jpirko@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/linux/filter.h

@@ -153,6 +153,9 @@ static inline unsigned int sk_filter_len(const struct sk_filter *fp)
 extern int sk_filter(struct sock *sk, struct sk_buff *skb);
 extern unsigned int sk_run_filter(const struct sk_buff *skb,
 				  const struct sock_filter *filter);
+extern int sk_unattached_filter_create(struct sk_filter **pfp,
+				       struct sock_fprog *fprog);
+extern void sk_unattached_filter_destroy(struct sk_filter *fp);
 extern int sk_attach_filter(struct sock_fprog *fprog, struct sock *sk);
 extern int sk_detach_filter(struct sock *sk);
 extern int sk_chk_filter(struct sock_filter *filter, unsigned int flen);

net/core/filter.c

@@ -587,6 +587,67 @@ void sk_filter_release_rcu(struct rcu_head *rcu)
 }
 EXPORT_SYMBOL(sk_filter_release_rcu);
 
+static int __sk_prepare_filter(struct sk_filter *fp)
+{
+	int err;
+
+	fp->bpf_func = sk_run_filter;
+
+	err = sk_chk_filter(fp->insns, fp->len);
+	if (err)
+		return err;
+
+	bpf_jit_compile(fp);
+	return 0;
+}
+
+/**
+ *	sk_unattached_filter_create - create an unattached filter
+ *	@fprog: the filter program
+ *	@sk: the socket to use
+ *
+ * Create a filter independent ofr any socket. We first run some
+ * sanity checks on it to make sure it does not explode on us later.
+ * If an error occurs or there is insufficient memory for the filter
+ * a negative errno code is returned. On success the return is zero.
+ */
+int sk_unattached_filter_create(struct sk_filter **pfp,
+				struct sock_fprog *fprog)
+{
+	struct sk_filter *fp;
+	unsigned int fsize = sizeof(struct sock_filter) * fprog->len;
+	int err;
+
+	/* Make sure new filter is there and in the right amounts. */
+	if (fprog->filter == NULL)
+		return -EINVAL;
+
+	fp = kmalloc(fsize + sizeof(*fp), GFP_KERNEL);
+	if (!fp)
+		return -ENOMEM;
+	memcpy(fp->insns, fprog->filter, fsize);
+
+	atomic_set(&fp->refcnt, 1);
+	fp->len = fprog->len;
+
+	err = __sk_prepare_filter(fp);
+	if (err)
+		goto free_mem;
+
+	*pfp = fp;
+	return 0;
+free_mem:
+	kfree(fp);
+	return err;
+}
+EXPORT_SYMBOL_GPL(sk_unattached_filter_create);
+
+void sk_unattached_filter_destroy(struct sk_filter *fp)
+{
+	sk_filter_release(fp);
+}
+EXPORT_SYMBOL_GPL(sk_unattached_filter_destroy);
+
 /**
  *	sk_attach_filter - attach a socket filter
  *	@fprog: the filter program
@@ -617,16 +678,13 @@ int sk_attach_filter(struct sock_fprog *fprog, struct sock *sk)
 
 	atomic_set(&fp->refcnt, 1);
 	fp->len = fprog->len;
-	fp->bpf_func = sk_run_filter;
 
-	err = sk_chk_filter(fp->insns, fp->len);
+	err = __sk_prepare_filter(fp);
 	if (err) {
 		sk_filter_uncharge(sk, fp);
 		return err;
 	}
 
-	bpf_jit_compile(fp);
-
 	old_fp = rcu_dereference_protected(sk->sk_filter,
 					   sock_owned_by_user(sk));
 	rcu_assign_pointer(sk->sk_filter, fp);