[PATCH v2 3/4] tun: keep a kernel copy of the socket filter program

@@ -197,6 +197,7 @@ struct tun_struct {
 	int			sndbuf;
 	struct tap_filter	txflt;
 	struct sock_fprog	fprog;
+	struct sock_fprog_kern	fprog_kern;
 	/* protected by rtnl lock */
 	bool			filter_attached;
 	u32			msg_enable;

@@ -722,6 +723,34 @@ static void tun_force_wake_queue(struct tun_struct *tun,
 	spin_unlock_bh(&tfile->tx_ring.consumer_lock);
 }
 
+/* Copy the filter that @argp points at into the kernel, so that it can be
+ * installed again later, from any context. tun->fprog and tun->fprog_kern
+ * are updated only once the copy succeeded.
+ */
+static int tun_copy_filter(struct tun_struct *tun, struct sock_fprog __user *argp)
+{
+	struct sock_fprog fprog;
+	struct sock_filter *insns;
+
+	if (copy_from_user(&fprog, argp, sizeof(fprog)))
+		return -EFAULT;
+
+	if (!fprog.len || fprog.len > BPF_MAXINSNS)
+		return -EINVAL;
+
+	insns = memdup_array_user(fprog.filter, fprog.len,
+				  sizeof(struct sock_filter));
+	if (IS_ERR(insns))
+		return PTR_ERR(insns);
+
+	kfree(tun->fprog_kern.filter);
+	tun->fprog_kern.len = fprog.len;
+	tun->fprog_kern.filter = insns;
+	tun->fprog = fprog;
+
+	return 0;
+}
+
 static int tun_attach(struct tun_struct *tun, struct file *file,
 		      bool skip_filter, bool napi, bool napi_frags,
 		      bool publish_tun)

@@ -753,7 +782,7 @@ static int tun_attach(struct tun_struct *tun, struct file *file,
 	/* Re-attach the filter to persist device */
 	if (!skip_filter && (tun->filter_attached == true)) {
 		lock_sock(tfile->socket.sk);
-		err = sk_attach_filter(&tun->fprog, tfile->socket.sk);
+		err = sk_attach_filter_kern(&tun->fprog_kern, tfile->socket.sk);
 		release_sock(tfile->socket.sk);
 		if (err)
 			goto out;

@@ -2404,6 +2433,7 @@ static void tun_free_netdev(struct net_device *dev)
 	security_tun_dev_free_security(tun->security);
 	__tun_set_ebpf(tun, &tun->steering_prog, NULL);
 	__tun_set_ebpf(tun, &tun->filter_prog, NULL);
+	kfree(tun->fprog_kern.filter);
 }
 
 static void tun_setup(struct net_device *dev)

@@ -3066,6 +3096,9 @@ static void tun_detach_filter(struct tun_struct *tun, int n)
 		release_sock(tfile->socket.sk);
 	}
 
+	kfree(tun->fprog_kern.filter);
+	tun->fprog_kern.filter = NULL;
+	tun->fprog_kern.len = 0;
 	tun->filter_attached = false;
 }
 

@@ -3077,7 +3110,7 @@ static int tun_attach_filter(struct tun_struct *tun)
 	for (i = 0; i < tun->numqueues; i++) {
 		tfile = rtnl_dereference(tun->tfiles[i]);
 		lock_sock(tfile->socket.sk);
-		ret = sk_attach_filter(&tun->fprog, tfile->socket.sk);
+		ret = sk_attach_filter_kern(&tun->fprog_kern, tfile->socket.sk);
 		release_sock(tfile->socket.sk);
 		if (ret) {
 			tun_detach_filter(tun, i);

@@ -3425,8 +3458,8 @@ static long __tun_chr_ioctl(struct file *file, unsigned int cmd,
 		ret = -EINVAL;
 		if ((tun->flags & TUN_TYPE_MASK) != IFF_TAP)
 			break;
-		ret = -EFAULT;
-		if (copy_from_user(&tun->fprog, argp, sizeof(tun->fprog)))
+		ret = tun_copy_filter(tun, argp);
+		if (ret)
 			break;
 
 		ret = tun_attach_filter(tun);