Subject: Re: Multicast filtering for tun.c [PATCH]

From: Shaun Jackman <[email-masked]>
Date: Wed, 1 Dec 2004 14:03:17 -0800

This patch adds multicast filtering to the TUN network driver, for
packets being sent from the network device to the character device. It
applies against the 2.6.8.1 kernel tree.

Cheers,
Shaun

On Sat, 27 Nov 2004 01:10:06 -0800, Andrew Morton <[email-masked]> wrote:
> Shaun Jackman <[email-masked]> wrote:
> >
> > This patch adds multicast filtering to the TUN network driver,
> 
> You should cc [email-masked] on networking stuff.
> 
> You may not get any feedback on this work.  Persist.  If you get nowhere,
> ping me and I'll help push things along.
> 
> >  This is my first attempt at sending a patch using gmail.
> 
> Send the patch to yourself first, check that the result applies OK.

2004-11-25  Shaun Jackman  <[email-masked]>

	* drivers/net/tun.c: Add multicast filtering for packets
	travelling from the network device to the character device.

	* include/linux/if_tun.h (tun_struct): Add interface flags,
	a hardware device addres, and a multicast filter.

diff -ur linux-2.6.8.1.orig/drivers/net/tun.c linux-2.6.8.1/drivers/net/tun.c
--- linux-2.6.8.1.orig/drivers/net/tun.c	2004-08-14 03:55:23.000000000 -0700
+++ linux-2.6.8.1/drivers/net/tun.c	2004-11-25 17:00:22.000000000 -0800
@@ -41,6 +41,7 @@
 #include <linux/if_arp.h>
 #include <linux/if_ether.h>
 #include <linux/if_tun.h>
+#include <linux/crc32.h>
 
 #include <asm/system.h>
 #include <asm/uaccess.h>
@@ -104,11 +105,42 @@
 	return 0;
 }
 
-static void tun_net_mclist(struct net_device *dev)
+/** Add the specified Ethernet address to this multicast filter. */
+static void
+add_multi(u32* filter, const u8* addr)
 {
-	/* Nothing to do for multicast filters. 
-	 * We always accept all frames. */
-	return;
+	int bit_nr = ether_crc(ETH_ALEN, addr) >> 26;
+	filter[bit_nr >> 5] |= 1 << (bit_nr & 31);
+}
+
+/** Remove the specified Ethernet addres from this multicast filter. */
+static void
+del_multi(u32* filter, const u8* addr)
+{
+	int bit_nr = ether_crc(ETH_ALEN, addr) >> 26;
+	filter[bit_nr >> 5] &= ~(1 << (bit_nr & 31));
+}
+
+/** Update the list of multicast groups to which the network device belongs.
+ * This list is used to filter packets being sent from the character device to
+ * the network device. */
+static void
+tun_net_mclist(struct net_device *dev)
+{
+	struct tun_struct *tun = netdev_priv(dev);
+	const struct dev_mc_list *mclist;
+	int i;
+	DBG(KERN_DEBUG "%s: tun_net_mclist: mc_count %d\n",
+			dev->name, dev->mc_count);
+	memset(tun->chr_filter, 0, sizeof tun->chr_filter);
+	for (i = 0, mclist = dev->mc_list; i < dev->mc_count && mclist != NULL;
+			i++, mclist = mclist->next) {
+		add_multi(tun->net_filter, mclist->dmi_addr);
+		DBG(KERN_DEBUG "%s: tun_net_mclist: %x:%x:%x:%x:%x:%x\n",
+				dev->name,
+				mclist->dmi_addr[0], mclist->dmi_addr[1], mclist->dmi_addr[2],
+				mclist->dmi_addr[3], mclist->dmi_addr[4], mclist->dmi_addr[5]);
+	}
 }
 
 static struct net_device_stats *tun_net_stats(struct net_device *dev)
@@ -301,6 +333,10 @@
 
 	add_wait_queue(&tun->read_wait, &wait);
 	while (len) {
+		const u8 ones[ ETH_ALEN] = { 0xff, 0xff, 0xff, 0xff, 0xff, 0xff };
+		u8 addr[ ETH_ALEN];
+		int bit_nr;
+
 		current->state = TASK_INTERRUPTIBLE;
 
 		/* Read frames from the queue */
@@ -320,10 +356,37 @@
 		}
 		netif_start_queue(tun->dev);
 
-		ret = tun_put_user(tun, skb, (struct iovec *) iv, len);
-
-		kfree_skb(skb);
-		break;
+		/** Decide whether to accept this packet. This code is designed to
+		 * behave identically to an Ethernet interface. Accept the packet if
+		 * - we are promiscuous.
+		 * - the packet is addressed to us.
+		 * - the packet is broadcast.
+		 * - the packet is multicast and
+		 *   - we are multicast promiscous.
+		 *   - we belong to the multicast group.
+		 */
+		memcpy(addr, skb->data, min(sizeof addr, skb->len));
+		bit_nr = ether_crc(sizeof addr, addr) >> 26;
+		if ((tun->if_flags & IFF_PROMISC) ||
+				memcmp(addr, tun->dev_addr, sizeof addr) == 0 ||
+				memcmp(addr, ones, sizeof addr) == 0 ||
+				(((addr[0] == 1 && addr[1] == 0 && addr[2] == 0x5e) ||
+				  (addr[0] == 0x33 && addr[1] == 0x33)) &&
+				 ((tun->if_flags & IFF_ALLMULTI) ||
+				  (tun->chr_filter[bit_nr >> 5] & (1 << (bit_nr & 31)))))) {
+			DBG(KERN_DEBUG "%s: tun_chr_readv: accepted: %x:%x:%x:%x:%x:%x\n",
+					tun->dev->name, addr[0], addr[1], addr[2],
+					addr[3], addr[4], addr[5]);
+			ret = tun_put_user(tun, skb, (struct iovec *) iv, len);
+			kfree_skb(skb);
+			break;
+		} else {
+			DBG(KERN_DEBUG "%s: tun_chr_readv: rejected: %x:%x:%x:%x:%x:%x\n",
+					tun->dev->name, addr[0], addr[1], addr[2],
+					addr[3], addr[4], addr[5]);
+			kfree_skb(skb);
+			continue;
+		}
 	}
 
 	current->state = TASK_RUNNING;
@@ -417,6 +480,12 @@
 		tun = netdev_priv(dev);
 		tun->dev = dev;
 		tun->flags = flags;
+		/* Be promiscuous by default to maintain previous behaviour. */
+		tun->if_flags = IFF_PROMISC;
+		/* Generate random Ethernet address. */
+		*(u16 *)tun->dev_addr = htons(0x00FF);
+		get_random_bytes(tun->dev_addr + sizeof(u16), 4);
+		memset(tun->chr_filter, 0, sizeof tun->chr_filter);
 
 		tun_net_init(dev);
 
@@ -457,13 +526,16 @@
 			 unsigned int cmd, unsigned long arg)
 {
 	struct tun_struct *tun = file->private_data;
+	void __user* argp = (void __user*)arg;
+	struct ifreq ifr;
+
+	if (cmd == TUNSETIFF || _IOC_TYPE(cmd) == 0x89)
+		if (copy_from_user(&ifr, argp, sizeof ifr))
+			return -EFAULT;
 
 	if (cmd == TUNSETIFF && !tun) {
-		struct ifreq ifr;
 		int err;
 
-		if (copy_from_user(&ifr, (void __user *)arg, sizeof(ifr)))
-			return -EFAULT;
 		ifr.ifr_name[IFNAMSIZ-1] = '\0';
 
 		rtnl_lock();
@@ -473,7 +545,7 @@
 		if (err)
 			return err;
 
-		if (copy_to_user((void __user *)arg, &ifr, sizeof(ifr)))
+		if (copy_to_user(argp, &ifr, sizeof(ifr)))
 			return -EFAULT;
 		return 0;
 	}
@@ -519,6 +591,61 @@
 		break;
 #endif
 
+	case SIOCGIFFLAGS:
+		ifr.ifr_flags = tun->if_flags;
+		if (copy_to_user( argp, &ifr, sizeof ifr))
+			return -EFAULT;
+		return 0;
+	
+	case SIOCSIFFLAGS:
+		/** Set the character device's interface flags. Currently only
+		 * IFF_PROMISC and IFF_ALLMULTI are used. */
+		tun->if_flags = ifr.ifr_flags;
+		DBG(KERN_INFO "%s: interface flags 0x%lx\n",
+				tun->dev->name, tun->if_flags);
+		return 0;
+	
+	case SIOCGIFHWADDR:
+		memcpy(ifr.ifr_hwaddr.sa_data, tun->dev_addr,
+				min(sizeof ifr.ifr_hwaddr.sa_data, sizeof tun->dev_addr));
+		if (copy_to_user( argp, &ifr, sizeof ifr))
+			return -EFAULT;
+		return 0;
+	
+	case SIOCSIFHWADDR:
+		/** Set the character device's hardware address. This is used when
+		 * filtering packets being sent from the network device to the character
+		 * device. */
+		memcpy(tun->dev_addr, ifr.ifr_hwaddr.sa_data,
+				min(sizeof ifr.ifr_hwaddr.sa_data, sizeof tun->dev_addr));
+		DBG(KERN_DEBUG "%s: set hardware address: %x:%x:%x:%x:%x:%x\n",
+				tun->dev->name,
+				tun->dev_addr[0], tun->dev_addr[1], tun->dev_addr[2],
+				tun->dev_addr[3], tun->dev_addr[4], tun->dev_addr[5]);
+		return 0;
+	
+	case SIOCADDMULTI:
+		/** Add the specified group to the character device's multicast filter
+		 * list. */
+		add_multi(tun->chr_filter, ifr.ifr_hwaddr.sa_data);
+		DBG(KERN_DEBUG "%s: add multi: %x:%x:%x:%x:%x:%x\n",
+				tun->dev->name,
+				(u8)ifr.ifr_hwaddr.sa_data[0], (u8)ifr.ifr_hwaddr.sa_data[1],
+				(u8)ifr.ifr_hwaddr.sa_data[2], (u8)ifr.ifr_hwaddr.sa_data[3],
+				(u8)ifr.ifr_hwaddr.sa_data[4], (u8)ifr.ifr_hwaddr.sa_data[5]);
+		return 0;
+	
+	case SIOCDELMULTI:
+		/** Remove the specified group from the character device's multicast
+		 * filter list. */
+		del_multi(tun->chr_filter, ifr.ifr_hwaddr.sa_data);
+		DBG(KERN_DEBUG "%s: del multi: %x:%x:%x:%x:%x:%x\n",
+				tun->dev->name,
+				(u8)ifr.ifr_hwaddr.sa_data[0], (u8)ifr.ifr_hwaddr.sa_data[1],
+				(u8)ifr.ifr_hwaddr.sa_data[2], (u8)ifr.ifr_hwaddr.sa_data[3],
+				(u8)ifr.ifr_hwaddr.sa_data[4], (u8)ifr.ifr_hwaddr.sa_data[5]);
+		return 0;
+
 	default:
 		return -EINVAL;
 	};
diff -ur linux-2.6.8.1.orig/include/linux/if_tun.h
linux-2.6.8.1/include/linux/if_tun.h
--- linux-2.6.8.1.orig/include/linux/if_tun.h	2004-08-14
03:55:09.000000000 -0700
+++ linux-2.6.8.1/include/linux/if_tun.h	2004-11-25 16:47:31.000000000 -0800
@@ -45,6 +45,11 @@
 
 	struct fasync_struct    *fasync;
 
+	unsigned long if_flags;
+	u8 dev_addr[ETH_ALEN];
+	u32 chr_filter[2];
+	u32 net_filter[2];
+
 #ifdef TUN_DEBUG	
 	int debug;
 #endif