/* * Handle incoming frames * Linux ethernet bridge * * Authors: * Lennert Buytenhek <buytenh@gnu.org> * * $Id: br_input.c,v 1.10 2001/12/24 04:50:20 davem Exp $ * * This program is free software; you can redistribute it and/or * modify it under the terms of the GNU General Public License * as published by the Free Software Foundation; either version * 2 of the License, or (at your option) any later version. */ #include <linux/kernel.h> #include <linux/netdevice.h> #include <linux/etherdevice.h> #include <linux/netfilter_bridge.h> #include "br_private.h" /* Bridge group multicast address 802.1d (pg 51). */ const u8 br_group_address[ETH_ALEN] = { 0x01, 0x80, 0xc2, 0x00, 0x00, 0x00 }; static void br_pass_frame_up(struct net_bridge *br, struct sk_buff *skb) { struct net_device *indev; br->statistics.rx_packets++; br->statistics.rx_bytes += skb->len; /* * 修改接收设备为网桥接口 * 这样在下面的NF_BR_LOCAL_IN hook后调用netif_receive_skb时 * 进入handle_bridge便不再进行网桥的处理了 * * 这样对上一层协议栈来说,它只看到网桥接口 */ indev = skb->dev; skb->dev = br->dev; NF_HOOK(PF_BRIDGE, NF_BR_LOCAL_IN, skb, indev, NULL, netif_receive_skb); } /* note: already called with rcu_read_lock (preempt_disabled) */ int br_handle_frame_finish(struct sk_buff *skb) { const unsigned char *dest = eth_hdr(skb)->h_dest; struct net_bridge_port *p = rcu_dereference(skb->dev->br_port); struct net_bridge *br; struct net_bridge_fdb_entry *dst; struct sk_buff *skb2; if (!p || p->state == BR_STATE_DISABLED) goto drop; /* insert into forwarding database after filtering to avoid spoofing(欺骗) */ /* 使用数据包的源MAC地址来更新CAM表(mac转发表) */ br = p->br; br_fdb_update(br, p, eth_hdr(skb)->h_source); if (p->state == BR_STATE_LEARNING) goto drop; /* The packet skb2 goes to the local host (NULL to skip). */ skb2 = NULL; /* * 混杂模式 * 实际上网桥接口通常都应该是混杂模式的 * * 如果网桥的虚拟网卡处于混杂模式 * 那么每个接收到的数据包都需要克隆一份送到AF_PACKET协议处理 * (网络软中断函数net_rx_action中ptype_all链的处理) */ if (br->dev->flags & IFF_PROMISC) skb2 = skb; dst = NULL; /* 目的MAC为二层广播或多播,则需要向本机的上层协议栈传送这个数据包 * 就不需要为该报文找出口了,要向除接收端口外的其他所有端口发送 */ if (is_multicast_ether_addr(dest)) { br->statistics.multicast++; skb2 = skb; } else if ((dst = __br_fdb_get(br, dest)) && dst->is_local) {/* 根据dest查找出接口port */ skb2 = skb; /* Do not forward the packet since it's local. */ skb = NULL; } if (skb2 == skb)/* promisc, clone the skb to local */ skb2 = skb_clone(skb, GFP_ATOMIC); if (skb2)/* promisc or is_local */ br_pass_frame_up(br, skb2); /* only forward it on the packet is not local 发送端和接收端是同一端口,则不转发 */ if (skb) { if (dst)/* 由于dst已经找到,现在知道要走br_forward了 */ br_forward(dst->dst, skb);/* 单播转发 */ else /* CAM表中没有,只能flood了 或者该帧是多播包或二层广播包 */ br_flood_forward(br, skb);/* 广播转发 */ } out: return 0; drop: kfree_skb(skb); goto out;/* ... */ } /* note: already called with rcu_read_lock (preempt_disabled) */ static int br_handle_local_finish(struct sk_buff *skb) { struct net_bridge_port *p = rcu_dereference(skb->dev->br_port); if (p) br_fdb_update(p->br, p, eth_hdr(skb)->h_source); return 0; /* process further */ } /* Does address match the link local multicast address. * 01:80:c2:00:00:0X */ static inline int is_link_local(const unsigned char *dest) { __be16 *a = (__be16 *)dest; static const __be16 *b = (const __be16 *)br_group_address; static const __be16 m = __constant_cpu_to_be16(0xfff0); return ((a[0] ^ b[0]) | (a[1] ^ b[1]) | ((a[2] ^ b[2]) & m)) == 0; } /* 网桥的处理函数 * Called via br_handle_frame_hook. * Return NULL if skb is handled * note: already called with rcu_read_lock (preempt_disabled) */ /* * 网桥钩子入口函数 */ /* PREROUTING --+--FORWARD-----POSTROUTING------+----OUTPUT | | | | INPUT */ struct sk_buff *br_handle_frame(struct net_bridge_port *p, struct sk_buff *skb) { const unsigned char *dest = eth_hdr(skb)->h_dest;/* 目的MAC地址 */ /* 检测源MAC合法性,源MAC不可为全0、多播或广播地址 * 即源MAC只能为确定的单播地址 */ if (!is_valid_ether_addr(eth_hdr(skb)->h_source)) goto drop; /* 组播包 */ /* 组播包是不需要NF_BR_PRE_ROUTING的,所以钩子直接到NF_BR_LOCAL_IN */ if (unlikely(is_link_local(dest))) { /* Pause frames shouldn't be passed up by driver anyway */ if (skb->protocol == htons(ETH_P_PAUSE)) goto drop; /* Process STP BPDU's through normal netif_receive_skb() path */ /* 网桥打开了STP功能 */ if (p->br->stp_enabled != BR_NO_STP) { if (NF_HOOK(PF_BRIDGE, NF_BR_LOCAL_IN, skb, skb->dev, NULL, br_handle_local_finish)) return NULL; else return skb; } } /* 网桥为转发或学习状态 */ switch (p->state) { case BR_STATE_FORWARDING: if (br_should_route_hook) { if (br_should_route_hook(&skb)) return skb; dest = eth_hdr(skb)->h_dest; } /* fall through */ case BR_STATE_LEARNING: if (!compare_ether_addr(p->br->dev->dev_addr, dest)) skb->pkt_type = PACKET_HOST; /* 网桥路由前钩子点 */ NF_HOOK(PF_BRIDGE, NF_BR_PRE_ROUTING, skb, skb->dev, NULL, br_handle_frame_finish); break; default: drop: kfree_skb(skb); } return NULL; } |
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