(1) 在inet_init中注册了类型为ETH_P_IP协议的数据包的回调ip_rcv
(2) 当二层数据包接收完毕，会调用netif_receive_skb根据协议进行向上层分发
(3) 类型为ETH_P_IP类型的数据包，被传递到三层，调用ip_rcv函数
(4) ip_rcv完成基本的校验和处理工作后，经过PRE_ROUTING钩子点
(5) 经过PRE_ROUTING钩子点之后，调用ip_rcv_finish完成数据包接收，包括选项处理，路由查询，并且根据路由决定数据包是发往本机还是转发
1 static struct packet_type ip_packet_type __read_mostly = {
2 .type = cpu_to_be16(ETH_P_IP),
3 .func = ip_rcv,
4 };
1 /*
2 * Main IP Receive routine.
3 */
4 int ip_rcv(struct sk_buff *skb, struct net_device *dev, struct packet_type *pt, struct net_device *orig_dev)
5 {
6 const struct iphdr *iph;
7 struct net *net;
8 u32 len;
9
10 /* When the interface is in promisc. mode, drop all the crap
11 * that it receives, do not try to analyse it.
12 */
13 /* 混杂模式下，非本机包 */
14 if (skb->pkt_type == PACKET_OTHERHOST)
15 goto drop;
16
17
18 /* 获取net */
19 net = dev_net(dev);
20 __IP_UPD_PO_STATS(net, IPSTATS_MIB_IN, skb->len);
21
22 /* 检查skb共享 */
23 skb = skb_share_check(skb, GFP_ATOMIC);
24 if (!skb) {
25 __IP_INC_STATS(net, IPSTATS_MIB_INDISCARDS);
26 goto out;
27 }
28
29 /* 测试是否可以取得ip头 */
30 if (!pskb_may_pull(skb, sizeof(struct iphdr)))
31 goto inhdr_error;
32
33 /* 取ip头 */
34 iph = ip_hdr(skb);
35
36 /*
37 * RFC1122: 3.2.1.2 MUST silently discard any IP frame that fails the checksum.
38 *
39 * Is the datagram acceptable?
40 *
41 * 1. Length at least the size of an ip header
42 * 2. Version of 4
43 * 3. Checksums correctly. [Speed optimisation for later, skip loopback checksums]
44 * 4. Doesn‘t have a bogus length
45 */
46
47 /* 头部长度不足20 或者版本不是4 */
48 if (iph->ihl < 5 || iph->version != 4)
49 goto inhdr_error;
50
51 BUILD_BUG_ON(IPSTATS_MIB_ECT1PKTS != IPSTATS_MIB_NOECTPKTS + INET_ECN_ECT_1);
52 BUILD_BUG_ON(IPSTATS_MIB_ECT0PKTS != IPSTATS_MIB_NOECTPKTS + INET_ECN_ECT_0);
53 BUILD_BUG_ON(IPSTATS_MIB_CEPKTS != IPSTATS_MIB_NOECTPKTS + INET_ECN_CE);
54 __IP_ADD_STATS(net,
55 IPSTATS_MIB_NOECTPKTS + (iph->tos & INET_ECN_MASK),
56 max_t(unsigned short, 1, skb_shinfo(skb)->gso_segs));
57
58 /* 测试实际应取的ip头 */
59 if (!pskb_may_pull(skb, iph->ihl*4))
60 goto inhdr_error;
61
62 /* 取ip头 */
63 iph = ip_hdr(skb);
64
65 /* 校验和错误 */
66 if (unlikely(ip_fast_csum((u8 *)iph, iph->ihl)))
67 goto csum_error;
68
69 /* 取总长度 */
70 len = ntohs(iph->tot_len);
71
72 /* skb长度比ip包总长度小 */
73 if (skb->len < len) {
74 __IP_INC_STATS(net, IPSTATS_MIB_INTRUNCATEDPKTS);
75 goto drop;
76 }
77 /* 比头部长度还小 */
78 else if (len < (iph->ihl*4))
79 goto inhdr_error;
80
81 /* Our transport medium may have padded the buffer out. Now we know it
82 * is IP we can trim to the true length of the frame.
83 * Note this now means skb->len holds ntohs(iph->tot_len).
84 */
85 /* 设置总长度为ip包的长度 */
86 if (pskb_trim_rcsum(skb, len)) {
87 __IP_INC_STATS(net, IPSTATS_MIB_INDISCARDS);
88 goto drop;
89 }
90
91 /* 取得传输层头部 */
92 skb->transport_header = skb->network_header + iph->ihl*4;
93
94 /* Remove any debris in the socket control block */
95 /* 重置cb */
96 memset(IPCB(skb), 0, sizeof(struct inet_skb_parm));
97
98 /* 保存输入设备信息 */
99 IPCB(skb)->iif = skb->skb_iif;
100
101 /* Must drop socket now because of tproxy. */
102 skb_orphan(skb);
103
104 /* 经过PRE_ROUTING钩子点 */
105 return NF_HOOK(NFPROTO_IPV4, NF_INET_PRE_ROUTING,
106 net, NULL, skb, dev, NULL,
107 ip_rcv_finish);
108
109 csum_error:
110 __IP_INC_STATS(net, IPSTATS_MIB_CSUMERRORS);
111 inhdr_error:
112 __IP_INC_STATS(net, IPSTATS_MIB_INHDRERRORS);
113 drop:
114 kfree_skb(skb);
115 out:
116 return NET_RX_DROP;
117 }
static int ip_rcv_finish(struct net *net, struct sock *sk, struct sk_buff *skb)
{
const struct iphdr *iph = ip_hdr(skb);
struct rtable *rt;
struct net_device *dev = skb->dev;
void (*edemux)(struct sk_buff *skb);
/* if ingress device is enslaved to an L3 master device pass the
* skb to its handler for processing
*/
skb = l3mdev_ip_rcv(skb);
if (!skb)
return NET_RX_SUCCESS;
/*
启用了early_demux
skb路由缓存为空
skb的sock为空
不是分片包
*/
if (net->ipv4.sysctl_ip_early_demux &&
!skb_dst(skb) &&
!skb->sk &&
!ip_is_fragment(iph)) {
const struct net_protocol *ipprot;
/* 找到上层协议 */
int protocol = iph->protocol;
/* 获取协议对应的prot */
ipprot = rcu_dereference(inet_protos[protocol]);
/* 找到early_demux函数，如tcp_v4_early_demux */
if (ipprot && (edemux = READ_ONCE(ipprot->early_demux))) {
/* 调用该函数，将路由信息缓存到skb->refdst */
edemux(skb);
/* must reload iph, skb->head might have changed */
/* 重新取ip头 */
iph = ip_hdr(skb);
}
}
/*
* Initialise the virtual path cache for the packet. It describes
* how the packet travels inside Linux networking.
*/
/* 校验路由失败 */
if (!skb_valid_dst(skb)) {
/* 查路由 */
int err = ip_route_input_noref(skb, iph->daddr, iph->saddr,
iph->tos, dev);
if (unlikely(err)) {
if (err == -EXDEV)
__NET_INC_STATS(net, LINUX_MIB_IPRPFILTER);
goto drop;
}
}
#ifdef CONFIG_IP_ROUTE_CLASSID
if (unlikely(skb_dst(skb)->tclassid)) {
struct ip_rt_acct *st = this_cpu_ptr(ip_rt_acct);
u32 idx = skb_dst(skb)->tclassid;
st[idx&0xFF].o_packets++;
st[idx&0xFF].o_bytes += skb->len;
st[(idx>>16)&0xFF].i_packets++;
st[(idx>>16)&0xFF].i_bytes += skb->len;
}
#endif
/* 处理ip选项 */
if (iph->ihl > 5 && ip_rcv_options(skb))
goto drop;
/* 找到路由缓存项 */
rt = skb_rtable(skb);
if (rt->rt_type == RTN_MULTICAST) {
__IP_UPD_PO_STATS(net, IPSTATS_MIB_INMCAST, skb->len);
} else if (rt->rt_type == RTN_BROADCAST) {
__IP_UPD_PO_STATS(net, IPSTATS_MIB_INBCAST, skb->len);
} else if (skb->pkt_type == PACKET_BROADCAST ||
skb->pkt_type == PACKET_MULTICAST) {
struct in_device *in_dev = __in_dev_get_rcu(dev);
/* RFC 1122 3.3.6:
*
* When a host sends a datagram to a link-layer broadcast
* address, the IP destination address MUST be a legal IP
* broadcast or IP multicast address.
*
* A host SHOULD silently discard a datagram that is received
* via a link-layer broadcast (see Section 2.4) but does not
* specify an IP multicast or broadcast destination address.
*
* This doesn‘t explicitly say L2 *broadcast*, but broadcast is
* in a way a form of multicast and the most common use case for
* this is 802.11 protecting against cross-station spoofing (the
* so-called "hole-196" attack) so do it for both.
*/
if (in_dev &&
IN_DEV_ORCONF(in_dev, DROP_UNICAST_IN_L2_MULTICAST))
goto drop;
}
/* 调用路由项的input函数，可能为ip_local_deliver或者ip_forward */
return dst_input(skb);
drop:
kfree_skb(skb);
return NET_RX_DROP;
}
时间： 2024-10-30 02:14:43