mirror of https://github.com/torvalds/linux.git
107 lines
2.5 KiB
C
107 lines
2.5 KiB
C
// SPDX-License-Identifier: GPL-2.0
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#include <linux/bpf.h>
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#include <bpf/bpf_helpers.h>
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#include <linux/if_ether.h>
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#include <linux/in.h>
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#include <linux/ip.h>
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#include <linux/udp.h>
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#include <linux/pkt_cls.h>
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long change_tail_ret = 1;
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static __always_inline struct iphdr *parse_ip_header(struct __sk_buff *skb, int *ip_proto)
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{
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void *data_end = (void *)(long)skb->data_end;
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void *data = (void *)(long)skb->data;
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struct ethhdr *eth = data;
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struct iphdr *iph;
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/* Verify Ethernet header */
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if ((void *)(data + sizeof(*eth)) > data_end)
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return NULL;
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/* Skip Ethernet header to get to IP header */
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iph = (void *)(data + sizeof(struct ethhdr));
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/* Verify IP header */
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if ((void *)(data + sizeof(struct ethhdr) + sizeof(*iph)) > data_end)
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return NULL;
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/* Basic IP header validation */
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if (iph->version != 4) /* Only support IPv4 */
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return NULL;
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if (iph->ihl < 5) /* Minimum IP header length */
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return NULL;
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*ip_proto = iph->protocol;
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return iph;
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}
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static __always_inline struct udphdr *parse_udp_header(struct __sk_buff *skb, struct iphdr *iph)
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{
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void *data_end = (void *)(long)skb->data_end;
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void *hdr = (void *)iph;
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struct udphdr *udp;
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/* Calculate UDP header position */
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udp = hdr + (iph->ihl * 4);
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hdr = (void *)udp;
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/* Verify UDP header bounds */
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if ((void *)(hdr + sizeof(*udp)) > data_end)
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return NULL;
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return udp;
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}
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SEC("tc/ingress")
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int change_tail(struct __sk_buff *skb)
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{
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int len = skb->len;
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struct udphdr *udp;
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struct iphdr *iph;
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void *data_end;
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char *payload;
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int ip_proto;
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bpf_skb_pull_data(skb, len);
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data_end = (void *)(long)skb->data_end;
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iph = parse_ip_header(skb, &ip_proto);
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if (!iph)
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return TCX_PASS;
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if (ip_proto != IPPROTO_UDP)
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return TCX_PASS;
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udp = parse_udp_header(skb, iph);
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if (!udp)
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return TCX_PASS;
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payload = (char *)udp + (sizeof(struct udphdr));
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if (payload + 1 > (char *)data_end)
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return TCX_PASS;
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if (payload[0] == 'T') { /* Trim the packet */
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change_tail_ret = bpf_skb_change_tail(skb, len - 1, 0);
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if (!change_tail_ret)
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bpf_skb_change_tail(skb, len, 0);
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return TCX_PASS;
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} else if (payload[0] == 'G') { /* Grow the packet */
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change_tail_ret = bpf_skb_change_tail(skb, len + 1, 0);
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if (!change_tail_ret)
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bpf_skb_change_tail(skb, len, 0);
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return TCX_PASS;
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} else if (payload[0] == 'E') { /* Error */
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change_tail_ret = bpf_skb_change_tail(skb, 65535, 0);
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return TCX_PASS;
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} else if (payload[0] == 'Z') { /* Zero */
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change_tail_ret = bpf_skb_change_tail(skb, 0, 0);
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return TCX_PASS;
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}
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return TCX_DROP;
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}
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char _license[] SEC("license") = "GPL";
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