mirror of
https://github.com/xdp-project/bpf-examples.git
synced 2024-05-06 15:54:53 +00:00
70 lines
1.6 KiB
C
70 lines
1.6 KiB
C
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#include <linux/bpf.h>
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#include <linux/in6.h>
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#include <bpf/bpf_helpers.h>
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#include <xdp/parsing_helpers.h>
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/* MTU is defined as L3 size (usually 1500 for Ethernet),
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* but remember TC (and XDP) operate at L2.
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*/
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//#define PKT_SIZE_L3 1500
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#define PKT_SIZE_L3 1501
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//#define PKT_SIZE_L3 1505
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//#define PKT_SIZE_L3 1600
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//#define PKT_SIZE_L3 20000
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//#define PKT_SIZE_L3 65535
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#define OFFSET sizeof(struct iphdr)
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#define ENCAP_TYPE BPF_F_ADJ_ROOM_ENCAP_L3_IPV4
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SEC("classifier") int tc_inc_pkt_sz(struct __sk_buff *skb)
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{
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volatile void *data, *data_end;
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int ret = BPF_DROP;
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struct ethhdr *eth;
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struct iphdr *iph;
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int extra_len;
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int len;
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/* Desired packet size at L2 */
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int pkt_size_l2 = PKT_SIZE_L3 + sizeof(*eth) ;
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data = (void *)(long)skb->data;
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data_end = (void *)(long)skb->data_end;
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eth = (struct ethhdr *)data;
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if (data + sizeof(*eth) > data_end)
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return BPF_DROP;
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/* Keep ARP resolution working */
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if (eth->h_proto == bpf_htons(ETH_P_ARP)) {
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ret = BPF_OK;
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goto out;
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}
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len = (data_end - data);
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extra_len = pkt_size_l2 - len;
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if (bpf_skb_adjust_room(skb, extra_len, BPF_ADJ_ROOM_MAC, ENCAP_TYPE))
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goto out;
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// TODO: Handle if bpf_skb_adjust_room() cannot increase size,
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// as it's only my patched kernel that drop the MTU check
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/* Most re-load after bpf_skb_adjust_room() */
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data = (void *)(long)skb->data;
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data_end = (void *)(long)skb->data_end;
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eth = (void *)data;
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iph = (void *)(eth +1);
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if (iph +1 > data_end)
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goto out;
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eth->h_proto = bpf_htons(ETH_P_IP);
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ret = BPF_OK;
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out:
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return ret;
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}
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char _license[] SEC("license") = "GPL";
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