| 1 | // SPDX-License-Identifier: GPL-2.0 |
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| 2 | #define BPF_NO_PRESERVE_ACCESS_INDEX |
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| 3 | #include <vmlinux.h> |
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| 4 | #include <bpf/bpf_core_read.h> |
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| 5 | #include <bpf/bpf_helpers.h> |
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| 6 | |
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| 7 | #define INLINE __always_inline |
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| 8 | |
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| 9 | #define skb_shorter(skb, len) ((void *)(long)(skb)->data + (len) > (void *)(long)skb->data_end) |
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| 10 | |
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| 11 | #define ETH_IPV4_TCP_SIZE (14 + sizeof(struct iphdr) + sizeof(struct tcphdr)) |
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| 12 | |
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| 13 | static INLINE struct iphdr *get_iphdr(struct __sk_buff *skb) |
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| 14 | { |
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| 15 | struct iphdr *ip = NULL; |
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| 16 | struct ethhdr *eth; |
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| 17 | |
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| 18 | if (skb_shorter(skb, ETH_IPV4_TCP_SIZE)) |
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| 19 | goto out; |
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| 20 | |
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| 21 | eth = (void *)(long)skb->data; |
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| 22 | ip = (void *)(eth + 1); |
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| 23 | |
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| 24 | out: |
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| 25 | return ip; |
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| 26 | } |
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| 27 | |
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| 28 | SEC("tc" ) |
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| 29 | int main_prog(struct __sk_buff *skb) |
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| 30 | { |
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| 31 | struct iphdr *ip = NULL; |
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| 32 | struct tcphdr *tcp; |
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| 33 | __u8 proto = 0; |
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| 34 | |
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| 35 | if (!(ip = get_iphdr(skb))) |
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| 36 | goto out; |
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| 37 | |
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| 38 | proto = ip->protocol; |
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| 39 | |
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| 40 | if (proto != IPPROTO_TCP) |
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| 41 | goto out; |
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| 42 | |
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| 43 | tcp = (void*)(ip + 1); |
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| 44 | if (tcp->dest != 0) |
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| 45 | goto out; |
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| 46 | if (!tcp) |
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| 47 | goto out; |
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| 48 | |
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| 49 | return tcp->urg_ptr; |
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| 50 | out: |
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| 51 | return -1; |
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| 52 | } |
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| 53 | char _license[] SEC("license" ) = "GPL" ; |
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| 54 | |
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