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35 lines
1.0 KiB
C
35 lines
1.0 KiB
C
/* TC-BPF program that enforce MTU based on BPF-helper
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*/
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#include <linux/bpf.h>
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#include <bpf/bpf_helpers.h>
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/* Testing BPF-helper that is not upstream yet, requires us to define
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* its call signature manually, which will only match our devel kernel.
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*
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* Generated signatur via command in kernel devel tree:
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* ./scripts/bpf_helpers_doc.py --header | grep bpf_check_mtu
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*/
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static int (*bpf_check_mtu)(void *ctx, __u32 ifindex, __u32 *mtu_len, __s32 len_diff, __u64 flags) = (void *) 163;
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enum bpf_check_mtu_flags {
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BPF_MTU_CHK_SEGS = (1U << 0),
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};
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SEC("classifier") int tc_check_mtu(struct __sk_buff *skb)
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{
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/* Main point behind this test is using flag BPF_MTU_CHK_SEGS,
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* because is will len check individual GSO/GRO segments in an SKB.
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* BPF and kernel often skip checks if "skb_is_gso()".
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*/
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__u64 flags = BPF_MTU_CHK_SEGS;
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__u32 mtu_len = 0;
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__s32 delta = 0;
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if (bpf_check_mtu(skb, 0, &mtu_len, delta, flags)) {
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return BPF_DROP;
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}
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return BPF_OK;
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}
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char _license[] SEC("license") = "GPL";
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