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git.proxmox.com Git - mirror_ubuntu-jammy-kernel.git/blob - samples/bpf/xdp_adjust_tail_kern.c
1 /* SPDX-License-Identifier: GPL-2.0
2 * Copyright (c) 2018 Facebook
4 * This program is free software; you can redistribute it and/or
5 * modify it under the terms of version 2 of the GNU General Public
6 * License as published by the Free Software Foundation.
8 * This program shows how to use bpf_xdp_adjust_tail() by
9 * generating ICMPv4 "packet to big" (unreachable/ df bit set frag needed
10 * to be more preice in case of v4)" where receiving packets bigger then
13 #define KBUILD_MODNAME "foo"
14 #include <uapi/linux/bpf.h>
16 #include <linux/if_ether.h>
17 #include <linux/if_packet.h>
18 #include <linux/if_vlan.h>
20 #include <linux/icmp.h>
21 #include "bpf_helpers.h"
23 #define DEFAULT_TTL 64
24 #define MAX_PCKT_SIZE 600
25 #define ICMP_TOOBIG_SIZE 98
26 #define ICMP_TOOBIG_PAYLOAD_SIZE 92
28 struct bpf_map_def
SEC("maps") icmpcnt
= {
29 .type
= BPF_MAP_TYPE_ARRAY
,
30 .key_size
= sizeof(__u32
),
31 .value_size
= sizeof(__u64
),
35 static __always_inline
void count_icmp(void)
40 icmp_count
= bpf_map_lookup_elem(&icmpcnt
, &key
);
45 static __always_inline
void swap_mac(void *data
, struct ethhdr
*orig_eth
)
50 memcpy(eth
->h_source
, orig_eth
->h_dest
, ETH_ALEN
);
51 memcpy(eth
->h_dest
, orig_eth
->h_source
, ETH_ALEN
);
52 eth
->h_proto
= orig_eth
->h_proto
;
55 static __always_inline __u16
csum_fold_helper(__u32 csum
)
57 return ~((csum
& 0xffff) + (csum
>> 16));
60 static __always_inline
void ipv4_csum(void *data_start
, int data_size
,
63 *csum
= bpf_csum_diff(0, 0, data_start
, data_size
, *csum
);
64 *csum
= csum_fold_helper(*csum
);
67 static __always_inline
int send_icmp4_too_big(struct xdp_md
*xdp
)
69 int headroom
= (int)sizeof(struct iphdr
) + (int)sizeof(struct icmphdr
);
71 if (bpf_xdp_adjust_head(xdp
, 0 - headroom
))
73 void *data
= (void *)(long)xdp
->data
;
74 void *data_end
= (void *)(long)xdp
->data_end
;
76 if (data
+ (ICMP_TOOBIG_SIZE
+ headroom
) > data_end
)
79 struct iphdr
*iph
, *orig_iph
;
80 struct icmphdr
*icmp_hdr
;
81 struct ethhdr
*orig_eth
;
85 orig_eth
= data
+ headroom
;
86 swap_mac(data
, orig_eth
);
87 off
+= sizeof(struct ethhdr
);
89 off
+= sizeof(struct iphdr
);
90 icmp_hdr
= data
+ off
;
91 off
+= sizeof(struct icmphdr
);
92 orig_iph
= data
+ off
;
93 icmp_hdr
->type
= ICMP_DEST_UNREACH
;
94 icmp_hdr
->code
= ICMP_FRAG_NEEDED
;
95 icmp_hdr
->un
.frag
.mtu
= htons(MAX_PCKT_SIZE
-sizeof(struct ethhdr
));
96 icmp_hdr
->checksum
= 0;
97 ipv4_csum(icmp_hdr
, ICMP_TOOBIG_PAYLOAD_SIZE
, &csum
);
98 icmp_hdr
->checksum
= csum
;
99 iph
->ttl
= DEFAULT_TTL
;
100 iph
->daddr
= orig_iph
->saddr
;
101 iph
->saddr
= orig_iph
->daddr
;
104 iph
->protocol
= IPPROTO_ICMP
;
106 iph
->tot_len
= htons(
107 ICMP_TOOBIG_SIZE
+ headroom
- sizeof(struct ethhdr
));
110 ipv4_csum(iph
, sizeof(struct iphdr
), &csum
);
117 static __always_inline
int handle_ipv4(struct xdp_md
*xdp
)
119 void *data_end
= (void *)(long)xdp
->data_end
;
120 void *data
= (void *)(long)xdp
->data
;
121 int pckt_size
= data_end
- data
;
124 if (pckt_size
> MAX_PCKT_SIZE
) {
125 offset
= pckt_size
- ICMP_TOOBIG_SIZE
;
126 if (bpf_xdp_adjust_tail(xdp
, 0 - offset
))
128 return send_icmp4_too_big(xdp
);
134 int _xdp_icmp(struct xdp_md
*xdp
)
136 void *data_end
= (void *)(long)xdp
->data_end
;
137 void *data
= (void *)(long)xdp
->data
;
138 struct ethhdr
*eth
= data
;
141 if (eth
+ 1 > data_end
)
144 h_proto
= eth
->h_proto
;
146 if (h_proto
== htons(ETH_P_IP
))
147 return handle_ipv4(xdp
);
152 char _license
[] SEC("license") = "GPL";