50 lines
1.2 KiB
C
50 lines
1.2 KiB
C
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// SPDX-License-Identifier: GPL-2.0
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// Copyright (c) 2018 Facebook
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#include <linux/stddef.h>
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#include <linux/bpf.h>
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#include <sys/socket.h>
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#include "bpf_helpers.h"
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#include "bpf_endian.h"
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#define SRC1_IP4 0xAC100001U /* 172.16.0.1 */
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#define SRC2_IP4 0x00000000U
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#define SRC_REWRITE_IP4 0x7f000004U
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#define DST_IP4 0xC0A801FEU /* 192.168.1.254 */
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#define DST_REWRITE_IP4 0x7f000001U
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#define DST_PORT 4040
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#define DST_REWRITE_PORT4 4444
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int _version SEC("version") = 1;
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SEC("cgroup/sendmsg4")
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int sendmsg_v4_prog(struct bpf_sock_addr *ctx)
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{
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if (ctx->type != SOCK_DGRAM)
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return 0;
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/* Rewrite source. */
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if (ctx->msg_src_ip4 == bpf_htonl(SRC1_IP4) ||
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ctx->msg_src_ip4 == bpf_htonl(SRC2_IP4)) {
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ctx->msg_src_ip4 = bpf_htonl(SRC_REWRITE_IP4);
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} else {
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/* Unexpected source. Reject sendmsg. */
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return 0;
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}
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/* Rewrite destination. */
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if ((ctx->user_ip4 >> 24) == (bpf_htonl(DST_IP4) >> 24) &&
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ctx->user_port == bpf_htons(DST_PORT)) {
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ctx->user_ip4 = bpf_htonl(DST_REWRITE_IP4);
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ctx->user_port = bpf_htons(DST_REWRITE_PORT4);
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} else {
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/* Unexpected source. Reject sendmsg. */
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return 0;
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}
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return 1;
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}
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char _license[] SEC("license") = "GPL";
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