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