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cf9b1199de
This example shows using a kprobe to act as a dnat mechanism to divert traffic for arbitrary endpoints. It rewrite the arguments to a syscall while they're still in userspace, and before the syscall has a chance to copy the argument into kernel space. Although this is an example, it also acts as a test because the mapped address is 255.255.255.255:555 -> real address, and that's not a legal address to connect to. If the helper is broken, the example will fail on the intermediate steps, as well as the final step to verify the rewrite of userspace memory succeeded. Signed-off-by: Sargun Dhillon <sargun@sargun.me> Cc: Alexei Starovoitov <ast@kernel.org> Cc: Daniel Borkmann <daniel@iogearbox.net> Acked-by: Alexei Starovoitov <ast@kernel.org> Signed-off-by: David S. Miller <davem@davemloft.net>
78 lines
2.4 KiB
C
78 lines
2.4 KiB
C
#include <stdio.h>
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#include <assert.h>
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#include <linux/bpf.h>
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#include <unistd.h>
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#include "libbpf.h"
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#include "bpf_load.h"
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#include <sys/socket.h>
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#include <string.h>
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#include <netinet/in.h>
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#include <arpa/inet.h>
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int main(int ac, char **argv)
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{
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int serverfd, serverconnfd, clientfd;
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socklen_t sockaddr_len;
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struct sockaddr serv_addr, mapped_addr, tmp_addr;
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struct sockaddr_in *serv_addr_in, *mapped_addr_in, *tmp_addr_in;
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char filename[256];
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char *ip;
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serv_addr_in = (struct sockaddr_in *)&serv_addr;
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mapped_addr_in = (struct sockaddr_in *)&mapped_addr;
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tmp_addr_in = (struct sockaddr_in *)&tmp_addr;
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snprintf(filename, sizeof(filename), "%s_kern.o", argv[0]);
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if (load_bpf_file(filename)) {
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printf("%s", bpf_log_buf);
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return 1;
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}
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assert((serverfd = socket(AF_INET, SOCK_STREAM, 0)) > 0);
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assert((clientfd = socket(AF_INET, SOCK_STREAM, 0)) > 0);
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/* Bind server to ephemeral port on lo */
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memset(&serv_addr, 0, sizeof(serv_addr));
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serv_addr_in->sin_family = AF_INET;
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serv_addr_in->sin_port = 0;
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serv_addr_in->sin_addr.s_addr = htonl(INADDR_LOOPBACK);
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assert(bind(serverfd, &serv_addr, sizeof(serv_addr)) == 0);
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sockaddr_len = sizeof(serv_addr);
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assert(getsockname(serverfd, &serv_addr, &sockaddr_len) == 0);
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ip = inet_ntoa(serv_addr_in->sin_addr);
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printf("Server bound to: %s:%d\n", ip, ntohs(serv_addr_in->sin_port));
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memset(&mapped_addr, 0, sizeof(mapped_addr));
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mapped_addr_in->sin_family = AF_INET;
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mapped_addr_in->sin_port = htons(5555);
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mapped_addr_in->sin_addr.s_addr = inet_addr("255.255.255.255");
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assert(!bpf_update_elem(map_fd[0], &mapped_addr, &serv_addr, BPF_ANY));
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assert(listen(serverfd, 5) == 0);
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ip = inet_ntoa(mapped_addr_in->sin_addr);
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printf("Client connecting to: %s:%d\n",
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ip, ntohs(mapped_addr_in->sin_port));
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assert(connect(clientfd, &mapped_addr, sizeof(mapped_addr)) == 0);
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sockaddr_len = sizeof(tmp_addr);
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ip = inet_ntoa(tmp_addr_in->sin_addr);
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assert((serverconnfd = accept(serverfd, &tmp_addr, &sockaddr_len)) > 0);
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printf("Server received connection from: %s:%d\n",
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ip, ntohs(tmp_addr_in->sin_port));
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sockaddr_len = sizeof(tmp_addr);
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assert(getpeername(clientfd, &tmp_addr, &sockaddr_len) == 0);
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ip = inet_ntoa(tmp_addr_in->sin_addr);
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printf("Client's peer address: %s:%d\n",
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ip, ntohs(tmp_addr_in->sin_port));
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/* Is the server's getsockname = the socket getpeername */
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assert(memcmp(&serv_addr, &tmp_addr, sizeof(struct sockaddr_in)) == 0);
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return 0;
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}
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