114 lines
2.5 KiB
C
114 lines
2.5 KiB
C
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#include <stdlib.h>
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#include <stdio.h>
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#include <unistd.h>
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#include <string.h>
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#include <sys/socket.h>
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#include <netinet/in.h>
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#include <arpa/inet.h>
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int guard(int n, char *err)
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{
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if (n == -1)
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{
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perror(err);
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exit(1);
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}
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return n;
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}
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int g_fd = 0;
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void printflag()
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{
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printf("Hello!");
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char *flag = getenv("IG_FLAG");
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send(g_fd, flag, strlen(flag), 0);
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send(g_fd, "\n", 1, 0);
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}
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int login(int fd)
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{
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g_fd = fd;
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char pw[32] = {0};
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char *pwd = "Enter the password:\n";
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char *correct = "Correct!\n";
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printf("%x\n",(long)*(&pw + 32 + 8));
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sprintf(pw, "%s\r\n", getenv("IG_PASSWORD"));
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char buf[32];
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send(fd, pwd, strlen(pwd), 0);
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ssize_t num_bytes_received = guard(recv(fd, buf, 96, 0), "Could not recv on TCP connection");
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if (num_bytes_received <2)
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return 0;
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//buf[num_bytes_received-2] = 0;
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if (strcmp(buf, pw))
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{
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return 0;
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}
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else
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{
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send(fd, correct, strlen(correct), 0);
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printflag(fd);
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return 1;
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}
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}
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int main(void)
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{
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char *wrong = "Wrong!\n";
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int opt = 1;
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int listen_fd = guard(socket(AF_INET, SOCK_STREAM, 0), "Could not create TCP socket");
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printf("Created new socket %d\n", listen_fd);
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struct sockaddr_in listen_addr = {0};
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listen_addr.sin_family = AF_INET;
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listen_addr.sin_addr.s_addr = htonl(INADDR_ANY);
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listen_addr.sin_port = htons(2345);
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guard(setsockopt(listen_fd, SOL_SOCKET, SO_REUSEADDR | SO_REUSEPORT,
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&opt, sizeof(opt)),
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"could not set opt");
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guard(bind(listen_fd, (struct sockaddr *)&listen_addr, sizeof(listen_addr)), "Could not bind");
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guard(listen(listen_fd, 100), "Could not listen on TCP socket");
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printf("Listening for connections on port %d\n", ntohs(listen_addr.sin_port));
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for (;;)
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{
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int conn_fd = accept(listen_fd, NULL, NULL);
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printf("Got new connection %d\n", conn_fd);
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if (guard(fork(), "Could not fork") == 0)
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{
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pid_t my_pid = getpid();
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printf("%d: forked\n", my_pid);
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char buf[100];
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sprintf(buf, "Pointer to printflag is %p\n", printflag);
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guard(send(conn_fd, buf, strlen(buf), 0), "Could not send to TCP connection");
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if (!login(conn_fd)) {
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send(conn_fd, wrong, strlen(wrong), 0);
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}
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printf("%d: received end-of-connection; closing connection and exiting\n", my_pid);
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guard(shutdown(conn_fd, SHUT_WR), "Could not shutdown TCP connection");
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guard(close(conn_fd), "Could not close TCP connection");
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exit(0);
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}
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else
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{
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// Child takes over connection; close it in parent
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close(conn_fd);
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}
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}
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return 0;
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}
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