61 lines
1.3 KiB
C
61 lines
1.3 KiB
C
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#include <stdio.h>
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#include <stdlib.h>
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#include <unistd.h>
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#include <fcntl.h>
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#include <sys/stat.h>
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#define MATH_PROBLEMS 10000
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int take_test() {
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int urand = open("/dev/urandom", O_RDONLY);
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if (!urand) return 1;
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unsigned char urand_byte;
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for (int i=0; i<MATH_PROBLEMS; i++) {
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if (read(urand, &urand_byte, 1) != 1) return 1;
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int a = urand_byte & 0xf;
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int b = urand_byte >> 4;
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printf("Question %d: %d * %d = ", i+1, a, b);
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int ans;
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if (scanf("%d", &ans) != 1) return 1;
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if (ans != a * b) return 1;
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}
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close(urand);
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return 0;
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}
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int check_id() {
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printf("Checking your student ID...\n\n");
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sleep(1);
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struct stat real, given;
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if (stat("/proc/1/fd/0", &real)) return 1;
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if (fstat(0, &given)) return 1;
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if (real.st_dev != given.st_dev) return 1;
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if (real.st_ino != given.st_ino) return 1;
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return 0;
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}
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int main() {
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setreuid(geteuid(), getuid());
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setvbuf(stdout, NULL, _IONBF, 0);
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printf("Welcome to the MATH 101 final exam.\n");
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if (check_id()) {
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printf("The proctor kicks you out for pretending to be a student.\n");
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return 1;
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}
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printf("The test begins now. You have three hours.\n\n");
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alarm(3 * 60 * 60);
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if (take_test()) {
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printf("You have failed the test.\n");
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return 1;
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}
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setreuid(getuid(), getuid());
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system("cat /home/ctf/flag");
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return 0;
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}
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