vuln.c

#include <unistd.h>
#include <stdlib.h>
#include <stdio.h>
#include <fcntl.h>
#include <string.h>

void vuln(const char* content, int size) {
	if (size < 12)
		return;
	if (content[0] == 'G' && content[1] == 'O' && content[2] == 'T' &&
	    content[3] == 'T' && content[4] == 'A' && content[5] == 'G' &&
	    content[6] == 'O' && content[7] == 'F' && content[8] == 'A' &&
	    content[9] == 'S' && content[10] == 'T' && content[11] == '!')
	{
		*(int*)(0xDEADBEEF) = 0x41414141;
	}
}

int main(int argc, char** argv) {
	if (argc < 2) {
		printf("usage: %s filename\n", argv[0]);
		return EXIT_FAILURE;
	}

	int fd = open(argv[1], O_RDONLY);
	if (fd == -1) {
		perror("error opening file");
		exit(EXIT_FAILURE);
	}

	char data[1024];
	size_t bytes_read = read(fd, data, sizeof(data));
	if (bytes_read == -1) {
		perror("error reading file");
		exit(EXIT_FAILURE);
	}

	close(fd);

	vuln(data, bytes_read);
	return 0;
}