sys_getdents filename extraction

gistfile1.txt

#include <dirent.h>
#include <fcntl.h>
#include <stdio.h>
#include <stdlib.h>
#include <sys/stat.h>
#include <sys/syscall.h>
#include <unistd.h>

struct linux_dirent {
	unsigned long d_ino;
	unsigned long d_off;
	unsigned short d_reclen;
	char d_name[];
};

int main()
{
	int fd, syscall_rv;
	char buffer[1024];

	if ((fd = open("./passwd/", O_RDONLY | O_DIRECTORY)) == -1) {
		printf("[!] open() failed\n");
		return -1;
	}

	if ((syscall_rv = syscall(SYS_getdents, fd, buffer, 1024)) == -1) {
		printf("[!] syscall failed()\n");
		return -1;
	}

	printf("[+] read %d bytes using SYS_getdents.\n", syscall_rv);
	printf("[+] start extraction of filenames.\n");

	for (size_t buffer_index = 0; buffer_index < syscall_rv; ) {
		// jump above d_ino, d_off and d_reclen with the offset 18:
		printf("%s\n", buffer + buffer_index + 18);

		// increment with d_reclen:
		buffer_index += *((unsigned short *) (buffer + buffer_index + 16));
	}

	return 0;
}