woody-woodpacker/srcs/woody.c

#include "../includes/woody.h"

int elf_magic_numbers(char *str)
{
	return (!ft_strncmp(str, ELFMAG, SELFMAG));
}

int save_elf(char *path, char *file, unsigned long int size)
{
	int fd = open(path, O_CREAT | O_WRONLY | O_TRUNC, 0755);
    if (fd == -1) {
		ft_printf("Error: Failed to create new file \'%s\'\n", path);
		return EXIT_FAILURE;
    }

    if (write(fd, file, size) == -1) {
        close(fd);
        ft_printf("Error: Failed to write new file \'%s\'\n", path);
        return EXIT_FAILURE;
    }

    if (close(fd) == -1) {
		ft_printf("Error: Failed to close new file \'%s\'\n", path);
        return EXIT_FAILURE;
    }
	return EXIT_SUCCESS;
}

int	get_load_segment(t_elf_content *woody, int start, bool executable)
{
	for (int i = start; i < woody->Ehdr->e_phnum; i++)
	{
		if (woody->Phdr[i].p_type == PT_LOAD)
		{
			if (executable)
			{
				if (woody->Phdr[i].p_flags & PF_X)
					return i;
			}
			else
				return i;
		}
	}
	return -1;
}

void offset_sections(t_elf_content *woody, unsigned int from, unsigned int offset_ammount)
{
	for (int i = 0; i < woody->Ehdr->e_phnum; i++)
	{
		if (woody->Phdr[i].p_offset > from)
			woody->Phdr[i].p_offset += offset_ammount;
	}
	for (int i = 0; i < woody->Ehdr->e_shnum; i++)
	{
		if (woody->Shdr[i].sh_offset > from)
			woody->Shdr[i].sh_offset += offset_ammount;
	}
}

size_t	create_codecave(t_elf_content *woody, Elf64_Phdr *load_segment, t_payload *payload)
{
	const unsigned int page_size = 4096; // getpagesize(); not authorized
	unsigned int padding_size = ((payload->len / page_size) + 1) * page_size;
	unsigned int codecave_start = load_segment->p_offset + load_segment->p_filesz;
	offset_sections(woody, codecave_start, padding_size);
	char *new_woody = malloc(woody->file_size + padding_size);
	if (!new_woody)
		return 0;
	ft_memcpy(new_woody, woody->file, codecave_start);
	ft_bzero(new_woody + codecave_start, padding_size);
	ft_memcpy(new_woody + codecave_start + padding_size,  woody->file + codecave_start, woody->file_size - codecave_start);
	munmap(woody->file, woody->file_size);
	woody->file = new_woody;
	woody->file_size += padding_size;
	woody->Ehdr = (Elf64_Ehdr *)new_woody;
	woody->Phdr = (Elf64_Phdr *)fetch(woody->file, woody->file_size, woody->Ehdr->e_phoff, sizeof(Elf64_Phdr));
	woody->Shdr = (Elf64_Shdr *)fetch(woody->file, woody->file_size, woody->Ehdr->e_shoff, sizeof(Elf64_Shdr));
	return codecave_start;
}

t_payload *get_payload()
{
	t_payload *payload = malloc(sizeof(t_payload));
	if (!payload)
		return NULL;
	char buffer[1024];
	int fd = open("payload", O_RDONLY);
	if (fd == -1) {
		perror("error opening payload");
		free(payload);
		exit(1);
	}
	payload->len = read(fd, buffer, 1024);
	payload->payload = malloc(sizeof(char) * payload->len);
	ft_memcpy(payload->payload, buffer, payload->len);
	return payload;
}

int	insert_payload(t_elf_content *woody, t_payload *payload, size_t payload_position)
{
	char *ptr_jmp = ft_strnstr_nullterminated(payload->payload, JUMP, payload->len);
	char *ptr_text_section = ft_strnstr_nullterminated(payload->payload, TEXT_OFFSET, payload->len);
	char *ptr_section_size = ft_strnstr_nullterminated(payload->payload, SECTION_SIZE, payload->len);
	if (ptr_jmp && ptr_text_section && ptr_section_size)
	{
		printf("test a jumo = %ld\n", ptr_jmp - payload->payload);
		printf("test a jumo = %ld\n", ptr_jmp - payload->payload + sizeof(JUMP));
		printf("jump base = %ld\n", payload->len);
		printf("the jump = %ld\n", payload->len - 16);

		int32_t jmp_index = ptr_jmp - payload->payload;
		int32_t jump_value = ((payload_position + jmp_index + 5) - woody->Ehdr->e_entry) * -1; // 5 = JUMP SIZE (OPCODE + 4 bytes operand)
		ft_memcpy(&payload->payload[jmp_index + 1], &jump_value, sizeof(jump_value));

		int64_t text_index = ptr_text_section - payload->payload;
		int64_t text_value = (payload_position - woody->text_section->sh_offset + text_index - 1) * -1;
		text_value = 0;
		ft_memcpy(&payload->payload[text_index], &text_value, sizeof(text_value));

		int64_t section_index = ptr_section_size - payload->payload;
		int64_t section_value = (payload_position - woody->text_section->sh_size + section_index - 1) * -1;
		ft_memcpy(&payload->payload[section_index], &section_value, sizeof(section_value));

		ft_memcpy(woody->file + payload_position, payload->payload, payload->len);
		printf("Old entry : %ld (%lx)\n", woody->Ehdr->e_entry, woody->Ehdr->e_entry);
		printf("Code cave start = %ld (%lx)\n", payload_position, payload_position);
		printf("Payload size = %ld (%lx)\n", payload->len, payload->len);
		printf("Backward offset = %d (%x)(%x)\n", jump_value, jump_value, -jump_value);
		return EXIT_SUCCESS;
	}
	return EXIT_FAILURE;
}

void	inject(t_elf_content *woody)
{
	t_payload *payload = get_payload();
	int i = get_load_segment(woody, 0, true);
	int j = get_load_segment(woody, i + 1, false);

	size_t code_cave_size = woody->Phdr[j].p_offset - (woody->Phdr[i].p_offset + woody->Phdr[i].p_filesz);
	size_t payload_position;
	printf("load position = : %ld (%lx)\n", woody->Phdr[i].p_offset, woody->Phdr[i].p_offset);
	printf("load size = : %ld (%lx)\n", woody->Phdr[i].p_filesz, woody->Phdr[i].p_filesz);
	if (code_cave_size > payload->len) // inverse here to test the other technique
	{
		payload_position = woody->Phdr[i].p_offset + woody->Phdr[i].p_memsz;
		printf("Code_cave_size = %ld (%lx)\n", code_cave_size, code_cave_size);
	}
	else
	{
		payload_position = create_codecave(woody, &woody->Phdr[i], payload);
	}
	insert_payload(woody, payload, payload_position);

	woody->Ehdr->e_entry = payload_position;
	woody->Phdr[i].p_filesz += payload->len;
	woody->Phdr[i].p_memsz += payload->len;
	woody->Phdr[i].p_flags = PF_X | PF_W | PF_R;
	woody->text_section->sh_size += payload->len;
	printf("New entry = %ld (%lx)\n", woody->Ehdr->e_entry, woody->Ehdr->e_entry);
}

int is_special_section_indice(uint16_t section_index) {
  return (section_index == SHN_LOPROC || section_index == SHN_BEFORE ||
          section_index == SHN_AFTER || section_index == SHN_HIPROC ||
          section_index == SHN_LOOS || section_index == SHN_HIOS ||
          section_index == SHN_ABS || section_index == SHN_COMMON ||
          section_index == SHN_XINDEX || section_index == SHN_HIRESERVE);
}

int get_elf_sections(t_elf_content *woody)
{
	woody->Ehdr = (Elf64_Ehdr *)fetch(woody->file, woody->file_size, 0, sizeof(Elf64_Ehdr));
	if (!woody->Ehdr || !elf_magic_numbers(woody->file) || woody->Ehdr->e_ident[EI_CLASS] != ELFCLASS64)
	{
		ft_printf("Error: \'%s\' is not a valid 64-bit ELF file\n", woody->file_path);
		return EXIT_FAILURE;
	}
	woody->Phdr = (Elf64_Phdr *)fetch(woody->file, woody->file_size, woody->Ehdr->e_phoff, sizeof(Elf64_Phdr));

	woody->Shdr = (Elf64_Shdr *)fetch(woody->file, woody->file_size, woody->Ehdr->e_shoff, sizeof(Elf64_Shdr));
	if (!woody->Shdr|| !fetch(woody->file, woody->file_size, woody->Ehdr->e_shoff, woody->Ehdr->e_shnum * sizeof(Elf64_Shdr)))
		return EXIT_FAILURE;

	if (!fetch(woody->file, woody->file_size, woody->Ehdr->e_shoff + (woody->Ehdr->e_shstrndx * sizeof(Elf64_Shdr)), sizeof(Elf64_Shdr)))
	{
		return EXIT_FAILURE;
	}
	char *Sshstrtab = (char *)fetch(woody->file, woody->file_size, woody->Shdr[woody->Ehdr->e_shstrndx].sh_offset, 0);
	if (Sshstrtab == NULL)
	{
		return EXIT_FAILURE;
	}
	for (int j = 0; j < woody->Ehdr->e_shnum;j++)
	{
		if (woody->Shdr[j].sh_name > woody->Shdr[woody->Ehdr->e_shstrndx].sh_size) return EXIT_FAILURE;
    	if (woody->Shdr[j].sh_type == SHT_PROGBITS && woody->Shdr[j].sh_flags & SHF_EXECINSTR &&
        woody->Shdr[j].sh_flags & SHF_ALLOC &&
        Sshstrtab + woody->Shdr[j].sh_name < (char *)woody->file + woody->file_size &&
        !ft_strncmp(".text\0", Sshstrtab + woody->Shdr[j].sh_name, 6))
		{
			woody->text_section = &woody->Shdr[j];
 		    break;
		}
	}

	return EXIT_SUCCESS;
}

int prepare_injection(t_elf_content *woody)
{
	int elf_statut = get_elf_sections(woody);
	if (elf_statut)
		return elf_statut;
	inject(woody);
	// encrypt(woody->file, woody->text_section->sh_offset, woody->text_section->sh_size);
	char *woody_file;
	if (!(woody_file = malloc(woody->file_size)))
		return ft_put_error("Allocation error");
	ft_memcpy(woody_file, woody->file, woody->file_size);
	munmap(woody_file, woody->file_size);
	save_elf("woody", woody_file, woody->file_size);
	free(woody_file);
	return EXIT_SUCCESS;
}