woody-woodpacker/srcs/woody.c

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

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

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;
}

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) {
		ft_put_error("Failed to open payload");
		free(payload);
		close(fd);
		return NULL;
	}
	payload->len = read(fd, buffer, 1024);
	if (payload->len == -1)
	{
		ft_put_error("Failed to read payload");
		free(payload);
		close(fd);
		return NULL;
	}
	close(fd);
	payload->payload = malloc(sizeof(char) * payload->len);
	if (!payload->payload)
	{
		ft_put_error("Allocation error");
		free(payload);
		return NULL;
	}
	ft_memcpy(payload->payload, buffer, payload->len);
	return payload;
}

int	insert_payload(t_elf_content *woody, t_payload *payload, size_t payload_position, int load_segment_index)
{
	char *ptr_jmp_value = ft_strnstr_nullterminated(payload->payload, JUMP_VALUE, payload->len);
	char *ptr_woody = ft_strnstr_nullterminated(payload->payload, WOODY, 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_value && ptr_woody && ptr_text_section && ptr_section_size)
	{
		int32_t woody_index = ptr_woody - payload->payload;
		int32_t jmp_index = ptr_jmp_value - sizeof(JUMP) - 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->Phdr[load_segment_index].p_offset + woody_index;
		ft_memcpy(&payload->payload[text_index], &text_value, sizeof(text_value));

		int64_t section_index = ptr_section_size - payload->payload;
		int64_t section_value = woody->Phdr[load_segment_index].p_memsz;
		ft_memcpy(&payload->payload[section_index], &section_value, sizeof(section_value));

		ft_memcpy(woody->file + payload_position, payload->payload, payload->len);
		return EXIT_SUCCESS;
	}
	return EXIT_FAILURE;
}

int	inject(t_elf_content *woody)
{
	t_payload *payload = get_payload();
	if (!payload)
		return EXIT_FAILURE;

	int i = get_load_segment(woody, 0, true);
	int j = get_load_segment(woody, i + 1, false);

	if (i == -1 || j != i + 1)
	{
		free(payload->payload);
		free(payload);
		return ft_put_error("PT_LOAD segment missing");
	}

	size_t code_cave_size = woody->Phdr[j].p_offset - (woody->Phdr[i].p_offset + woody->Phdr[i].p_filesz);
	size_t payload_position = woody->Phdr[i].p_offset + woody->Phdr[i].p_filesz;

	if (code_cave_size < (size_t)payload->len)
	{
		free(payload->payload);
		free(payload);
		return ft_put_error("Unable to insert payload, not enough space for code cave");
	}

	woody->Phdr[i].p_filesz += payload->len;
	woody->Phdr[i].p_memsz += payload->len;

	if (insert_payload(woody, payload, payload_position, i))
	{
		free(payload->payload);
		free(payload);
		return ft_put_error("Unable to insert payload, please regenerate it");
	}

	woody->Ehdr->e_entry = payload_position;
	woody->Phdr[i].p_flags = PF_X | PF_W | PF_R;
	free(payload->payload);
	free(payload);
	return EXIT_SUCCESS;
}

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)
	{
		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;
	return EXIT_SUCCESS;
}