/* This Source Code Form is subject to the terms of the Mozilla Public
* License, v. 2.0. If a copy of the MPL was not distributed with this
* file, You can obtain one at http://mozilla.org/MPL/2.0/. */
#include "mutators.h"
#include <cassert>
#include <cstring>
#include <random>
#include <tuple>
static std::tuple<uint8_t *, size_t> ParseItem(uint8_t *data,
size_t maxLength) {
// Short form. Bit 8 has value "0" and bits 7-1 give the length.
if ((data[1] & 0x80) == 0) {
size_t length = std::min(
static_cast<size_t>(data[1]), maxLength - 2);
return std::make_tuple(&data[2], length);
}
// Constructed, indefinite length. Read until {0x00, 0x00}.
if (data[1] == 0x80) {
void *offset = memmem(&data[2], maxLength - 2,
"\0", 2);
size_t length = offset ? (
static_cast<uint8_t *>(offset) - &data[2]) + 2
: maxLength - 2;
return std::make_tuple(&data[2], length);
}
// Long form. Two to 127 octets. Bit 8 of first octet has value "1"
// and bits 7-1 give the number of additional length octets.
size_t octets = std::min(
static_cast<size_t>(data[1] & 0x7f), maxLength - 2);
// Handle lengths bigger than 32 bits.
if (octets > 4) {
// Ignore any further children, assign remaining length.
return std::make_tuple(&data[2] + octets, maxLength - 2 - octets);
}
// Parse the length.
size_t length = 0;
for (size_t j = 0; j < octets; j++) {
length = (length << 8) | data[2 + j];
}
length = std::min(length, maxLength - 2 - octets);
return std::make_tuple(&data[2] + octets, length);
}
static std::vector<uint8_t *> ParseItems(uint8_t *data, size_t size) {
std::vector<uint8_t *> items;
std::vector<size_t> lengths;
// The first item is always the whole corpus.
items.push_back(data);
lengths.push_back(size);
// Can't use iterators here because the `items` vector is modified inside the
// loop. That's safe as long as we always check `items.size()` before every
// iteration, and only call `.push_back()` to append new items we found.
// Items are accessed through `items.at()`, we hold no references.
for (size_t i = 0; i < items.size(); i++) {
uint8_t *item = items.at(i);
size_t remaining = lengths.at(i);
// Empty or primitive items have no children.
if (remaining == 0 || (0x20 & item[0]) == 0) {
continue;
}
while (remaining > 2) {
uint8_t *content;
size_t length;
std::tie(content, length) = ParseItem(item, remaining);
if (length > 0) {
// Record the item.
items.push_back(content);
// Record the length for further parsing.
lengths.push_back(length);
}
// Reduce number of bytes left in current item.
remaining -= length + (content - item);
// Skip the item we just parsed.
item = content + length;
}
}
return items;
}
namespace ASN1Mutators {
size_t FlipConstructed(uint8_t *data, size_t size, size_t maxSize,
unsigned int seed) {
auto items = ParseItems(data, size);
std::mt19937 rng(seed);
std::uniform_int_distribution<size_t> dist(0, items.size() - 1);
uint8_t *item = items.at(dist(rng));
// Flip "constructed" type bit.
item[0] ^= 0x20;
return size;
}
size_t ChangeType(uint8_t *data, size_t size, size_t maxSize,
unsigned int seed) {
auto items = ParseItems(data, size);
std::mt19937 rng(seed);
std::uniform_int_distribution<size_t> dist(0, items.size() - 1);
uint8_t *item = items.at(dist(rng));
// Change type to a random int [0, 30].
static std::uniform_int_distribution<size_t> tdist(0, 30);
item[0] = tdist(rng);
return size;
}
}
// namespace ASN1Mutators
