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-rw-r--r--security/nss/fuzz/asn1_mutators.cc122
1 files changed, 122 insertions, 0 deletions
diff --git a/security/nss/fuzz/asn1_mutators.cc b/security/nss/fuzz/asn1_mutators.cc
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+++ b/security/nss/fuzz/asn1_mutators.cc
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+/* 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 <assert.h>
+#include <string.h>
+#include <random>
+#include <tuple>
+
+#include "asn1_mutators.h"
+
+using namespace std;
+
+static 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 = min(static_cast<size_t>(Data[1]), MaxLength - 2);
+ return 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 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 = 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 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 = min(length, MaxLength - 2 - octets);
+ return make_tuple(&Data[2] + octets, length);
+}
+
+static vector<uint8_t *> ParseItems(uint8_t *Data, size_t Size) {
+ vector<uint8_t *> items;
+ 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;
+
+ 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;
+}
+
+size_t ASN1MutatorFlipConstructed(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 ASN1MutatorChangeType(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;
+}