1 /* 2 * Copyright (C) 2016 The Android Open Source Project 3 * 4 * Licensed under the Apache License, Version 2.0 (the "License"); 5 * you may not use this file except in compliance with the License. 6 * You may obtain a copy of the License at 7 * 8 * https://www.apache.org/licenses/LICENSE-2.0 9 * 10 * Unless required by applicable law or agreed to in writing, software 11 * distributed under the License is distributed on an "AS IS" BASIS, 12 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 13 * See the License for the specific language governing permissions and 14 * limitations under the License. 15 */ 16 17 #include <assert.h> 18 #include <limits.h> // for INT_MAX 19 #include <stdint.h> 20 #include <string.h> 21 22 #include "expat.h" 23 #include "siphash.h" 24 25 // Macros to convert preprocessor macros to string literals. See 26 // https://gcc.gnu.org/onlinedocs/gcc-3.4.3/cpp/Stringification.html 27 #define xstr(s) str(s) 28 #define str(s) #s 29 30 // The encoder type that we wish to fuzz should come from the compile-time 31 // definition `ENCODING_FOR_FUZZING`. This allows us to have a separate fuzzer 32 // binary for 33 #ifndef ENCODING_FOR_FUZZING 34 # error "ENCODING_FOR_FUZZING was not provided to this fuzz target." 35 #endif 36 37 // 16-byte deterministic hash key. 38 static unsigned char hash_key_1[16] = "FUZZING IS FUN?"; 39 static unsigned char hash_key_2[16] = "FUZZING IS FUN!"; 40 41 static void XMLCALL 42 start(void *userData, const XML_Char *name, const XML_Char **atts) { 43 (void)userData; 44 (void)name; 45 (void)atts; 46 } 47 static void XMLCALL 48 end(void *userData, const XML_Char *name) { 49 (void)userData; 50 (void)name; 51 } 52 53 static void XMLCALL 54 may_stop_character_handler(void *userData, const XML_Char *s, int len) { 55 XML_Parser parser = (XML_Parser)userData; 56 if (len > 1 && s[0] == 's') { 57 XML_StopParser(parser, s[1] == 'r' ? XML_FALSE : XML_TRUE); 58 } 59 } 60 61 static void 62 ParseOneInput(XML_Parser p, const uint8_t *data, size_t size) { 63 // Set the hash salt using siphash to generate a deterministic hash. 64 // The salt is 16 bytes and siphash24 produces 8, so the input is hashed 65 // under two keys. 66 const uint64_t first = siphash24(data, size, sip_keyof(hash_key_1)); 67 const uint64_t second = siphash24(data, size, sip_keyof(hash_key_2)); 68 uint8_t entropy[16]; 69 memcpy(entropy, &first, sizeof(first)); 70 memcpy(entropy + sizeof(first), &second, sizeof(second)); 71 XML_SetHashSalt16Bytes(p, entropy); 72 (void)sip24_valid; 73 74 XML_SetUserData(p, p); 75 XML_SetElementHandler(p, start, end); 76 XML_SetCharacterDataHandler(p, may_stop_character_handler); 77 assert(size <= INT_MAX); 78 void *buf = XML_GetBuffer(p, (int)size); 79 assert(buf); 80 memcpy(buf, data, size); 81 XML_ParseBuffer(p, (int)size, 0); 82 buf = XML_GetBuffer(p, (int)size); 83 if (buf == NULL) { 84 return; 85 } 86 memcpy(buf, data, size); 87 if (XML_ParseBuffer(p, (int)size, 1) == XML_STATUS_ERROR) { 88 XML_ErrorString(XML_GetErrorCode(p)); 89 } 90 XML_GetCurrentLineNumber(p); 91 if (size % 2) { 92 XML_ParserReset(p, NULL); 93 } 94 } 95 96 int 97 LLVMFuzzerTestOneInput(const uint8_t *data, size_t size) { 98 if (size == 0) 99 return 0; 100 101 XML_Parser parentParser = XML_ParserCreate(xstr(ENCODING_FOR_FUZZING)); 102 assert(parentParser); 103 ParseOneInput(parentParser, data, size); 104 // not freed yet, but used later and freed then 105 106 XML_Parser namespaceParser = XML_ParserCreateNS(NULL, '!'); 107 assert(namespaceParser); 108 ParseOneInput(namespaceParser, data, size); 109 XML_ParserFree(namespaceParser); 110 111 XML_Parser externalEntityParser 112 = XML_ExternalEntityParserCreate(parentParser, "e1", NULL); 113 if (externalEntityParser != NULL) { 114 ParseOneInput(externalEntityParser, data, size); 115 XML_ParserFree(externalEntityParser); 116 } 117 118 XML_Parser externalDtdParser 119 = XML_ExternalEntityParserCreate(parentParser, NULL, NULL); 120 if (externalDtdParser != NULL) { 121 ParseOneInput(externalDtdParser, data, size); 122 XML_ParserFree(externalDtdParser); 123 } 124 125 // finally frees this parser which served as parent 126 XML_ParserFree(parentParser); 127 return 0; 128 } 129