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  *      http://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 <stdint.h>
19 
20 #include "expat.h"
21 #include "siphash.h"
22 
23 // Macros to convert preprocessor macros to string literals. See
24 // https://gcc.gnu.org/onlinedocs/gcc-3.4.3/cpp/Stringification.html
25 #define xstr(s) str(s)
26 #define str(s) #s
27 
28 // The encoder type that we wish to fuzz should come from the compile-time
29 // definition `ENCODING_FOR_FUZZING`. This allows us to have a separate fuzzer
30 // binary for
31 #ifndef ENCODING_FOR_FUZZING
32 #  error "ENCODING_FOR_FUZZING was not provided to this fuzz target."
33 #endif
34 
35 // 16-byte deterministic hash key.
36 static unsigned char hash_key[16] = "FUZZING IS FUN!";
37 
38 static void XMLCALL
39 start(void *userData, const XML_Char *name, const XML_Char **atts) {
40   (void)userData;
41   (void)name;
42   (void)atts;
43 }
44 static void XMLCALL
45 end(void *userData, const XML_Char *name) {
46   (void)userData;
47   (void)name;
48 }
49 
50 static void XMLCALL
51 may_stop_character_handler(void *userData, const XML_Char *s, int len) {
52   XML_Parser parser = (XML_Parser)userData;
53   if (len > 1 && s[0] == 's') {
54     XML_StopParser(parser, s[1] == 'r' ? XML_FALSE : XML_TRUE);
55   }
56 }
57 
58 static void
59 ParseOneInput(XML_Parser p, const uint8_t *data, size_t size) {
60   // Set the hash salt using siphash to generate a deterministic hash.
61   struct sipkey *key = sip_keyof(hash_key);
62   XML_SetHashSalt(p, (unsigned long)siphash24(data, size, key));
63   (void)sip24_valid;
64 
65   XML_SetUserData(p, p);
66   XML_SetElementHandler(p, start, end);
67   XML_SetCharacterDataHandler(p, may_stop_character_handler);
68   XML_Parse(p, (const XML_Char *)data, size, 0);
69   if (XML_Parse(p, (const XML_Char *)data, size, 1) == XML_STATUS_ERROR) {
70     XML_ErrorString(XML_GetErrorCode(p));
71   }
72   XML_GetCurrentLineNumber(p);
73   if (size % 2) {
74     XML_ParserReset(p, NULL);
75   }
76 }
77 
78 int
79 LLVMFuzzerTestOneInput(const uint8_t *data, size_t size) {
80   XML_Parser parentParser = XML_ParserCreate(xstr(ENCODING_FOR_FUZZING));
81   assert(parentParser);
82   ParseOneInput(parentParser, data, size);
83   // not freed yet, but used later and freed then
84 
85   XML_Parser namespaceParser = XML_ParserCreateNS(NULL, '!');
86   assert(namespaceParser);
87   ParseOneInput(namespaceParser, data, size);
88   XML_ParserFree(namespaceParser);
89 
90   XML_Parser externalEntityParser
91       = XML_ExternalEntityParserCreate(parentParser, "e1", NULL);
92   assert(externalEntityParser);
93   ParseOneInput(externalEntityParser, data, size);
94   XML_ParserFree(externalEntityParser);
95 
96   XML_Parser externalDtdParser
97       = XML_ExternalEntityParserCreate(parentParser, NULL, NULL);
98   assert(externalDtdParser);
99   ParseOneInput(externalDtdParser, data, size);
100   XML_ParserFree(externalDtdParser);
101 
102   // finally frees this parser which served as parent
103   XML_ParserFree(parentParser);
104   return 0;
105 }
106