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 #include <string.h>
20 
21 #include "expat.h"
22 #include "siphash.h"
23 
24 // Macros to convert preprocessor macros to string literals. See
25 // https://gcc.gnu.org/onlinedocs/gcc-3.4.3/cpp/Stringification.html
26 #define xstr(s) str(s)
27 #define str(s) #s
28 
29 // The encoder type that we wish to fuzz should come from the compile-time
30 // definition `ENCODING_FOR_FUZZING`. This allows us to have a separate fuzzer
31 // binary for
32 #ifndef ENCODING_FOR_FUZZING
33 #  error "ENCODING_FOR_FUZZING was not provided to this fuzz target."
34 #endif
35 
36 // 16-byte deterministic hash key.
37 static unsigned char hash_key[16] = "FUZZING IS FUN!";
38 
39 static void XMLCALL
40 start(void *userData, const XML_Char *name, const XML_Char **atts) {
41   (void)userData;
42   (void)name;
43   (void)atts;
44 }
45 static void XMLCALL
46 end(void *userData, const XML_Char *name) {
47   (void)userData;
48   (void)name;
49 }
50 
51 static void XMLCALL
52 may_stop_character_handler(void *userData, const XML_Char *s, int len) {
53   XML_Parser parser = (XML_Parser)userData;
54   if (len > 1 && s[0] == 's') {
55     XML_StopParser(parser, s[1] == 'r' ? XML_FALSE : XML_TRUE);
56   }
57 }
58 
59 static void
60 ParseOneInput(XML_Parser p, const uint8_t *data, size_t size) {
61   // Set the hash salt using siphash to generate a deterministic hash.
62   struct sipkey *key = sip_keyof(hash_key);
63   XML_SetHashSalt(p, (unsigned long)siphash24(data, size, key));
64   (void)sip24_valid;
65 
66   XML_SetUserData(p, p);
67   XML_SetElementHandler(p, start, end);
68   XML_SetCharacterDataHandler(p, may_stop_character_handler);
69   void *buf = XML_GetBuffer(p, size);
70   assert(buf);
71   memcpy(buf, data, size);
72   XML_ParseBuffer(p, size, 0);
73   buf = XML_GetBuffer(p, size);
74   if (buf == NULL) {
75     return;
76   }
77   memcpy(buf, data, size);
78   if (XML_ParseBuffer(p, size, 1) == XML_STATUS_ERROR) {
79     XML_ErrorString(XML_GetErrorCode(p));
80   }
81   XML_GetCurrentLineNumber(p);
82   if (size % 2) {
83     XML_ParserReset(p, NULL);
84   }
85 }
86 
87 int
88 LLVMFuzzerTestOneInput(const uint8_t *data, size_t size) {
89   if (size == 0)
90     return 0;
91 
92   XML_Parser parentParser = XML_ParserCreate(xstr(ENCODING_FOR_FUZZING));
93   assert(parentParser);
94   ParseOneInput(parentParser, data, size);
95   // not freed yet, but used later and freed then
96 
97   XML_Parser namespaceParser = XML_ParserCreateNS(NULL, '!');
98   assert(namespaceParser);
99   ParseOneInput(namespaceParser, data, size);
100   XML_ParserFree(namespaceParser);
101 
102   XML_Parser externalEntityParser
103       = XML_ExternalEntityParserCreate(parentParser, "e1", NULL);
104   assert(externalEntityParser);
105   ParseOneInput(externalEntityParser, data, size);
106   XML_ParserFree(externalEntityParser);
107 
108   XML_Parser externalDtdParser
109       = XML_ExternalEntityParserCreate(parentParser, NULL, NULL);
110   assert(externalDtdParser);
111   ParseOneInput(externalDtdParser, data, size);
112   XML_ParserFree(externalDtdParser);
113 
114   // finally frees this parser which served as parent
115   XML_ParserFree(parentParser);
116   return 0;
117 }
118