1 //===-- FuzzerInterceptors.cpp --------------------------------------------===//
2 //
3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
4 // See https://llvm.org/LICENSE.txt for license information.
5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
6 //
7 //===----------------------------------------------------------------------===//
8 // Intercept certain libc functions to aid fuzzing.
9 // Linked only when other RTs that define their own interceptors are not linked.
10 //===----------------------------------------------------------------------===//
11
12 #include "FuzzerPlatform.h"
13
14 #if LIBFUZZER_LINUX
15
16 #define GET_CALLER_PC() __builtin_return_address(0)
17
18 #define PTR_TO_REAL(x) real_##x
19 #define REAL(x) __interception::PTR_TO_REAL(x)
20 #define FUNC_TYPE(x) x##_type
21 #define DEFINE_REAL(ret_type, func, ...) \
22 typedef ret_type (*FUNC_TYPE(func))(__VA_ARGS__); \
23 namespace __interception { \
24 FUNC_TYPE(func) PTR_TO_REAL(func); \
25 }
26
27 #include <cassert>
28 #include <cstdint>
29 #include <dlfcn.h> // for dlsym()
30 #include <sanitizer/common_interface_defs.h>
31
getFuncAddr(const char * name,uintptr_t wrapper_addr)32 static void *getFuncAddr(const char *name, uintptr_t wrapper_addr) {
33 void *addr = dlsym(RTLD_NEXT, name);
34 if (!addr) {
35 // If the lookup using RTLD_NEXT failed, the sanitizer runtime library is
36 // later in the library search order than the DSO that we are trying to
37 // intercept, which means that we cannot intercept this function. We still
38 // want the address of the real definition, though, so look it up using
39 // RTLD_DEFAULT.
40 addr = dlsym(RTLD_DEFAULT, name);
41
42 // In case `name' is not loaded, dlsym ends up finding the actual wrapper.
43 // We don't want to intercept the wrapper and have it point to itself.
44 if (reinterpret_cast<uintptr_t>(addr) == wrapper_addr)
45 addr = nullptr;
46 }
47 return addr;
48 }
49
50 static int FuzzerInited = 0;
51 static bool FuzzerInitIsRunning;
52
53 static void fuzzerInit();
54
ensureFuzzerInited()55 static void ensureFuzzerInited() {
56 assert(!FuzzerInitIsRunning);
57 if (!FuzzerInited) {
58 fuzzerInit();
59 }
60 }
61
internal_strcmp_strncmp(const char * s1,const char * s2,bool strncmp,size_t n)62 static int internal_strcmp_strncmp(const char *s1, const char *s2, bool strncmp,
63 size_t n) {
64 size_t i = 0;
65 while (true) {
66 if (strncmp) {
67 if (i == n)
68 break;
69 i++;
70 }
71 unsigned c1 = *s1;
72 unsigned c2 = *s2;
73 if (c1 != c2)
74 return (c1 < c2) ? -1 : 1;
75 if (c1 == 0)
76 break;
77 s1++;
78 s2++;
79 }
80 return 0;
81 }
82
internal_strncmp(const char * s1,const char * s2,size_t n)83 static int internal_strncmp(const char *s1, const char *s2, size_t n) {
84 return internal_strcmp_strncmp(s1, s2, true, n);
85 }
86
internal_strcmp(const char * s1,const char * s2)87 static int internal_strcmp(const char *s1, const char *s2) {
88 return internal_strcmp_strncmp(s1, s2, false, 0);
89 }
90
internal_memcmp(const void * s1,const void * s2,size_t n)91 static int internal_memcmp(const void *s1, const void *s2, size_t n) {
92 const uint8_t *t1 = static_cast<const uint8_t *>(s1);
93 const uint8_t *t2 = static_cast<const uint8_t *>(s2);
94 for (size_t i = 0; i < n; ++i, ++t1, ++t2)
95 if (*t1 != *t2)
96 return *t1 < *t2 ? -1 : 1;
97 return 0;
98 }
99
internal_strlen(const char * s)100 static size_t internal_strlen(const char *s) {
101 size_t i = 0;
102 while (s[i])
103 i++;
104 return i;
105 }
106
internal_strstr(const char * haystack,const char * needle)107 static char *internal_strstr(const char *haystack, const char *needle) {
108 // This is O(N^2), but we are not using it in hot places.
109 size_t len1 = internal_strlen(haystack);
110 size_t len2 = internal_strlen(needle);
111 if (len1 < len2)
112 return nullptr;
113 for (size_t pos = 0; pos <= len1 - len2; pos++) {
114 if (internal_memcmp(haystack + pos, needle, len2) == 0)
115 return const_cast<char *>(haystack) + pos;
116 }
117 return nullptr;
118 }
119
120 extern "C" {
121
DEFINE_REAL(int,bcmp,const void *,const void *,size_t)122 DEFINE_REAL(int, bcmp, const void *, const void *, size_t)
123 DEFINE_REAL(int, memcmp, const void *, const void *, size_t)
124 DEFINE_REAL(int, strncmp, const char *, const char *, size_t)
125 DEFINE_REAL(int, strcmp, const char *, const char *)
126 DEFINE_REAL(int, strncasecmp, const char *, const char *, size_t)
127 DEFINE_REAL(int, strcasecmp, const char *, const char *)
128 DEFINE_REAL(char *, strstr, const char *, const char *)
129 DEFINE_REAL(char *, strcasestr, const char *, const char *)
130 DEFINE_REAL(void *, memmem, const void *, size_t, const void *, size_t)
131
132 ATTRIBUTE_INTERFACE int bcmp(const char *s1, const char *s2, size_t n) {
133 if (!FuzzerInited)
134 return internal_memcmp(s1, s2, n);
135 int result = REAL(bcmp)(s1, s2, n);
136 __sanitizer_weak_hook_memcmp(GET_CALLER_PC(), s1, s2, n, result);
137 return result;
138 }
139
memcmp(const void * s1,const void * s2,size_t n)140 ATTRIBUTE_INTERFACE int memcmp(const void *s1, const void *s2, size_t n) {
141 if (!FuzzerInited)
142 return internal_memcmp(s1, s2, n);
143 int result = REAL(memcmp)(s1, s2, n);
144 __sanitizer_weak_hook_memcmp(GET_CALLER_PC(), s1, s2, n, result);
145 return result;
146 }
147
strncmp(const char * s1,const char * s2,size_t n)148 ATTRIBUTE_INTERFACE int strncmp(const char *s1, const char *s2, size_t n) {
149 if (!FuzzerInited)
150 return internal_strncmp(s1, s2, n);
151 int result = REAL(strncmp)(s1, s2, n);
152 __sanitizer_weak_hook_strncmp(GET_CALLER_PC(), s1, s2, n, result);
153 return result;
154 }
155
strcmp(const char * s1,const char * s2)156 ATTRIBUTE_INTERFACE int strcmp(const char *s1, const char *s2) {
157 if (!FuzzerInited)
158 return internal_strcmp(s1, s2);
159 int result = REAL(strcmp)(s1, s2);
160 __sanitizer_weak_hook_strcmp(GET_CALLER_PC(), s1, s2, result);
161 return result;
162 }
163
strncasecmp(const char * s1,const char * s2,size_t n)164 ATTRIBUTE_INTERFACE int strncasecmp(const char *s1, const char *s2, size_t n) {
165 ensureFuzzerInited();
166 int result = REAL(strncasecmp)(s1, s2, n);
167 __sanitizer_weak_hook_strncasecmp(GET_CALLER_PC(), s1, s2, n, result);
168 return result;
169 }
170
strcasecmp(const char * s1,const char * s2)171 ATTRIBUTE_INTERFACE int strcasecmp(const char *s1, const char *s2) {
172 ensureFuzzerInited();
173 int result = REAL(strcasecmp)(s1, s2);
174 __sanitizer_weak_hook_strcasecmp(GET_CALLER_PC(), s1, s2, result);
175 return result;
176 }
177
strstr(const char * s1,const char * s2)178 ATTRIBUTE_INTERFACE char *strstr(const char *s1, const char *s2) {
179 if (!FuzzerInited)
180 return internal_strstr(s1, s2);
181 char *result = REAL(strstr)(s1, s2);
182 __sanitizer_weak_hook_strstr(GET_CALLER_PC(), s1, s2, result);
183 return result;
184 }
185
strcasestr(const char * s1,const char * s2)186 ATTRIBUTE_INTERFACE char *strcasestr(const char *s1, const char *s2) {
187 ensureFuzzerInited();
188 char *result = REAL(strcasestr)(s1, s2);
189 __sanitizer_weak_hook_strcasestr(GET_CALLER_PC(), s1, s2, result);
190 return result;
191 }
192
193 ATTRIBUTE_INTERFACE
memmem(const void * s1,size_t len1,const void * s2,size_t len2)194 void *memmem(const void *s1, size_t len1, const void *s2, size_t len2) {
195 ensureFuzzerInited();
196 void *result = REAL(memmem)(s1, len1, s2, len2);
197 __sanitizer_weak_hook_memmem(GET_CALLER_PC(), s1, len1, s2, len2, result);
198 return result;
199 }
200
201 __attribute__((section(".preinit_array"),
202 used)) static void (*__local_fuzzer_preinit)(void) = fuzzerInit;
203
204 } // extern "C"
205
fuzzerInit()206 static void fuzzerInit() {
207 assert(!FuzzerInitIsRunning);
208 if (FuzzerInited)
209 return;
210 FuzzerInitIsRunning = true;
211
212 REAL(bcmp) = reinterpret_cast<memcmp_type>(
213 getFuncAddr("bcmp", reinterpret_cast<uintptr_t>(&bcmp)));
214 REAL(memcmp) = reinterpret_cast<memcmp_type>(
215 getFuncAddr("memcmp", reinterpret_cast<uintptr_t>(&memcmp)));
216 REAL(strncmp) = reinterpret_cast<strncmp_type>(
217 getFuncAddr("strncmp", reinterpret_cast<uintptr_t>(&strncmp)));
218 REAL(strcmp) = reinterpret_cast<strcmp_type>(
219 getFuncAddr("strcmp", reinterpret_cast<uintptr_t>(&strcmp)));
220 REAL(strncasecmp) = reinterpret_cast<strncasecmp_type>(
221 getFuncAddr("strncasecmp", reinterpret_cast<uintptr_t>(&strncasecmp)));
222 REAL(strcasecmp) = reinterpret_cast<strcasecmp_type>(
223 getFuncAddr("strcasecmp", reinterpret_cast<uintptr_t>(&strcasecmp)));
224 REAL(strstr) = reinterpret_cast<strstr_type>(
225 getFuncAddr("strstr", reinterpret_cast<uintptr_t>(&strstr)));
226 REAL(strcasestr) = reinterpret_cast<strcasestr_type>(
227 getFuncAddr("strcasestr", reinterpret_cast<uintptr_t>(&strcasestr)));
228 REAL(memmem) = reinterpret_cast<memmem_type>(
229 getFuncAddr("memmem", reinterpret_cast<uintptr_t>(&memmem)));
230
231 FuzzerInitIsRunning = false;
232 FuzzerInited = 1;
233 }
234
235 #endif
236