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 <cstddef> // for size_t
29#include <cstdint>
30#include <dlfcn.h> // for dlsym()
31
32static void *getFuncAddr(const char *name, uintptr_t wrapper_addr) {
33 void *addr = dlsym(RTLD_NEXT, name: 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: 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
50static int FuzzerInited = 0;
51static bool FuzzerInitIsRunning;
52
53static void fuzzerInit();
54
55static void ensureFuzzerInited() {
56 assert(!FuzzerInitIsRunning);
57 if (!FuzzerInited) {
58 fuzzerInit();
59 }
60}
61
62static 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
83static int internal_strncmp(const char *s1, const char *s2, size_t n) {
84 return internal_strcmp_strncmp(s1, s2, strncmp: true, n);
85}
86
87static int internal_strcmp(const char *s1, const char *s2) {
88 return internal_strcmp_strncmp(s1, s2, strncmp: false, n: 0);
89}
90
91static 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
100static size_t internal_strlen(const char *s) {
101 size_t i = 0;
102 while (s[i])
103 i++;
104 return i;
105}
106
107static 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(s: haystack);
110 size_t len2 = internal_strlen(s: needle);
111 if (len1 < len2)
112 return nullptr;
113 for (size_t pos = 0; pos <= len1 - len2; pos++) {
114 if (internal_memcmp(s1: haystack + pos, s2: needle, n: len2) == 0)
115 return const_cast<char *>(haystack) + pos;
116 }
117 return nullptr;
118}
119
120extern "C" {
121
122// Weak hooks forward-declared to avoid dependency on
123// <sanitizer/common_interface_defs.h>.
124void __sanitizer_weak_hook_memcmp(void *called_pc, const void *s1,
125 const void *s2, size_t n, int result);
126void __sanitizer_weak_hook_strncmp(void *called_pc, const char *s1,
127 const char *s2, size_t n, int result);
128void __sanitizer_weak_hook_strncasecmp(void *called_pc, const char *s1,
129 const char *s2, size_t n, int result);
130void __sanitizer_weak_hook_strcmp(void *called_pc, const char *s1,
131 const char *s2, int result);
132void __sanitizer_weak_hook_strcasecmp(void *called_pc, const char *s1,
133 const char *s2, int result);
134void __sanitizer_weak_hook_strstr(void *called_pc, const char *s1,
135 const char *s2, char *result);
136void __sanitizer_weak_hook_strcasestr(void *called_pc, const char *s1,
137 const char *s2, char *result);
138void __sanitizer_weak_hook_memmem(void *called_pc, const void *s1, size_t len1,
139 const void *s2, size_t len2, void *result);
140
141DEFINE_REAL(int, bcmp, const void *, const void *, size_t)
142DEFINE_REAL(int, memcmp, const void *, const void *, size_t)
143DEFINE_REAL(int, strncmp, const char *, const char *, size_t)
144DEFINE_REAL(int, strcmp, const char *, const char *)
145DEFINE_REAL(int, strncasecmp, const char *, const char *, size_t)
146DEFINE_REAL(int, strcasecmp, const char *, const char *)
147DEFINE_REAL(char *, strstr, const char *, const char *)
148DEFINE_REAL(char *, strcasestr, const char *, const char *)
149DEFINE_REAL(void *, memmem, const void *, size_t, const void *, size_t)
150
151ATTRIBUTE_INTERFACE int bcmp(const char *s1, const char *s2, size_t n) {
152 if (!FuzzerInited)
153 return internal_memcmp(s1, s2, n);
154 int result = REAL(bcmp)(s1, s2, n);
155 __sanitizer_weak_hook_memcmp(GET_CALLER_PC(), s1, s2, n, result);
156 return result;
157}
158
159ATTRIBUTE_INTERFACE int memcmp(const void *s1, const void *s2, size_t n) {
160 if (!FuzzerInited)
161 return internal_memcmp(s1, s2, n);
162 int result = REAL(memcmp)(s1, s2, n);
163 __sanitizer_weak_hook_memcmp(GET_CALLER_PC(), s1, s2, n, result);
164 return result;
165}
166
167ATTRIBUTE_INTERFACE int strncmp(const char *s1, const char *s2, size_t n) {
168 if (!FuzzerInited)
169 return internal_strncmp(s1, s2, n);
170 int result = REAL(strncmp)(s1, s2, n);
171 __sanitizer_weak_hook_strncmp(GET_CALLER_PC(), s1, s2, n, result);
172 return result;
173}
174
175ATTRIBUTE_INTERFACE int strcmp(const char *s1, const char *s2) {
176 if (!FuzzerInited)
177 return internal_strcmp(s1, s2);
178 int result = REAL(strcmp)(s1, s2);
179 __sanitizer_weak_hook_strcmp(GET_CALLER_PC(), s1, s2, result);
180 return result;
181}
182
183ATTRIBUTE_INTERFACE int strncasecmp(const char *s1, const char *s2, size_t n) {
184 ensureFuzzerInited();
185 int result = REAL(strncasecmp)(s1, s2, n);
186 __sanitizer_weak_hook_strncasecmp(GET_CALLER_PC(), s1, s2, n, result);
187 return result;
188}
189
190ATTRIBUTE_INTERFACE int strcasecmp(const char *s1, const char *s2) {
191 ensureFuzzerInited();
192 int result = REAL(strcasecmp)(s1, s2);
193 __sanitizer_weak_hook_strcasecmp(GET_CALLER_PC(), s1, s2, result);
194 return result;
195}
196
197ATTRIBUTE_INTERFACE char *strstr(const char *s1, const char *s2) {
198 if (!FuzzerInited)
199 return internal_strstr(haystack: s1, needle: s2);
200 char *result = REAL(strstr)(s1, s2);
201 __sanitizer_weak_hook_strstr(GET_CALLER_PC(), s1, s2, result);
202 return result;
203}
204
205ATTRIBUTE_INTERFACE char *strcasestr(const char *s1, const char *s2) {
206 ensureFuzzerInited();
207 char *result = REAL(strcasestr)(s1, s2);
208 __sanitizer_weak_hook_strcasestr(GET_CALLER_PC(), s1, s2, result);
209 return result;
210}
211
212ATTRIBUTE_INTERFACE
213void *memmem(const void *s1, size_t len1, const void *s2, size_t len2) {
214 ensureFuzzerInited();
215 void *result = REAL(memmem)(s1, len1, s2, len2);
216 __sanitizer_weak_hook_memmem(GET_CALLER_PC(), s1, len1, s2, len2, result);
217 return result;
218}
219
220__attribute__((section(".preinit_array"),
221 used)) static void (*__local_fuzzer_preinit)(void) = fuzzerInit;
222
223} // extern "C"
224
225static void fuzzerInit() {
226 assert(!FuzzerInitIsRunning);
227 if (FuzzerInited)
228 return;
229 FuzzerInitIsRunning = true;
230
231 REAL(bcmp) = reinterpret_cast<memcmp_type>(
232 getFuncAddr(name: "bcmp", wrapper_addr: reinterpret_cast<uintptr_t>(&bcmp)));
233 REAL(memcmp) = reinterpret_cast<memcmp_type>(
234 getFuncAddr(name: "memcmp", wrapper_addr: reinterpret_cast<uintptr_t>(&memcmp)));
235 REAL(strncmp) = reinterpret_cast<strncmp_type>(
236 getFuncAddr(name: "strncmp", wrapper_addr: reinterpret_cast<uintptr_t>(&strncmp)));
237 REAL(strcmp) = reinterpret_cast<strcmp_type>(
238 getFuncAddr(name: "strcmp", wrapper_addr: reinterpret_cast<uintptr_t>(&strcmp)));
239 REAL(strncasecmp) = reinterpret_cast<strncasecmp_type>(
240 getFuncAddr(name: "strncasecmp", wrapper_addr: reinterpret_cast<uintptr_t>(&strncasecmp)));
241 REAL(strcasecmp) = reinterpret_cast<strcasecmp_type>(
242 getFuncAddr(name: "strcasecmp", wrapper_addr: reinterpret_cast<uintptr_t>(&strcasecmp)));
243 REAL(strstr) = reinterpret_cast<strstr_type>(
244 getFuncAddr(name: "strstr", wrapper_addr: reinterpret_cast<uintptr_t>(&strstr)));
245 REAL(strcasestr) = reinterpret_cast<strcasestr_type>(
246 getFuncAddr(name: "strcasestr", wrapper_addr: reinterpret_cast<uintptr_t>(&strcasestr)));
247 REAL(memmem) = reinterpret_cast<memmem_type>(
248 getFuncAddr(name: "memmem", wrapper_addr: reinterpret_cast<uintptr_t>(&memmem)));
249
250 FuzzerInitIsRunning = false;
251 FuzzerInited = 1;
252}
253
254#endif
255