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//===-- FuzzerInterceptors.cpp --------------------------------------------===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//
// Intercept certain libc functions to aid fuzzing.
// Linked only when other RTs that define their own interceptors are not linked.
//===----------------------------------------------------------------------===//
#include "FuzzerPlatform.h"
#if LIBFUZZER_LINUX
#define GET_CALLER_PC() __builtin_return_address(0)
#define PTR_TO_REAL(x) real_##x
#define REAL(x) __interception::PTR_TO_REAL(x)
#define FUNC_TYPE(x) x##_type
#define DEFINE_REAL(ret_type, func, ...) \
typedef ret_type (*FUNC_TYPE(func))(__VA_ARGS__); \
namespace __interception { \
FUNC_TYPE(func) PTR_TO_REAL(func); \
}
#include <cassert>
#include <cstdint>
#include <dlfcn.h> // for dlsym()
#include <sanitizer/common_interface_defs.h>
static void *getFuncAddr(const char *name, uintptr_t wrapper_addr) {
void *addr = dlsym(RTLD_NEXT, name);
if (!addr) {
// If the lookup using RTLD_NEXT failed, the sanitizer runtime library is
// later in the library search order than the DSO that we are trying to
// intercept, which means that we cannot intercept this function. We still
// want the address of the real definition, though, so look it up using
// RTLD_DEFAULT.
addr = dlsym(RTLD_DEFAULT, name);
// In case `name' is not loaded, dlsym ends up finding the actual wrapper.
// We don't want to intercept the wrapper and have it point to itself.
if (reinterpret_cast<uintptr_t>(addr) == wrapper_addr)
addr = nullptr;
}
return addr;
}
static int FuzzerInited = 0;
static bool FuzzerInitIsRunning;
static void fuzzerInit();
static void ensureFuzzerInited() {
assert(!FuzzerInitIsRunning);
if (!FuzzerInited) {
fuzzerInit();
}
}
static int internal_strcmp_strncmp(const char *s1, const char *s2, bool strncmp,
size_t n) {
size_t i = 0;
while (true) {
if (strncmp) {
if (i == n)
break;
i++;
}
unsigned c1 = *s1;
unsigned c2 = *s2;
if (c1 != c2)
return (c1 < c2) ? -1 : 1;
if (c1 == 0)
break;
s1++;
s2++;
}
return 0;
}
static int internal_strncmp(const char *s1, const char *s2, size_t n) {
return internal_strcmp_strncmp(s1, s2, true, n);
}
static int internal_strcmp(const char *s1, const char *s2) {
return internal_strcmp_strncmp(s1, s2, false, 0);
}
static int internal_memcmp(const void *s1, const void *s2, size_t n) {
const uint8_t *t1 = static_cast<const uint8_t *>(s1);
const uint8_t *t2 = static_cast<const uint8_t *>(s2);
for (size_t i = 0; i < n; ++i, ++t1, ++t2)
if (*t1 != *t2)
return *t1 < *t2 ? -1 : 1;
return 0;
}
static size_t internal_strlen(const char *s) {
size_t i = 0;
while (s[i])
i++;
return i;
}
static char *internal_strstr(const char *haystack, const char *needle) {
// This is O(N^2), but we are not using it in hot places.
size_t len1 = internal_strlen(haystack);
size_t len2 = internal_strlen(needle);
if (len1 < len2)
return nullptr;
for (size_t pos = 0; pos <= len1 - len2; pos++) {
if (internal_memcmp(haystack + pos, needle, len2) == 0)
return const_cast<char *>(haystack) + pos;
}
return nullptr;
}
extern "C" {
DEFINE_REAL(int, bcmp, const void *, const void *, size_t)
DEFINE_REAL(int, memcmp, const void *, const void *, size_t)
DEFINE_REAL(int, strncmp, const char *, const char *, size_t)
DEFINE_REAL(int, strcmp, const char *, const char *)
DEFINE_REAL(int, strncasecmp, const char *, const char *, size_t)
DEFINE_REAL(int, strcasecmp, const char *, const char *)
DEFINE_REAL(char *, strstr, const char *, const char *)
DEFINE_REAL(char *, strcasestr, const char *, const char *)
DEFINE_REAL(void *, memmem, const void *, size_t, const void *, size_t)
ATTRIBUTE_INTERFACE int bcmp(const char *s1, const char *s2, size_t n) {
if (!FuzzerInited)
return internal_memcmp(s1, s2, n);
int result = REAL(bcmp)(s1, s2, n);
__sanitizer_weak_hook_memcmp(GET_CALLER_PC(), s1, s2, n, result);
return result;
}
ATTRIBUTE_INTERFACE int memcmp(const void *s1, const void *s2, size_t n) {
if (!FuzzerInited)
return internal_memcmp(s1, s2, n);
int result = REAL(memcmp)(s1, s2, n);
__sanitizer_weak_hook_memcmp(GET_CALLER_PC(), s1, s2, n, result);
return result;
}
ATTRIBUTE_INTERFACE int strncmp(const char *s1, const char *s2, size_t n) {
if (!FuzzerInited)
return internal_strncmp(s1, s2, n);
int result = REAL(strncmp)(s1, s2, n);
__sanitizer_weak_hook_strncmp(GET_CALLER_PC(), s1, s2, n, result);
return result;
}
ATTRIBUTE_INTERFACE int strcmp(const char *s1, const char *s2) {
if (!FuzzerInited)
return internal_strcmp(s1, s2);
int result = REAL(strcmp)(s1, s2);
__sanitizer_weak_hook_strcmp(GET_CALLER_PC(), s1, s2, result);
return result;
}
ATTRIBUTE_INTERFACE int strncasecmp(const char *s1, const char *s2, size_t n) {
ensureFuzzerInited();
int result = REAL(strncasecmp)(s1, s2, n);
__sanitizer_weak_hook_strncasecmp(GET_CALLER_PC(), s1, s2, n, result);
return result;
}
ATTRIBUTE_INTERFACE int strcasecmp(const char *s1, const char *s2) {
ensureFuzzerInited();
int result = REAL(strcasecmp)(s1, s2);
__sanitizer_weak_hook_strcasecmp(GET_CALLER_PC(), s1, s2, result);
return result;
}
ATTRIBUTE_INTERFACE char *strstr(const char *s1, const char *s2) {
if (!FuzzerInited)
return internal_strstr(s1, s2);
char *result = REAL(strstr)(s1, s2);
__sanitizer_weak_hook_strstr(GET_CALLER_PC(), s1, s2, result);
return result;
}
ATTRIBUTE_INTERFACE char *strcasestr(const char *s1, const char *s2) {
ensureFuzzerInited();
char *result = REAL(strcasestr)(s1, s2);
__sanitizer_weak_hook_strcasestr(GET_CALLER_PC(), s1, s2, result);
return result;
}
ATTRIBUTE_INTERFACE
void *memmem(const void *s1, size_t len1, const void *s2, size_t len2) {
ensureFuzzerInited();
void *result = REAL(memmem)(s1, len1, s2, len2);
__sanitizer_weak_hook_memmem(GET_CALLER_PC(), s1, len1, s2, len2, result);
return result;
}
__attribute__((section(".preinit_array"),
used)) static void (*__local_fuzzer_preinit)(void) = fuzzerInit;
} // extern "C"
static void fuzzerInit() {
assert(!FuzzerInitIsRunning);
if (FuzzerInited)
return;
FuzzerInitIsRunning = true;
REAL(bcmp) = reinterpret_cast<memcmp_type>(
getFuncAddr("bcmp", reinterpret_cast<uintptr_t>(&bcmp)));
REAL(memcmp) = reinterpret_cast<memcmp_type>(
getFuncAddr("memcmp", reinterpret_cast<uintptr_t>(&memcmp)));
REAL(strncmp) = reinterpret_cast<strncmp_type>(
getFuncAddr("strncmp", reinterpret_cast<uintptr_t>(&strncmp)));
REAL(strcmp) = reinterpret_cast<strcmp_type>(
getFuncAddr("strcmp", reinterpret_cast<uintptr_t>(&strcmp)));
REAL(strncasecmp) = reinterpret_cast<strncasecmp_type>(
getFuncAddr("strncasecmp", reinterpret_cast<uintptr_t>(&strncasecmp)));
REAL(strcasecmp) = reinterpret_cast<strcasecmp_type>(
getFuncAddr("strcasecmp", reinterpret_cast<uintptr_t>(&strcasecmp)));
REAL(strstr) = reinterpret_cast<strstr_type>(
getFuncAddr("strstr", reinterpret_cast<uintptr_t>(&strstr)));
REAL(strcasestr) = reinterpret_cast<strcasestr_type>(
getFuncAddr("strcasestr", reinterpret_cast<uintptr_t>(&strcasestr)));
REAL(memmem) = reinterpret_cast<memmem_type>(
getFuncAddr("memmem", reinterpret_cast<uintptr_t>(&memmem)));
FuzzerInitIsRunning = false;
FuzzerInited = 1;
}
#endif
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