| /** |
| * Copyright (C) 2020 The Android Open Source Project |
| * |
| * Licensed under the Apache License, Version 2.0 (the "License"); |
| * you may not use this file except in compliance with the License. |
| * You may obtain a copy of the License at |
| * |
| * http://www.apache.org/licenses/LICENSE-2.0 |
| * |
| * Unless required by applicable law or agreed to in writing, software |
| * distributed under the License is distributed on an "AS IS" BASIS, |
| * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. |
| * See the License for the specific language governing permissions and |
| * limitations under the License. |
| */ |
| |
| #include <dlfcn.h> |
| |
| #include "utils/String8.h" |
| |
| #define VULNERABLE_STRING "Q0bRTMaNUg" |
| |
| typedef int (*vsnprintf_t)(char *const, size_t, const char *, va_list); |
| |
| static vsnprintf_t fptr = nullptr; |
| |
| // For CVE-2020-0421 to be reproducible, the vsnprintf has to return a negative |
| // value. This negative value is added to size_t resulting in runtime error. |
| // Getting vsnprintf to return -1 is tricky. The issue produced in fuzzer was |
| // due to the call str1.appendFormat("%S", "string"). Using wide char string |
| // format specifier for regular string is not a reliable way to produce the |
| // issue. As from N1570, "If any argument is not the correct type for the |
| // corresponding conversion specification or If there are insufficient arguments |
| // for the format, the printf behavior is undefined." The below intercepting |
| // function offers a simple way to return negative value. |
| int vsnprintf(char *const dest, size_t size, const char *format, va_list ap) { |
| if (!strcmp(format, VULNERABLE_STRING)) { |
| return -1; |
| } |
| return (*fptr)(dest, size, format, ap); |
| } |
| |
| int main(void) { |
| fptr = reinterpret_cast<vsnprintf_t>(dlsym(RTLD_NEXT, "vsnprintf")); |
| if (!fptr) { |
| return EXIT_FAILURE; |
| } |
| android::String8 str1{VULNERABLE_STRING}; |
| str1.appendFormat(VULNERABLE_STRING); |
| return EXIT_SUCCESS; |
| } |