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