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[libFuzzer]Add a test for defeating a hash sum.
Summary: Add a test for a data followed by 4-byte hash value. I use a slightly modified Jenkins hash function, as described in https://en.wikipedia.org/wiki/Jenkins_hash_function The modification is to ensure that hash(zeros) != 0. Reviewers: kcc Subscribers: llvm-commits Differential Revision: http://reviews.llvm.org/D12648 llvm-svn: 247076
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Ivan Krasin
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Sep 8, 2015
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// This test computes a checksum of the data (all but the last 4 bytes), | ||
// and then compares the last 4 bytes with the computed value. | ||
// A fuzzer with cmp traces is expected to defeat this check. | ||
#include <cstdint> | ||
#include <cstdlib> | ||
#include <cstring> | ||
#include <cstdio> | ||
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// A modified jenkins_one_at_a_time_hash initialized by non-zero, | ||
// so that simple_hash(0) != 0. See also | ||
// https://en.wikipedia.org/wiki/Jenkins_hash_function | ||
static uint32_t simple_hash(const uint8_t *Data, size_t Size) { | ||
uint32_t Hash = 0x12039854; | ||
for (uint32_t i = 0; i < Size; i++) { | ||
Hash += Data[i]; | ||
Hash += (Hash << 10); | ||
Hash ^= (Hash >> 6); | ||
} | ||
Hash += (Hash << 3); | ||
Hash ^= (Hash >> 11); | ||
Hash += (Hash << 15); | ||
return Hash; | ||
} | ||
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extern "C" void LLVMFuzzerTestOneInput(const uint8_t *Data, size_t Size) { | ||
if (Size < 14) | ||
return; | ||
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uint32_t Hash = simple_hash(&Data[0], Size - 4); | ||
uint32_t Want = reinterpret_cast<const uint32_t *>(&Data[Size - 4])[0]; | ||
if (Hash != Want) | ||
return; | ||
fprintf(stderr, "BINGO; simple_hash defeated: %x == %x\n", (unsigned int)Hash, | ||
(unsigned int)Want); | ||
exit(1); | ||
} |
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