fuzz: Ensure prevout is consensus-valid

[maflcko]

It shouldn't be possible to create consensus-invalid prevouts, so there is no need to fuzz them.

To reproduce:

$ echo 'AAAAAAEAAAAAAQF0Rw0SGsrit4+YZSEfpcQT/o+bJbjgVjATUHqrCfRE+QsBAAAXFgAUlsvXHgGV
ZxF3QXxitwe1tIOYdLj2NePHATl9CgAAAAAAGXapFOFHg1yqRFl7soeowwpIEOoe9G1NiKwCRzBE
AiAx6F2Q008gvJnok6JiyOn7lPqCJJmDiI2omRNXT1Q7XAIgCQP6WJizAqhnvImpQqYMJkqePGvx
Jy/pGRMy1iNL0ecDIQJr4tWomVTBfjpyMFMOD9aDAR5gkByOIYiaQOv8P/sRztP3pS8RDAAAEUUE
NQBwYAAAAAC5F6kUTLIzj/lKP2Hmpwyzukns2eweRkOH' | base64 --decode  > /tmp/a


$ FUZZ=script_flags ./src/test/fuzz/fuzz /tmp/a
INFO: Running with entropic power schedule (0xFF, 100).
INFO: Seed: 59714236
INFO: Loaded 1 modules   (212532 inline 8-bit counters): 212532 [0x55987fb3f668, 0x55987fb7349c), 
INFO: Loaded 1 PC tables (212532 PCs): 212532 [0x55987fb734a0,0x55987feb17e0), 
./src/test/fuzz/fuzz: Running 1 inputs 1 time(s) each.
Running: /tmp/a
fuzz: script/interpreter.cpp:1495: bool HandleMissingData(MissingDataBehavior): Assertion `!"Missing data"' failed.
==520092== ERROR: libFuzzer: deadly signal
    #0 0x55987f111180 in __sanitizer_print_stack_trace (/root/fuzz_dir/scratch/fuzz_gen/code/src/test/fuzz/fuzz+0x5ea180)
    #1 0x55987f0ba828 in fuzzer::PrintStackTrace() fuzzer.o
    #2 0x55987f09de43 in fuzzer::Fuzzer::CrashCallback() fuzzer.o
    #3 0x7fd003d563bf  (/lib/x86_64-linux-gnu/libpthread.so.0+0x153bf)
    #4 0x7fd00399a18a in raise (/lib/x86_64-linux-gnu/libc.so.6+0x4618a)
    #5 0x7fd003979858 in abort (/lib/x86_64-linux-gnu/libc.so.6+0x25858)
    #6 0x7fd003979728  (/lib/x86_64-linux-gnu/libc.so.6+0x25728)
    #7 0x7fd00398af35 in __assert_fail (/lib/x86_64-linux-gnu/libc.so.6+0x36f35)
    #8 0x55987f8ce194 in HandleMissingData(MissingDataBehavior) /root/fuzz_dir/scratch/fuzz_gen/code/src/script/interpreter.cpp:1495:9
    #9 0x55987f8ce194 in GenericTransactionSignatureChecker<CTransaction>::CheckECDSASignature(std::vector<unsigned char, std::allocator<unsigned char> > const&, std::vector<unsigned char, std::allocator<unsigned char> > const&, CScript const&, SigVersion) const /root/fuzz_dir/scratch/fuzz_gen/code/src/script/interpreter.cpp:1685:68
    #10 0x55987f8cbbc8 in EvalChecksigPreTapscript(std::vector<unsigned char, std::allocator<unsigned char> > const&, std::vector<unsigned char, std::allocator<unsigned char> > const&, prevector<28u, unsigned char, unsigned int, int>::const_iterator, prevector<28u, unsigned char, unsigned int, int>::const_iterator, unsigned int, BaseSignatureChecker const&, SigVersion, ScriptError_t*, bool&) /root/fuzz_dir/scratch/fuzz_gen/code/src/script/interpreter.cpp:363:24
    #11 0x55987f8cbbc8 in EvalChecksig(std::vector<unsigned char, std::allocator<unsigned char> > const&, std::vector<unsigned char, std::allocator<unsigned char> > const&, prevector<28u, unsigned char, unsigned int, int>::const_iterator, prevector<28u, unsigned char, unsigned int, int>::const_iterator, ScriptExecutionData&, unsigned int, BaseSignatureChecker const&, SigVersion, ScriptError_t*, bool&) /root/fuzz_dir/scratch/fuzz_gen/code/src/script/interpreter.cpp:421:16
    #12 0x55987f8c5a01 in EvalScript(std::vector<std::vector<unsigned char, std::allocator<unsigned char> >, std::allocator<std::vector<unsigned char, std::allocator<unsigned char> > > >&, CScript const&, unsigned int, BaseSignatureChecker const&, SigVersion, ScriptExecutionData&, ScriptError_t*) /root/fuzz_dir/scratch/fuzz_gen/code/src/script/interpreter.cpp:1094:26
    #13 0x55987f8d6d6e in ExecuteWitnessScript(Span<std::vector<unsigned char, std::allocator<unsigned char> > const> const&, CScript const&, unsigned int, SigVersion, BaseSignatureChecker const&, ScriptExecutionData&, ScriptError_t*) /root/fuzz_dir/scratch/fuzz_gen/code/src/script/interpreter.cpp:1843:10
    #14 0x55987f8d48fc in VerifyWitnessProgram(CScriptWitness const&, int, std::vector<unsigned char, std::allocator<unsigned char> > const&, unsigned int, BaseSignatureChecker const&, ScriptError_t*, bool) /root/fuzz_dir/scratch/fuzz_gen/code/src/script/interpreter.cpp:1904:20
    #15 0x55987f8d3d8b in VerifyScript(CScript const&, CScript const&, CScriptWitness const*, unsigned int, BaseSignatureChecker const&, ScriptError_t*) /root/fuzz_dir/scratch/fuzz_gen/code/src/script/interpreter.cpp:2045:22
    #16 0x55987f201d47 in script_flags_fuzz_target(Span<unsigned char const>) /root/fuzz_dir/scratch/fuzz_gen/code/src/test/fuzz/script_flags.cpp:54:30
    #17 0x55987f11447f in std::_Function_handler<void (Span<unsigned char const>), void (*)(Span<unsigned char const>)>::_M_invoke(std::_Any_data const&, Span<unsigned char const>&&) /usr/bin/../lib/gcc/x86_64-linux-gnu/9/../../../../include/c++/9/bits/std_function.h:300:2
    #18 0x55987f8aed17 in std::function<void (Span<unsigned char const>)>::operator()(Span<unsigned char const>) const /usr/bin/../lib/gcc/x86_64-linux-gnu/9/../../../../include/c++/9/bits/std_function.h:688:14
    #19 0x55987f8aed17 in LLVMFuzzerTestOneInput /root/fuzz_dir/scratch/fuzz_gen/code/src/test/fuzz/fuzz.cpp:63:5
    #20 0x55987f09f5e3 in fuzzer::Fuzzer::ExecuteCallback(unsigned char const*, unsigned long) fuzzer.o
    #21 0x55987f0894e2 in fuzzer::RunOneTest(fuzzer::Fuzzer*, char const*, unsigned long) fuzzer.o
    #22 0x55987f08f2da in fuzzer::FuzzerDriver(int*, char***, int (*)(unsigned char const*, unsigned long)) fuzzer.o
    #23 0x55987f0bb002 in main (/root/fuzz_dir/scratch/fuzz_gen/code/src/test/fuzz/fuzz+0x594002)
    #24 0x7fd00397b0b2 in __libc_start_main (/lib/x86_64-linux-gnu/libc.so.6+0x270b2)
    #25 0x55987f06420d in _start (/root/fuzz_dir/scratch/fuzz_gen/code/src/test/fuzz/fuzz+0x53d20d)

NOTE: libFuzzer has rudimentary signal handlers.
      Combine libFuzzer with AddressSanitizer or similar for better crash reports.
SUMMARY: libFuzzer: deadly signal

[practicalswift]

Tested ACK fa1fdeb

[adamjonas]

Fuzzed on master - immediately failed as described.
No crashes on fa1fdeb.

ACK