Assertion `jmp->type == syntax_element_jump' failed

[zhangyiru]

[root@45ea9e56a3b4 boost]# ./boost_regex_fuzzer ~/boost_regex_fuzzer-testcase
INFO: Running with entropic power schedule (0xFF, 100).
INFO: Seed: 3810660610
./boost_regex_fuzzer: Running 1 inputs 1 time(s) each.
Running: /root/fusiontest-testcase-boost_regex_fuzzer-202108160002
boost_regex_fuzzer: ./boost/regex/v5/basic_regex_parser.hpp:3107: bool boost::re_detail_500::basic_regex_parser<char, boost::regex_traits>::unwind_alts(std::ptrdiff_t) [charT = char, traits = boost::regex_traits]: Assertion `jmp->type == syntax_element_jump' failed.
==22489== ERROR: libFuzzer: deadly signal
#0 0x4a70a1 in __sanitizer_print_stack_trace /src/llvm-project/compiler-rt/lib/asan/asan_stack.cpp:86:3
#1 0x6065f8 in fuzzer::PrintStackTrace() /src/llvm-project/compiler-rt/lib/fuzzer/FuzzerUtil.cpp:210:5
#2 0x5ea903 in fuzzer::Fuzzer::CrashCallback() /src/llvm-project/compiler-rt/lib/fuzzer/FuzzerLoop.cpp:233:3
#3 0x7f718324a4bf (/lib64/libpthread.so.0+0x134bf)
#4 0x7f718308f60a in raise (/lib64/libc.so.6+0x3960a)
#5 0x7f7183090930 in abort (/lib64/libc.so.6+0x3a930)
#6 0x7f7183087ec9 (/lib64/libc.so.6+0x31ec9)
#7 0x7f7183087f41 in __assert_fail (/lib64/libc.so.6+0x31f41)
#8 0x4ebfa1 in boost::re_detail_500::basic_regex_parser<char, boost::regex_traits<char, boost::cpp_regex_traits > >::unwind_alts(long) /home/boost/./boost/regex/v5/basic_regex_parser.hpp:3107:7
#9 0x4e7325 in boost::re_detail_500::basic_regex_parser<char, boost::regex_traits<char, boost::cpp_regex_traits > >::parse(char const*, char const*, unsigned int) /home/boost/./boost/regex/v5/basic_regex_parser.hpp:172:4
#10 0x4d4116 in boost::re_detail_500::basic_regex_implementation<char, boost::regex_traits<char, boost::cpp_regex_traits > >::assign(char const*, char const*, unsigned int) /home/boost/./boost/regex/v5/basic_regex.hpp:222:14
#11 0x4d3b9e in boost::basic_regex<char, boost::regex_traits<char, boost::cpp_regex_traits > >::do_assign(char const*, char const*, unsigned int) /home/boost/./boost/regex/v5/basic_regex.hpp:646:10
#12 0x4d39b8 in boost::basic_regex<char, boost::regex_traits<char, boost::cpp_regex_traits > >::assign(char const*, char const*, unsigned int) /home/boost/./boost/regex/v5/basic_regex.hpp:387:14
#13 0x4d3966 in boost::basic_regex<char, boost::regex_traits<char, boost::cpp_regex_traits > >& boost::basic_regex<char, boost::regex_traits<char, boost::cpp_regex_traits > >::assign<std::__1::char_traits, std::__1::allocator >(std::__1::basic_string<char, std::__1::char_traits, std::__1::allocator > const&, unsigned int) /home/boost/./boost/regex/v5/basic_regex.hpp:424:14
#14 0x4d1e25 in boost::basic_regex<char, boost::regex_traits<char, boost::cpp_regex_traits > >::basic_regex<std::__1::char_traits, std::__1::allocator >(std::__1::basic_string<char, std::__1::char_traits, std::__1::allocator > const&, unsigned int) /home/boost/./boost/regex/v5/basic_regex.hpp:399:7
#15 0x4d1822 in LLVMFuzzerTestOneInput /home/boost/../boost_regex_fuzzer.cc:26:18
#16 0x5ec0a3 in fuzzer::Fuzzer::ExecuteCallback(unsigned char const*, unsigned long) /src/llvm-project/compiler-rt/lib/fuzzer/FuzzerLoop.cpp:599:15
#17 0x5d7812 in fuzzer::RunOneTest(fuzzer::Fuzzer*, char const*, unsigned long) /src/llvm-project/compiler-rt/lib/fuzzer/FuzzerDriver.cpp:323:6
#18 0x5dd4de in fuzzer::FuzzerDriver(int*, char***, int ()(unsigned char const, unsigned long)) /src/llvm-project/compiler-rt/lib/fuzzer/FuzzerDriver.cpp:856:9
#19 0x606d92 in main /src/llvm-project/compiler-rt/lib/fuzzer/FuzzerMain.cpp:20:10
#20 0x7f718307bb26 in __libc_start_main (/lib64/libc.so.6+0x25b26)
#21 0x423979 in _start (/home/boost/boost_regex_fuzzer+0x423979)

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

the fuzz file and test data can get from this link
https://github.com/zhangyiru/regex_test

[zhangyiru]

pattern string：(?xi)|?+#
text string：*

thress results of regularization algorithms
（1）boost
boost-1.77 not matched（false，it should raise error because there is no valid character before "?" character）

（2）pcre2
[root@45ea9e56a3b4 try]# ./a.out "(?xi)|?+#" "*"
PCRE2 compilation failed at offset 6: quantifier does not follow a repeatable item

（3）grep -P
[root@45ea9e56a3b4 try]# grep -P "(?xi)|?+#" text
grep: nothing to repeat

pcre2 and grep -P both raise error

through analysis, it is found that lack of judgement in syntax_question in parse_extended function.
this PR determines whether the first character of the sub-expression is a question mark
#157
please review, thx~
@jzmaddock

[jzmaddock]

Confirmed the original fuzzer report, expression is "\x28\x3f\x78\x69\x29\x7c\x3f\x2b\x23\xd\x2a"

[zhangyiru]

sync to v4 version
#164