Re: Issue 62071 in oss-fuzz: elfutils:fuzz-libdwfl: Null-dereference READ in chunk_compare

[Mark Wielaard <mark@klomp.org>]

Hi Evgeny,

On Thu, 2023-09-07 at 05:31 -0700, evv… via monorail via Elfutils-devel
wrote:
> Comment #1 on issue 62071 by evv...@gmail.com: elfutils:fuzz-libdwfl: Null-dereference READ in chunk_compare
> https://bugs.chromium.org/p/oss-fuzz/issues/detail?id=62071#c1
> 
> ```
> SCARINESS: 10 (null-deref)
>     #0 0x82d35d1 in chunk_compare /src/elfutils/libelf/elf_getdata_rawchunk.c:49:25
>     #1 0xf7caab3a in __tsearch
>     #2 0x8156826 in __interceptor_tsearch /src/llvm-project/compiler-rt/lib/sanitizer_common/sanitizer_common_interceptors.inc:6057:15
>     #3 0x82d2a8a in elf_getdata_rawchunk /src/elfutils/libelf/elf_getdata_rawchunk.c:98:28
>     #4 0x81f4139 in find_elf_build_id /src/elfutils/libdwelf/dwelf_elf_gnu_build_id.c:88:28
>     #5 0x81f3a28 in __libdwfl_find_elf_build_id /src/elfutils/libdwelf/dwelf_elf_gnu_build_id.c:142:10
>     #6 0x82795e8 in __libdwfl_find_build_id /src/elfutils/libdwfl/dwfl_module_build_id.c:70:16
>     #7 0x82795e8 in dwfl_module_build_id /src/elfutils/libdwfl/dwfl_module_build_id.c:91:20
>     #8 0x81d7ec7 in dwfl_standard_find_debuginfo /src/elfutils/libdwfl/find-debuginfo.c:365:19
>     #9 0x81d3340 in find_debuginfo /src/elfutils/libdwfl/dwfl_module_getdwarf.c:538:19
>     #10 0x81cff0f in find_dw /src/elfutils/libdwfl/dwfl_module_getdwarf.c:1412:16
>     #11 0x81cff0f in dwfl_module_getdwarf /src/elfutils/libdwfl/dwfl_module_getdwarf.c:1446:3
>     #12 0x81cad03 in LLVMFuzzerTestOneInput /src/fuzz-libdwfl.c:54:3
>     #13 0x808ba2e in fuzzer::Fuzzer::ExecuteCallback(unsigned char const*, unsigned int) /src/llvm-project/compiler-rt/lib/fuzzer/FuzzerLoop.cpp:611:15
>     #14 0x808b168 in fuzzer::Fuzzer::RunOne(unsigned char const*, unsigned int, bool, fuzzer::InputInfo*, bool, bool*) /src/llvm-project/compiler-rt/lib/fuzzer/FuzzerLoop.cpp:514:3
>     #15 0x808cfdd in fuzzer::Fuzzer::ReadAndExecuteSeedCorpora(std::__Fuzzer::vector<fuzzer::SizedFile, std::__Fuzzer::allocator<fuzzer::SizedFile> >&) /src/llvm-project/compiler-rt/lib/fuzzer/FuzzerLoop.cpp:826:7
>     #16 0x808d1de in fuzzer::Fuzzer::Loop(std::__Fuzzer::vector<fuzzer::SizedFile, std::__Fuzzer::allocator<fuzzer::SizedFile> >&) /src/llvm-project/compiler-rt/lib/fuzzer/FuzzerLoop.cpp:857:3
>     #17 0x807c3fc in fuzzer::FuzzerDriver(int*, char***, int (*)(unsigned char const*, unsigned int)) /src/llvm-project/compiler-rt/lib/fuzzer/FuzzerDriver.cpp:912:6
>     #18 0x80a6177 in main /src/llvm-project/compiler-rt/lib/fuzzer/FuzzerMain.cpp:20:10
>     #19 0xf7bc5ed4 in __libc_start_main
>     #20 0x806dad5 in _start
> ```
> The fuzz target can be found at https://github.com/google/oss-fuzz/blob/master/projects/elfutils/fuzz-libdwfl.c

Thanks. But this doesn't really get me much further. Somehow a NULL key
got into the search tree and I am still unclear how that can happen.

If there is a reproducer/input file that would be really helpful.

Cheers,

Mark