Memsan reports use-of-uninitialized-value in 1.76.0 temp_directory_path()

[tonyelewis]

Compiling and executing the following code with Boost 1.75, Clang 10.0 and -fsanitize=memory -fsanitize-memory-track-origins -fno-omit-frame-pointer:

#include <boost/filesystem.hpp>

int main() {
	::boost::filesystem::temp_directory_path();
}

…gives:

==8==WARNING: MemorySanitizer: use-of-uninitialized-value
    #0 0x4d1fd6 in boost::filesystem::detail::status(boost::filesystem::path const&, boost::system::error_code*) /root/.conan/data/boost/1.75.0/_/_/source/source_subfolder/libs/filesystem/src/operations.cpp:2603:7
    #1 0x4ed91a in boost::filesystem::detail::temp_directory_path(boost::system::error_code*) /root/.conan/data/boost/1.75.0/_/_/source/source_subfolder/libs/filesystem/src/operations.cpp:2799:24
    #2 0x49fe1c in boost::filesystem::temp_directory_path() (/fsprob/build/fsprob+0x49fe1c)
    #3 0x49a9f8 in main (/fsprob/build/fsprob+0x49a9f8)
    #4 0x7f46792830b2 in __libc_start_main (/lib/x86_64-linux-gnu/libc.so.6+0x270b2)
    #5 0x41f8bd in _start (/fsprob/build/fsprob+0x41f8bd)

  Uninitialized value was created by an allocation of 'path_stat' in the stack frame of function '_ZN5boost10filesystem6detail6statusERKNS0_4pathEPNS_6system10error_codeE'
    #0 0x4d0d90 in boost::filesystem::detail::status(boost::filesystem::path const&, boost::system::error_code*) /root/.conan/data/boost/1.75.0/_/_/source/source_subfolder/libs/filesystem/src/operations.cpp:2572

SUMMARY: MemorySanitizer: use-of-uninitialized-value /root/.conan/data/boost/1.75.0/_/_/source/source_subfolder/libs/filesystem/src/operations.cpp:2603:7 in boost::filesystem::detail::status(boost::filesystem::path const&, boost::system::error_code*)
Exiting

[tonyelewis]

Files to repro (with spurious .txt extensions in some cases for attaching to GitHub):

• fsprob.cpp.txt
• Dockerfile.txt
• conanfile.txt
• CMakeLists.txt

The errors with the original colouring codes:

• errors.with-colouring.txt

[tonyelewis]

Note: in this case I'm not using a standard library built with the memory sanitiser enabled, but:

1. the error stacktrace isn't going through the standard library
2. I've seen the same error in another configuration that does use a standard library built with the memory sanitiser enabled

[tonyelewis]

Ah - I see that there's a new Conan recipe for Boost 1.76.0. I've retested with 1.76.0 and the problem persists. I'll update the title of the issue to reflect that.

Here is an updated conanfile.txt.

[Lastique]

This is a false positive. The backtrace points to the check for path_stat.stx_mask, which must be set by the statx syscall.

[tonyelewis]

Thank you for your response. If there are are OS calls that can't be instrumented, can we annotate that in the Boost Filesystem code, so that users don't get lots of false positives when they try to memory-sanitize their code that uses the library?

I tried creating a macro that expands to the appropriate attribute when compiling with the memory sanitizer enabled:

#ifdef __has_feature
#  if __has_feature(memory_sanitizer)
#    define BOOST_NO_SANITIZE_MEMORY __attribute__((no_sanitize("memory")))
#  else
#    define BOOST_NO_SANITIZE_MEMORY
#  endif
#else
#  define BOOST_NO_SANITIZE_MEMORY
#endif

…and for my example, I put the following before the definition of file_status status(const path &, error_code*):

#if defined(BOOST_FILESYSTEM_HAS_STATX) || defined(BOOST_FILESYSTEM_HAS_STATX_SYSCALL)
  BOOST_NO_SANITIZE_MEMORY
#endif

…and that allowed my motivating example to run without complaint.

Given that there seem to be quite a few calls to statx(), maybe it'd make sense to have an inline function decorated with BOOST_NO_SANITIZE_MEMORY that just forwards to statx()?

---

For reference, I tested this by getting the Dockerfile to build the Boost via Conan, and then doing an extra copy of the locally modified fs source file and forced rebuild:

COPY operations.cpp /root/.conan/data/boost/1.76.0/_/_/source/source_subfolder/libs/filesystem/src
RUN conan install --build -s build_type=Debug --install-folder /fsprob/build /fsprob