Race condition in LoggerRepository access causes crashes in 0.13.0

[vanand123]

Log4cxx 0.13.0 introduced a critical thread safety change that causes applications to crash with SIGSEGV during startup when multiple threads concurrently access Logger::getLogger(). The issue is caused by commit 6505a08671b4c564f9fb5b237c856c52c126307d which replaced thread-safe LoggerRepositoryWeakPtr with unsafe raw LoggerRepository* pointers.

Environment Details:

• Log4cxx Version: 0.13.0
• Platform: Linux x86_64
• Compiler: GCC 7.5.0, C++14
• Threading: Multi-threaded application with concurrent logger access
• APR Version: 1.7.4
• APR-Util Version: 1.6.3

Problematic Commit:

• Commit Hash: 6505a08671b4c564f9fb5b237c856c52c126307d
• Title: "[LOGCXX-546] Prevent serialization of a multi-threaded application when using disabled logging statements"
• Author: Stephen Webb
• Date: January 1, 2022

Sample Code:

log4cxx::LoggerPtr testlog_control::getTestLoggerFromModuleName( const std::string &module ) const
{
    log4cxx::LoggerPtr logger = ( module==rootModuleName ? _rootLogger : log4cxx::Logger::getLogger( module ) );
    assert(logger);

    return logger;
}

Observed Crash:

#0  read () from /lib64/libc.so.6
#1  sig_handler_bt_exit at /include/bits/unistd.h:38
#2  <signal handler called>
#3  log4cxx::LogManager::getLoggerLS(std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > const&) () from /lib64/liblog4cxx.so.13
#4  log4cxx::LogManager::getLogger(std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > const&) () from /lib64/liblog4cxx.so.13
#5  log4cxx::Logger::getLogger(std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > const&) () from /lib64/liblog4cxx.so.13
#6  testlog::testlog_control::getTestLoggerFromModuleName (this=<optimized out>, module=...) at testlog_control.cpp:268
#7  testlog::testlog_control::getTestLogLevel (this=<optimized out>, module=...) at testlog_control.cpp:299
#8  testlog::testlog_control::testlog_control (this=<optimized out>, ident=<optimized out>, logfilename=<optimized out>) at testlog_control.cpp:88
#9  initTestLog (ident=<optimized out>, logfilename=<optimized out>) at testlog_control.cpp:746
#10 applstrtTaskEntry (argv=<optimized out>) at applstrt.cpp:419
#11 main (argc=<optimized out>, argv=<optimized out>) at applstrt.cpp:848

[rm5248]

Log4cxx 0.13.0 is not a supported version of Log4cxx at this point. You should upgrade to the latest released version, 1.5.0

[vanand123]

Thanks @rm5248 for quick response. I have tried building log4cxx 1.5.0 (Environment : GCC 11.5.0 with c++17 standard) but build is failing with below error

error: 'same_as' is not a member of 'std'

log4cxx 1.5.0 uses C++20 concepts (like std::same_as) in its headers.
Does this mean log4cxx 1.5.0 needs minimum c++20 standard ?
If yes, is there any log4cxx supported version which uses c++17 standard ?

[rm5248]

The minimum version is C++11. Could you post the entire error that you're getting? It's possible that there is some incorrect detection of the C++ standard.

[vanand123]

The minimum version is C++11. Could you post the entire error that you're getting? It's possible that there is some incorrect detection of the C++ standard.

@rm5248 Please find detailed error as below:

include/log4cxx/helpers/widelife.h:45:33: error: 'same_as' is not a member of 'std'
   45 |                 requires (!std::same_as<WideLife, Arg0>)
      |                                 ^~~~~~~
include/log4cxx/helpers/widelife.h:45:49: error: expected primary-expression before ',' token
   45 |                 requires (!std::same_as<WideLife, Arg0>)
      |     

Have tried below change, with this I'm not seeing above issue:

--- a/src/main/include/log4cxx/helpers/widelife.h
+++ b/src/main/include/log4cxx/helpers/widelife.h
@@ -19,7 +19,7 @@
 #define _LOG4CXX_HELPERS_WIDELIFE_H

 #include <log4cxx/log4cxx.h>
-#if defined(__cpp_concepts) && __cpp_concepts >= 201500
+#if defined(__cpp_concepts) && __cplusplus >= 202002L
 #include <concepts>
 #endif

@@ -40,7 +40,7 @@ public:
                new(&storage) T();
        }
        template <class Arg0, class... Args>
-#if defined(__cpp_concepts) && __cpp_concepts >= 201500
+#if defined(__cpp_concepts) && __cplusplus >= 202002L
                requires (!std::same_as<WideLife, Arg0>)
 #endif
        WideLife(Arg0&& arg0, Args&&... args)

But still seeing crash with same stacktrace

[rm5248]

I am unable to reproduce either of these issues on my system. It might be related to the compiler version. Would you be able to provide a minimum complete example of the issue happening?