secure release memory to avoid free null pointer

[abaelhe]

Build all projects

** BUILD SUCCEEDED **

bash-3.2# cd  bin/Debug/
bash-3.2# for x in ./* ; do ./$x 1> /dev/null 2>/dev/null  || echo $x ; done
./test_bind_curve_fuzzer
./test_bind_fuzzer
./test_bind_null_fuzzer
./test_connect_curve_fuzzer
./test_connect_fuzzer
./test_connect_null_fuzzer
Segmentation fault: 11
./test_security_curve
./test_z85_decode_fuzzer
bash-3.2# ./test_bind_curve_fuzzer
bash-3.2# ./test_bind_curve_fuzzer
bash-3.2# ./test_bind_fuzzer 
bash-3.2# ./test_bind_null_fuzzer 
bash-3.2# ./test_connect_curve_fuzzer 
bash-3.2# ./test_connect_fuzzer 
bash-3.2# ./test_security_curve 
Segmentation fault: 11
bash-3.2# lldb ./test_security_curve 
(lldb) target create "./test_security_curve"
Current executable set to '/Users/abaelhe/Downloads/libzmq-master/build/bin/Debug/test_security_curve' (x86_64).
(lldb) r
Process 39009 launched: '/Users/abaelhe/Downloads/libzmq-master/build/bin/Debug/test_security_curve' (x86_64)
Process 39009 stopped
* thread #3, name = 'ZMQbg/IO/0', stop reason = signal SIGSEGV
    frame #0: 0x00007ff80f64f192 libsystem_kernel.dylib`__pthread_sigmask + 10
libsystem_kernel.dylib`__pthread_sigmask:
->  0x7ff80f64f192 <+10>: jae    0x7ff80f64f19c            ; <+20>
    0x7ff80f64f194 <+12>: movq   %rax, %rdi
    0x7ff80f64f197 <+15>: jmp    0x7ff80f64a1c5            ; cerror_nocancel
    0x7ff80f64f19c <+20>: retq   
Target 0: (test_security_curve) stopped.
(lldb) bt
warning: could not find Objective-C class data in the process. This may reduce the quality of type information available.
* thread #3, name = 'ZMQbg/IO/0', stop reason = signal SIGSEGV
  * frame #0: 0x00007ff80f64f192 libsystem_kernel.dylib`__pthread_sigmask + 10
    frame #1: 0x00007ff80f685acb libsystem_pthread.dylib`pthread_sigmask + 9
    frame #2: 0x00007ff80f5d1d19 libsystem_c.dylib`abort + 112
    frame #3: 0x0000000100333551 libsodium.23.dylib`_out_of_bounds.cold.1 + 17
    frame #4: 0x0000000100316229 libsodium.23.dylib`_out_of_bounds + 9
    frame #5: 0x0000000100316218 libsodium.23.dylib`sodium_free + 408
    frame #6: 0x00000001005a6d0d libzmq.5.dylib`zmq::secure_allocator_t<unsigned char>::deallocate(this=0x00007000014c6ce0, p="", (null)=96) at secure_allocator.hpp:63:56
    frame #7: 0x00000001005a6c25 libzmq.5.dylib`std::__1::allocator_traits<zmq::secure_allocator_t<unsigned char> >::deallocate(__a=0x00007000014c6ce0, __p="", __n=96) at allocator_traits.h:282:13
    frame #8: 0x00000001005a6484 libzmq.5.dylib`std::__1::__vector_base<unsigned char, zmq::secure_allocator_t<unsigned char> >::~__vector_base(this=0x00007000014c6cd0) at vector:488:9
    frame #9: 0x00000001005acae2 libzmq.5.dylib`std::__1::vector<unsigned char, zmq::secure_allocator_t<unsigned char> >::~vector(this=0x00007000014c6cd0 size=0) at vector:579:5
    frame #10: 0x00000001005ac165 libzmq.5.dylib`std::__1::vector<unsigned char, zmq::secure_allocator_t<unsigned char> >::~vector(this=0x00007000014c6cd0 size=0) at vector:574:5
    frame #11: 0x00000001005ab2e7 libzmq.5.dylib`zmq::curve_server_t::process_hello(this=0x000000010182c600, msg_=0x00006000037001e8) at curve_server.cpp:208:1
    frame #12: 0x00000001005aad30 libzmq.5.dylib`zmq::curve_server_t::process_handshake_command(this=0x000000010182c600, msg_=0x00006000037001e8) at curve_server.cpp:104:18
    frame #13: 0x000000010062ccd7 libzmq.5.dylib`zmq::stream_engine_base_t::process_handshake_command(this=0x000000010182d400, msg_=0x00006000037001e8) at stream_engine_base.cpp:491:32
    frame #14: 0x000000010062ba21 libzmq.5.dylib`zmq::stream_engine_base_t::in_event_internal(this=0x000000010182d400) at stream_engine_base.cpp:309:14
    frame #15: 0x000000010062b665 libzmq.5.dylib`zmq::stream_engine_base_t::in_event(this=0x000000010182d400) at stream_engine_base.cpp:243:22
    frame #16: 0x00000001005c0889 libzmq.5.dylib`zmq::kqueue_t::loop(this=0x00006000037000c0) at kqueue.cpp:218:30
    frame #17: 0x00000001005eefa9 libzmq.5.dylib`zmq::worker_poller_base_t::worker_routine(arg_=0x00006000037000c0) at poller_base.cpp:146:51
    frame #18: 0x0000000100637e66 libzmq.5.dylib`thread_routine(arg_=0x0000600003700100) at thread.cpp:256:5
    frame #19: 0x00007ff80f6864e1 libsystem_pthread.dylib`_pthread_start + 125
    frame #20: 0x00007ff80f681f6b libsystem_pthread.dylib`thread_start + 15
(lldb)

[bluca]

Please add a relicense statement https://github.com/zeromq/libzmq/tree/master/RELICENSE

[abaelhe]

@bluca per your request: https://github.com/zeromq/libzmq/pull/4406

thx