[issue45842] AddressSanitizer: bad-free - hello world c extension

[Francesc Elies]

New submission from Francesc Elies :

Hi,

Context
===
we are compiling a dll with clang and it's address sanitizer and loading it via 
cffi, at random spots ASAN complains with bad-free.

  ==15100==ERROR: AddressSanitizer: attempting free on address which was 
not malloc()-ed: 0x01991a850310 in thread T0
  #0 0x7ffa1dcc7f31  
(C:\LLVM-13.0.0-win64\lib\clang\13.0.0\lib\windows\clang_rt.asan_dynamic-x86_64.dll+0x180037f31)
  #1 0x7ffa3aea59ec in _PyObject_Realloc 
D:\_w\1\s\Objects\obmalloc.c:2011
  #2 0x7ffa3af7f347 in _PyObject_GC_Resize 
D:\_w\1\s\Modules\gcmodule.c:2309
  #3 0x7ffa3aedeeaa in _PyEval_EvalCode D:\_w\1\s\Python\ceval.c:4101
  ...
  See links below for a full trace

The project where we see this it's quite complex and with many moving parts 
therefore we made a minimal reproducible example.

Reprex
==

The test boils down to the following:


win32api.LoadLibrary("LLVM-13.0.0-win64/lib/clang/13.0.0/lib/windows/clang_rt.asan_dynamic-x86_64.dll")
import hello  # hello is our compiled c extension with clang and ASAN
print(hello.system())
import pdb


If if comment the last line (import pdb) ASAN does not complain.
If instead of import pdb you import numpy the same problem can be seen.

See the following failing build 
https://github.com/FrancescElies/min_reprex_python_c_extension_asan/runs/4263693010?check_suite_focus=true
See here the CI test 
https://github.com/FrancescElies/min_reprex_python_c_extension_asan/blob/d966d3a472df71977dc6519a76be0120d2d58d39/test.py


We did not try this in linux yet, would that help?

Is this a bug? Or are we doing something wrong?

Thanks in advance for your time.

--
components: Windows
messages: 406578
nosy: FrancescElies, paul.moore, steve.dower, tim.golden, zach.ware
priority: normal
severity: normal
status: open
title: AddressSanitizer: bad-free  -  hello world c extension
versions: Python 3.10, Python 3.7, Python 3.8, Python 3.9

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[issue45842] AddressSanitizer: bad-free - hello world c extension

[Francesc Elies]

Francesc Elies  added the comment:

I tested the same script in ubuntu and got the following.

==1361==ASan runtime does not come first in initial library list; you should 
either link runtime to your application or manually preload it with LD_PRELOAD.

While on windows he does not complain about ASan runtime not bein first in 
initial library list.

Once I use LD_PRELOAD in linux. Lsan detected memory leaks, after suppressing 
them with LSAN_OPTIONS=detect_leaks=0, the script ran fine.

So far I could not find an LD_PRELOAD equivalent in windows.

I am suspecting if one would compile python with asan and run the test on 
windows, I would get similar results as in linux. Sadly at the moment asan 
suppressions doesn't seem to work on windows.

I think this is not a real bug on python but the way we are loading asan-rt in 
windows. Once I am sure I will colse this bug.

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[issue45842] AddressSanitizer: bad-free - hello world c extension

[Francesc Elies]

Francesc Elies  added the comment:

I am closing this one, bad-free is in this case a false positive.

Starting python and loading a dll which was linked with asan is incorrect.

One should asan-rt as earyly as possible, in order to do that in linux one 
should use LD_PRELOAD but in windows it's a bit more convoluted.

We made an executable which loads asan and instructed the dll DLLs to use the 
runtime linked into the main executable to avoid shadow memory collisions.

In the official docs https://clang.llvm.org/docs/AddressSanitizer.html I could 
not find much about asan with clang under windows. 

Despite the library file names where not the same as in llvm master and that 
the blogpost has msvc in mind instead of clang this blog 
https://devblogs.microsoft.com/cppblog/addresssanitizer-asan-for-windows-with-msvc/#contributions-to-asan-runtime
 pointed us in the right direction.

--
resolution:  -> not a bug
stage:  -> resolved
status: open -> closed

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