[New-bugs-announce] [issue39584] MacOS crashes by running attached Python code

[Vinay Sharma]

New submission from Vinay Sharma <vinay0410sharma at gmail.com>:

Consider the following python Code.

```
from multiprocessing.shared_memory import SharedMemory
shm = SharedMemory(name='test-crash', create=True, size=1000000000000000000)
```

This causes macOS Catalina, Mojave to freeze and then crash. Although, this works fine on ubuntu.

After, debugging I realised that this is due to the ftruncate call. I could replicate the same by calling os.ftruncate and also using ftruncate in C code.

Following C++ code also crashes, which confirms that ftruncate in macOS is broken:

```
#include <fcntl.h>
#include <sys/shm.h>
#include <sys/stat.h>
#include <iostream>
#include <sys/mman.h>
#include <unistd.h>
#include <sys/types.h>
#include <errno.h>
#include <time.h>

int main() {

    int shm_fd = shm_open("/test-shm2", O_CREAT | O_RDWR, 0666);

    if (shm_fd == -1) {
        throw "Shared Memory Object couldn't be created or opened";
    }

    int rv = ftruncate(shm_fd, (long long)1000000000000000000);

}
```

Should python, in any way handle this, so as to prevent any crashes using python code.

----------
components: C API
messages: 361629
nosy: vinay0410
priority: normal
severity: normal
status: open
title: MacOS crashes by running attached Python code
versions: Python 3.8, Python 3.9

_______________________________________
Python tracker <report at bugs.python.org>
<https://bugs.python.org/issue39584>
_______________________________________