New submission from Chris Griffith :
It is possible to run into an IndexError in the subprocess module's
_communicate function.
```
return run(
File "subprocess.py", line 491, in run
File "subprocess.py", line 1024, in communicate
File "subprocess.py", line 1418, in _communicate
IndexError: list index out of range
```
The lines in question are:
```
if stdout is not None:
stdout = stdout[0]
if stderr is not None:
stderr = stderr[0]
```
I believe this is due to the fact there is no safety checking to make sure that
self._stdout_buff and self._stderr_buff have any content in them after being
set to empty lists.
The fix I suggest is to change the checks from `if stdout is not None` to
simply `if stdout` to make sure it is a populated list.
Example fixed code:
```
if stdout:
stdout = stdout[0]
if stderr:
stderr = stderr[0]
```
If a more stringent check is required, we could expand that out to check type
and length, such as `isinstance(stdout, list) and len(stdout) > 0:` but that is
more then necessary currently.
--
components: Library (Lib)
messages: 388211
nosy: cdgriffith
priority: normal
severity: normal
status: open
title: Subprocess IndexError possible in _communicate
type: crash
versions: Python 3.10, Python 3.8, Python 3.9
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<https://bugs.python.org/issue43423>
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