cmdline() can now throw OSError instead of AccessDenied

[amerry]

When trying to get the cmdline() of a process without sufficient permissions on Windows, since 5.5.1, it raises OSError instead of psutil.AccessDenied.

Behaviour with 5.5.0:

>>> p = psutil.Process(26944)
>>> p
psutil.Process(pid=26944, name='svchost.exe', started='10:34:01')
>>> p.cmdline()
Traceback (most recent call last):
  File "C:\Python36-32\lib\site-packages\psutil\_pswindows.py", line 712, in cmdline
    ret = cext.proc_cmdline(self.pid, use_peb=True)
PermissionError: [WinError 5] Access is denied

During handling of the above exception, another exception occurred:

PermissionError: [WinError 5] Access is denied

The above exception was the direct cause of the following exception:

Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "C:\Python36-32\lib\site-packages\psutil\__init__.py", line 768, in cmdline
    return self._proc.cmdline()
  File "C:\Python36-32\lib\site-packages\psutil\_pswindows.py", line 639, in wrapper
    return fun(self, *args, **kwargs)
  File "C:\Python36-32\lib\site-packages\psutil\_pswindows.py", line 715, in cmdline
    ret = cext.proc_cmdline(self.pid, use_peb=False)
SystemError: <class 'OSError'> returned a result with an error set

Behaviour with 5.5.1:

>>> p = psutil.Process(26944)
>>> p
psutil.Process(pid=26944, name='svchost.exe', started='10:34:01')
>>> p.cmdline()
Traceback (most recent call last):
  File "C:\Python36-32\lib\site-packages\psutil\_pswindows.py", line 635, in wrapper
    return fun(self, *args, **kwargs)
  File "C:\Python36-32\lib\site-packages\psutil\_pswindows.py", line 705, in cmdline
    ret = cext.proc_cmdline(self.pid)
PermissionError: [WinError 5] Access is denied

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "C:\Python36-32\lib\site-packages\psutil\__init__.py", line 669, in cmdline
    return self._proc.cmdline()
  File "C:\Python36-32\lib\site-packages\psutil\_pswindows.py", line 638, in wrapper
    raise AccessDenied(self.pid, self._name)
psutil._exceptions.AccessDenied: psutil.AccessDenied (pid=26944, name='svchost.exe')

This is probably a direct result of #1398

[giampaolo]

So, the difference in behavior between 5.5.0 and 5.5.1 is correct. Practically speaking it's good that you get AccessDenied and you can't do anything about that except catching AccessDenied or running the process with higher privilges.

As for the original change (#1398) I refactored that part of the code which now calls the 2 distinct methods from Python (instead of C) but it currently does not make any distinction about the Windows version against which the second method (no PEB) is tried:

psutil/psutil/_pswindows.py

Line 738 in 32c1a0d

ret = cext.proc_cmdline(self.pid, use_peb=False)

At this proposal I want to CC @EccoTheFlintstone and ask: in Python, should we avoid calling the use_peb=False method if Windows < 8.1? What happens if we do?
I know you already answered me this question but I kind of forgot. =)

[amerry]

Wait, sorry, I listed those the wrong way around. 5.5.0 has the right behaviour - throws AccessDenied - and 5.5.1 has the wrong behaviour - throws OSError.

One of my scripts broke when I upgraded, because I was throwing away AccessDenied, but that no longer works with 5.5.1.

[giampaolo]

Do you have Visual Studio installed? Could you try current GIT master version?
https://github.com/giampaolo/psutil/blob/master/INSTALL.rst#windows

[amerry]

I do! Compiling was surprisingly painless. And it looks like the problem doesn't exist on master:

>>> psutil.__version__
'5.6.0'
>>> p = psutil.Process(26944)
>>> p
psutil.Process(pid=26944, name='svchost.exe', started='10:34:01')
>>> p.cmdline()
Traceback (most recent call last):
  File "C:\dev\third-party\psutil\psutil\_pswindows.py", line 735, in cmdline
    ret = cext.proc_cmdline(self.pid, use_peb=True)
PermissionError: [WinError 5] Access is denied

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "C:\dev\third-party\psutil\psutil\_pswindows.py", line 661, in wrapper
    return fun(self, *args, **kwargs)
  File "C:\dev\third-party\psutil\psutil\_pswindows.py", line 738, in cmdline
    ret = cext.proc_cmdline(self.pid, use_peb=False)
PermissionError: [WinError 5] Access is denied

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "C:\dev\third-party\psutil\psutil\__init__.py", line 786, in cmdline
    return self._proc.cmdline()
  File "C:\dev\third-party\psutil\psutil\_pswindows.py", line 664, in wrapper
    raise AccessDenied(self.pid, self._name)
psutil.AccessDenied: psutil.AccessDenied (pid=26944, name='svchost.exe')

[giampaolo]

Beautiful. Reopening as per my question to @EccoTheFlintstone.

[EccoTheFlintstone]

At this proposal I want to CC @EccoTheFlintstone and ask: in Python, should we avoid calling the use_peb=False method if Windows < 8.1? What happens if we do?
I know you already answered me this question but I kind of forgot. =)

I think the kernel will return an error code stating that the class 60 (ProcessCommandLineInformation) you requested in NtQueryInformationProcess is not supported

I did a check on the windows version (being >= 8.1) before calling this to avoid this case (and calling NtQueryInformationProcess for nothing)

[giampaolo]

This was solved as part of #1446. Closing and releasing a new version very soon (kind of high priority).