Raising an exception with %s crashes the server

[Ayuto]

Put this in an SP plugin and load the plugin. The server will crash during printing the exception.

def crash():
    name = 'asd'
    raise NameError("'%s' crash :( ... f-strings and format() work fine."% name)
    
crash()

This also happens if you replace the entire source-python/__init__.py with this snippet. Python issue? Reproduced with CS:S on Windows and Linux.

[jordanbriere]

The crash occurs when the line itself is printed to the console. The issue appears to be console_message passing the text to ConMsg which expects arguments to format the %s values. But since nothing is passed, it reads random addresses from an empty va_list when the output is formatted and forwarded to printf. This crashes:

from _core import console_message
console_message(""""'%s' crash :( ... f-strings and format() work fine."% name""")

We need to find and escape all the % to %% to tell the engine we don't want any formatting on them so that we pass the following instead:

from _core import console_message
console_message(""""'%%s' crash :( ... f-strings and format() work fine."%% name""")

EDIT: I went ahead and committed a fix for it. Running the above code now prints the expected result in the console:

sp plugin load testing
[SP] Loading plugin 'testing'...

[SP] Caught an Exception:
Traceback (most recent call last):
  File "..\addons\source-python\packages\source-python\plugins\command.py", line 162, in load_plugin
    plugin = self.manager.load(plugin_name)
  File "..\addons\source-python\packages\source-python\plugins\manager.py", line 194, in load
    plugin._load()
  File "..\addons\source-python\packages\source-python\plugins\instance.py", line 74, in _load
    self.module = import_module(self.import_name)
  File "..\addons\source-python\plugins\testing\testing.py", line 83, in <module>
    crash()
  File "..\addons\source-python\plugins\testing\testing.py", line 80, in crash
    raise NameError("'%s' crash :( ... f-strings and format() work fine."% name)

NameError: 'asd' crash :( ... f-strings and format() work fine.


[SP] Plugin 'testing' was unable to be loaded.

[Ayuto]

Hmm, I think there are better ways to fix this issue like using a function that really just prints the message instead of doing formatting stuff.

This solution can also still run into the same problem if it's getting chunked. Moreover, it doesn't take care about properly escaped percent signs.

[jordanbriere]

Hmm, I think there are better ways to fix this issue like using a function that really just prints the message instead of doing formatting stuff.

Yes, my original idea was to simply use cout or something but then we no longer have our fallback for issue #175 because we operate outside of the engine's hook. The engine doesn't provides any wrapper that doesn't use formatting. I would be fine with it, as long as it only affects listen servers but there is no guarantee that it won't also affects certain features for dedicated servers as well (for example, the OnServerOutput listener might not be able to catches these messages, etc.). Perhaps we could directly write to the CONOUT$ channel, but then it only works for dedicated servers. I believe the safest approach is to escape the formatting.

This solution can also still run into the same problem if it's getting chunked.

Good point! The replacements should be done in the loop instead.

Moreover, it doesn't take care about properly escaped percent signs.

That is not an issue. If someone pass %% to the function, then %% will be printed because %%%% is passed. Basically, the passed string is printed as is and formatting specifiers are not accepted.

[jordanbriere]

Well... the solution was actually so obvious and simple. 😆

[Ayuto]

That's a good one :D

[Ayuto]

For reference:
cf91d9c
58fa670