Python: Add query for unsafe use of tempfile.mktemp.

[taus-semmle]

Title says it all.

@felicity-semmle for the change note and qhelp.

[felicitymay]

Thanks for pinging me. I've made a few text suggestions, but nothing major.

[felicitymay]

The convention is to put code elements in single quotes in the description, so mktemp -> 'mktemp'.

[taus-semmle]

I've rewritten the description, since the query now supports two other insecure functions (but perhaps it's too vague now?). Please let me know if you think it needs further changes.

[felicitymay]

Suggest revising along the following lines to reduce sentence length and, I hope, improve clarity:

Using the mktemp function in the tempfile module to create a file is insecure because the function doesn't ensure exclusive access to the file. It returns a filename that is guaranteed to be unique on creation but the file must be opened in a separate operation. There is no guarantee that the creation and open operations will happen atomically. This provides an opportunity for an attacker to interfere with the file before it is opened.

[taus-semmle]

I have rewritten this based on your suggestions.

[felicitymay]

Thanks for the changes. One small suggestion over the description, but otherwise the text seems fine (although it would be nice to see a preview of the qhelp once the conflicts are resolved).

[felicitymay]

Presumably there are some ways to create a temporary file securely, so perhaps: "Creating a temporary file using this method may be insecure."?

[taus-semmle]

Done.

[markshannon]

Code and tests look fine now.