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Re: [PATCH] ob-maxima.el: Fix execution on MS Windows

From: Max Nikulin
Subject: Re: [PATCH] ob-maxima.el: Fix execution on MS Windows
Date: Thu, 30 Dec 2021 23:33:58 +0700
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.14.0

On 30/12/2021 01:37, Nikolay Kudryavtsev wrote:
If your temporary-file-directory is something like "/tmp/apostrophe'", it would not work currently either. So apostrophe is a very special case here.

As for possible evaluation within the double quotes, while this is theoretically possible, user sort of has to go out of his way to trigger it, so the question is whether we should introduce any platform-specific code to mitigate such an obscure case? Then we are also limited by Maxima itself since it has to be able to read that path too and it's very picky when it comes to file paths.

I am not a committer, so it is up to the maintainers to decide if your patch is suitable. My intention is to draw attention to the issue, however they may tolerate it.

I have not experimented with remote execution of babel code blocks using tramp, so I may be unaware of some specific, e.g. execution using ssh almost certainly assumes shell command and interface with list of arguments may not be available.

When some external data is substituted into a Maxima command (batchload this case) there should be an extra pass of escaping that protects special characters like quotes (and backslashes?) accordingly to Maxima rules.

I expect that %S formatter does a trick by adding quotes around the string argument and adding backslashes before quote characters and backslashes inside. I suspect that quotes your added around %S must not be used there. Due to them file name appears outside of quotes at all. This error is hidden unless at least a space character presents in temporary directory path.

Unsure concerning Maxima but usually it is possible to pass arguments avoiding quoting issues for particular language. A couple of examples with inline code snippets

emacs -Q --batch --eval '(message "bl(%S)$" (car argv))' 'a"b\c.txt'
sh -c 'printf "bl(%s)\$\n" "$1"' 'sh' 'a"bc\d.txt'

Maybe there is a way to pass file name as a separate argument (without combining it with command) to Maxima as well.

In my opinion, platform-specific code should be avoided when possible. Even `shell-quote-argument' may be better. I would prefer e.g. `call-process' from info "(elisp) Synchronous Processes" https://www.gnu.org/software/emacs/manual/html_node/elisp/Synchronous-Processes.html , but I am realizing that it may require more changes in babel or even to cause problems with tramp.

Double quotes open issues with injection of commands in backticks `rm something`, $variable expansion and other constructs. I hope, `shell-quote-argument' is reliable enough.

https://xkcd.com/327/ Exploits of a Mom

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