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bug#28811:; preview-at-point

From: Ken Sharp
Subject: bug#28811:; preview-at-point
Date: Sat, 04 Nov 2017 19:27:39 +0000

At 18:16 04/11/2017 +0100, David Kastrup wrote:

> Well the obvious suggestion is simply 'don't use SAFER and DELAYSAFER'
> because then you don't need .runandhide :-)

They are there for a reason, aren't they?

Yes, though I would (and have) argued against them. The interpreter is intended to be able to access the file system (as permitted by the language specification). Nevertheless, the capability exists to prevent that, because people asked for it.

It's rendering individual PostScript files in an order determined by the
current position in a viewer (in this case an Emacs file), and the
individual files are externally provided, so they may contain malicious

Provided they are in the current directory, as far as I'm aware you don't need to break SAFER for them, because the Current worming directory is permitted. I can't recall if that requires -P- or not, it may do.

Pretty much the principal reason for the existence of DELAYSAFER.

DELAYSAFER is there to permit operations to be concluded that won't work if you have SAFER. This is, however, a massive security hole, there are nay number of implementations and 'recipes' out there which use SAFER and DELAYSAFER and never call .setsafe. Also WRITESYSTEMDICT and other things.

In any event, DELAYSAFER hasn't changed.

This uses Ghostscript interactively via pipes (or a tty, I forget
which): if there was a mode "be unsafe on the Ghostscript interpreter
command line and safe within files read from there", that would work.

No way that Ghostscript can tell the difference, at the interpreter level, it all just comes in as streamed data.

How are safe PostScript viewers to be implemented now?

Well, you can use SAFER, you can even use DELAYSAFER, that has not changed. What I'm questioning is the use of .runandhide.


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