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Re: Able to write to read-only pdf files



On 14.08.21 20:19, Adriano Vilela Barbosa wrote:
On Sat, 14 Aug 2021 at 12:54, bruno zanetti <bzanetti00@gmail.com> wrote:

Il giorno sab 14 ago 2021 alle ore 15:39 Adriano Vilela Barbosa <adriano.vilela@gmail.com> ha scritto:

Hello,

Yesterday I came across a very weird behavior while annotating a pdf
file in Okular. Long story short: I opened a read-only pdf file
(permissions: 400), inserted some comments and hit the save button. At
this point, I thought I had been working on a write-enabled copy of
the file. After a while, I realized that I was actually working on the
read-only version of the file, that somehow got saved to disk when I
hit the save icon. Okular was not only able to save the file to disk,
but the file permissions were changed to 644.

I initially thought this was an Okular problem. However, after some
more testing, I was able to reproduce the problem with Xournal. This
makes me think that the problem is not with Okular or Xournal, but
with some common library used by both of these packages (maybe
libpoppler?).

Has anybody had this problem? Can anybody reproduce it?

I'm using Debian testing.

Thanks a lot,

Adriano


Hi Adriano,
the read-only permission on the pdf file just prevents it's contents to be changed. It still can be deleted if the directory it belongs to is not write protected.
Editor programs usually do not directly change the contents of a file but rather save them to a temporary new one (with default permissions), delete the original and then rename the new file replacing the original one. I don't know if Okular works this way, but I think it quite likely does.

Have a good release day!

Bruno



Hi Bruno,

Thanks for your reply.

Indeed, what you describe may be what's happening. If I change the
permissions of the directory where the file is to read-only, I get an
error message when trying to save the file. The error message says the
file could not be saved (error: access denied), and also says that it
could not write to file.pdf.part (this .part file must be temporary
file you mentioned).

I understand this mechanism, but I think this is quite controversial
and problematic. I mean, as an end user I don't care what the editor
is doing behind the scenes; it just shouldn't be able to modify a file
marked as read-only.

This is the first time I came across this behavior. No text editor I
ever used does this; LibreOffice doesn't do it either (rather, it
shows a message saying the document is open in read-only and shows an
"Edit Document" button, which allows you to edit the document and then
save it under a different name).

The question is: should I file a bug report somewhere? I really don't
want editors overwriting my read-only documents...

Thanks again,

Adriano


Adriano, I am simply a user, not a developer. I fully agree with you and suggest to file a bug report. In 30 years computing I have never noticed and assumed something like this, and although the explanation of Bruno sounds reasonable, the behavior is not reasonable at all from the point of view of a user! Until you and Bruno mentioned this behavior, I would not even have expected this to be possible by the filesystem's policy and initially reading your original post suspect this even to be a filesystem bug! If data represented by a file name is marked read-only on the filesystem level, then for this file name the data should not be replaceable. If this technically would be possible, like Bruno suspects it, then this still doesn't make it right from the users point of view.

---
Just my thoughts!
Marco.


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