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Re: Curious permission problem

From: Ole Laursen
Subject: Re: Curious permission problem
Date: Wed, 17 Feb 2010 14:37:04 +0100

On Wed, Feb 17, 2010 at 1:28 PM, Michael Albinus <address@hidden> wrote:
> It's not "me" (Tramp) who causes the problem. Emacs calls `set-file-modes'
> on the original file. This fails in your case, it is not related to any
> Tramp internal temporary file.

OK, I don't really understand what's happening. I could just observe
from the strace that something inside in Emacs chmods the temporary
tramp file, i.e. a file like  /tmp/tramp.blabla, then tries to read it
which fails. I have tried to override tramp-default-file-modes to (in
my .emacs)

(defun tramp-default-file-modes (filename)
  (tramp-octal-to-decimal "0666"))

and then everything seems to work? I can open the file, save it, and
it even has the right permissions on the server side.

Just to make sure we're talking about the same thing, to reproduce,
ssh over to some server, add a file like this

  echo foo > bar
  sudo chown root bar
  sudo chmod u-rw bar
  sudo chmod g+rw bar

then try to access it with tramp. Without Tramp in Emacs 23, it fails.
With the above hack, it works.

> And yes, I believe Emacs shall follow file system conventions.
> Otherwise, it would bypass the given security level, which might result
> in undesired weaknesses.

As I see it, the problem is that you can't just map the permissions
directly from one system to another system because the users aren't
the same on the two? Actually, from a security point of view, the only
thing I care about is that nobody else on my local machine can
accidentally read the file, unless they can also read it on the remote
machine. Are there any other goals?

> PS: does the patch works for you, reading that file?

I don't have a development environment handy so I haven't figured out
how to test it yet. If you can attach the whole function, then I can
just override it from my .emacs, that would make it a bit easier?

PS: Tramp is nice. Really impressed so far.


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