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Re: CVE# request: pigz creates temp file with insecure permissions
From: Michael Tokarev <mjt () tls msk ru>
Date: Sat, 16 Feb 2013 09:59:07 +0400

15.02.2013 23:33, Kurt Seifried wrote:
On 02/15/2013 06:43 AM, Matthias Weckbecker wrote:
On Friday 15 February 2013 09:33:30 Michael Tokarev wrote:
I think this one well deserves a CVE#.  I just submitted the
following bug #700608 to Debian BTS:

Not sure if this qualifies for a CVE. At least similar issues did
not get one in the past.


From the last discussion of this:

http://www.openwall.com/lists/oss-security/2012/09/24/4
http://www.openwall.com/lists/oss-security/2012/09/24/8
http://www.openwall.com/lists/oss-security/2012/09/24/9
http://www.openwall.com/lists/oss-security/2012/09/26/6

Basically I pointed out we need to define what information
MUST/SHOULD/SHOULD NOT/MUST NOT be marked as sensitive/etc so we can
apply appropriate file permissions and the discussion died.

So no CVE for this. Set your umask to be safe for now (and probably
forever =).

This is definitely wrong.  In my opinion, anyway.

I remember well the gnupg discussion.  That one is really questionable.
Especially when it creates an encrypted file from non-encrypted but
protected data - the result is not necessary to be protected with
file permissions since it is encrypted.

Gnupg deals with security data explicitly.  When you encrypt/decrypt
data using it, you expect to be aware of when you cross encryption
boundaries and deal with the consequences using umask.  But even
there, I expect to have all temp files with strong permissions, so
I don't have to deal with these _too_.

Here, the utility is not crossing any encryption boundaries like gnupg
does, and its aim (and end result) is to _preserve_ attributes (incl.
permission bits).  What it have in-process - to end-user anywa - looks
like an internal temp file (that's why I used this word in the subject).
Ie, the result is correct (the permission bits), but a temp file is
insecure.  I just don't expect to have a widely open temp file which
reveals my secrets!

pigz here does not differ from, say, cp utility - when I ask it to copy
foo to bar, I expect it to keep bar at least as private as foo is, --
the result AND the temp file during copy.  If cp(1) behaved this way,
creating destination file with 0666&umask and chmod'ing it when the
copy is done, that'd be insane.

Suggesting to have "safe" umask is entirely unpractical in this context.
I do have safe umask which lets me to do my work and share it with others.
Making it to drop permissions for !me means lots of headaches in other
places, much more than necessary or tolerable.  And thinking and especially
choosing which umask to use for EVERY process is, again, completely
unpractical.

I just expect a tool to not reveal information more than it already is,
and, well, to implement common sence.  This, and other examples of cp,
gzip, etc, always creating temp files with restricted permission -- all
are good examples of common sence, where pigz does not follow the
natural expected practice.  And it _hides_ that fact by creating only
the "temp" file insecurely, -- the result is secured properly and looking
there, users are unusupected that they private data has been already read.

Thanks,

/mjt


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