[Python-Dev] [Python-checkins] cpython (2.7): Fix closes issue10761: tarfile.extractall failure when symlinked files are

[Antoine Pitrou]

On Thu, 28 Apr 2011 22:44:50 +0800
Senthil Kumaran <orsenthil at gmail.com> wrote:
> On Thu, Apr 28, 2011 at 04:20:06PM +0200, Éric Araujo wrote:
> > >          if hasattr(os, "symlink") and hasattr(os, "link"):
> > >              # For systems that support symbolic and hard links.
> > >              if tarinfo.issym():
> > > +                if os.path.exists(targetpath):
> > > +                    os.unlink(targetpath)
> > 
> > Is there a race condition here?
> 
> The lock to avoid race conditions (if you were thinking along those
> lines) would usually be implemented at the higher level code which is
> using extractall in threads.

A lock would only protect only against multi-threaded use of the
tarfile module, which is probably quite rare and therefore not a real
concern.
The kind of race condition which can happen here is if an attacker
creates "targetpath" between os.path.exists and os.unlink. Whether it
is an exploitable flaw would need a detailed analysis, of course.

Regards

Antoine.