Directory permissions in chroot SFTP

[Damien Miller]

On Thu, 14 Jan 2010, Chris Adams wrote:

> Once upon a time, Damien Miller <djm at mindrot.org> said:
> > On Wed, 13 Jan 2010, Michael Masterson wrote:
> > > > Right, this is on purpose. We ban this because allowing a user write
> > > > access to a chroot target is dangerously similar to equivalence with
> > > > allowing write access to the root of a filesystem.
> > > 
> > > Could you tell me what the *real* dangers of allowing SFTP only users to write
> > > to their directories?
> > 
> > https://bugzilla.redhat.com/show_bug.cgi?id=522141
> 
> I guess I'm missing something - how does an SFTP-only user run
> something?

Server misconfiguration, bugs in sshd's unprivileged code, bugs in
sftp-server.

> Is there another way to restrict SFTP to a user's home directory?

No, and I don't think one is necessary. If having to create a
subdirectory (which users can automatically be cd'd to on sftp login) is
so onerous then feel free to reintroduce CVE-2009-2904 by removing the
checks in session.c:safely_chroot().

-d