Re: [PATCH 7/8] conf, passt, tap: Open socket and PID files before switching UID/GID

["Richard W.M. Jones" <rjones@redhat.com>]

On Thu, Jun 20, 2024 at 02:12:53PM +0200, Stefano Brivio wrote:
> On Thu, 20 Jun 2024 12:30:54 +0100
> "Richard W.M. Jones" <rjones@redhat.com> wrote:
> 
> > On Wed, May 29, 2024 at 12:35:24PM +1000, David Gibson wrote:
> > > On Wed, May 22, 2024 at 10:59:10PM +0200, Stefano Brivio wrote:  
> > > > Otherwise, if the user runs us as root, and gives us paths that are
> > > > only accessible by root, we'll fail to open them, which might in turn
> > > > encourage users to change permissions or ownerships: definitely a bad
> > > > idea in terms of security.
> > > > 
> > > > Reported-by: Minxi Hou <mhou@redhat.com>
> > > > Reported-by: Richard W.M. Jones <rjones@redhat.com>
> > > > Signed-off-by: Stefano Brivio <sbrivio@redhat.com>  
> > > 
> > > Looking at this I did notice a pre-existing, well, maybe not bug
> > > exactly, but possibly surprising behaviour, which makes me a
> > > bit more nervous now that we can invoke it as root.
> > > 
> > > tap_sock_unix_open() will silently truncate the given socket path to
> > > the maximum length for a Unix socket.  Which means we could bind(),
> > > but also unlink() a path that's not exactly the same as the one the
> > > one the user requested.  I don't immediately see a way to exploit
> > > that, but it's the sort of thing that makes me nervous.  I think we
> > > should instead outright fail if the given socket path is too long.  
> > 
> > Yes, agreed.
> > 
> > It seems as if the latest passt code still does this.  Do you want me
> > to open a bug about it?
> 
> Yes, please, that, or a patch :)

While I was testing this, I found we do seem to check it:

https://passt.top/passt/tree/conf.c#n1446

Rich.

-- 
Richard Jones, Virtualization Group, Red Hat http://people.redhat.com/~rjones
Read my programming and virtualization blog: http://rwmj.wordpress.com
libguestfs lets you edit virtual machines.  Supports shell scripting,
bindings from many languages.  http://libguestfs.org