Re: [Qemu-devel] [PATCH] 9pfs: disallow / in path components

[Greg Kurz]

On Wed, 24 Aug 2016 18:46:10 +0300
"Michael S. Tsirkin" <address@hidden> wrote:

> On Wed, Aug 24, 2016 at 04:00:24PM +0100, Peter Maydell wrote:
> > On 24 August 2016 at 15:29, Greg Kurz <address@hidden> wrote:  
> > > At various places in 9pfs, full paths are created by concatenating a guest
> > > originated string to the export path. A malicious guest could forge a
> > > relative path and access files outside the export path.
> > >
> > > A tentative fix was sent recently by Prasad J Pandit, but it was only
> > > focused on the local backend and did not get a positive review. This patch
> > > tries to address the issue more globally, based on the official 9P spec.
> > >
> > > The walk request described in the 9P spec [1] clearly shows that the 
> > > client
> > > is supposed to send individual path components: the official linux client
> > > never sends portions of path containing the / character for example.
> > >
> > > Moreover, the 9P spec [2] also states that a system can decide to restrict
> > > the set of supported characters used in path components, with an explicit
> > > mention "to remove slashes from name components".
> > >
> > > This patch introduces a new name_has_illegal_characters() helper that 
> > > looks
> > > for such unwanted characters in strings sent by the client. Since 9pfs is
> > > only supported on linux hosts, only the / character is checked at the
> > > moment. When support for other hosts (AKA. win32) is added, other chars
> > > may need to be blacklisted as well.  
> > 
> > Do we also need ".." and "." to be illegal names (for at least most
> > operations)?
> > 
> > thanks
> > -- PMM  
> 
> I agree, and I think this implies name_is_legal would be a better function 
> name.
> 

No I think this is a different issue that calls for a followup patch (see my
other mail).