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

[Michael S. Tsirkin]

On Wed, Aug 24, 2016 at 06:41:45PM +0200, Greg Kurz wrote:
> 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).

OK, that's fine.

-- 
MST