Re: [RFC] problems with alloc_file_pseudo() use in __nfs42_ssc_open()

[Al Viro <viro@zeniv.linux.org.uk>]

On Wed, Aug 17, 2022 at 08:12:27PM -0400, Olga Kornievskaia wrote:
> On Wed, Aug 17, 2022 at 8:01 PM Al Viro <viro@zeniv.linux.org.uk> wrote:
> >
> > On Wed, Aug 17, 2022 at 06:32:15PM -0400, Olga Kornievskaia wrote:
> > > On Wed, Aug 17, 2022 at 6:18 PM Al Viro <viro@zeniv.linux.org.uk> wrote:
> > > >
> > > >         My apologies for having missed that back when the SSC
> > > > patchset had been done (and missing the problems after it got
> > > > merged, actually).
> > > >
> > > > 1) if this
> > > >         r_ino = nfs_fhget(ss_mnt->mnt_sb, src_fh, fattr);
> > > > in __nfs42_ssc_open() yields a directory inode, we are screwed
> > > > as soon as it's passed to alloc_file_pseudo() - a *lot* of places
> > > > in dcache handling would break if we do that.  It's not too
> > > > nice for a regular file from non-cooperating filesystem, but for
> > > > directory ones it's deadly.
> > >
> > > This inode is created to make an appearance of an opened file to do
> > > (an NFS) read, it's never a directory.
> >
> > Er...  Where does the fhandle come from?  From my reading it's a client-sent
> > data; I don't know what trust model do you assume, but the price of
> > getting multiple dentries over the same directory inode is high.
> > Bogus or compromised client should not be able to cause severe corruption
> > of kernel data structures...
> 
> This is an NFS spec specified operation. The (source file's)
> filehandle comes from the COPY operation compound that the destination
> server gets and then uses -- creates an inode from using the code you
> are looking at now -- to access from the source server. Security is
> all described in the spec. The uniqueness of the filehandle is
> provided by the source server that created it.

Do we assume that compromise of source server is escalatable at least
to kernel panics on the destination server anyway?  Confused...