Re: [PATCH 4/4] net: improve the user pointer check in init_user_sockptr

[Christoph Hellwig <hch@lst.de>]

On Tue, Jul 28, 2020 at 08:47:46AM -0700, Jakub Kicinski wrote:
> On Tue, 28 Jul 2020 08:36:43 +0200 Christoph Hellwig wrote:
> > Make sure not just the pointer itself but the whole range lies in
> > the user address space.  For that pass the length and then use
> > the access_ok helper to do the check.
> > 
> > Fixes: 6d04fe15f78a ("net: optimize the sockptr_t for unified kernel/user address spaces")
> > Reported-by: David Laight <David.Laight@ACULAB.COM>
> > Signed-off-by: Christoph Hellwig <hch@lst.de>
> 
> > diff --git a/net/ipv4/bpfilter/sockopt.c b/net/ipv4/bpfilter/sockopt.c
> > index 94f18d2352d007..8b132c52045973 100644
> > --- a/net/ipv4/bpfilter/sockopt.c
> > +++ b/net/ipv4/bpfilter/sockopt.c
> > @@ -65,7 +65,7 @@ int bpfilter_ip_get_sockopt(struct sock *sk, int optname,
> >  
> >  	if (get_user(len, optlen))
> >  		return -EFAULT;
> > -	err = init_user_sockptr(&optval, user_optval);
> > +	err = init_user_sockptr(&optval, user_optval, *optlen);
> >  	if (err)
> >  		return err;
> >  	return bpfilter_mbox_request(sk, optname, optval, len, false);
> 
> Appears to cause these two new warnings, sadly:
> 
> net/ipv4/bpfilter/sockopt.c:68:56: warning: dereference of noderef expression
> net/ipv4/bpfilter/sockopt.c:68:56: warning: dereference of noderef expression

Shouldn't this just be one?  That one is justified, though as *optlen
should be len.