netdev - RE: [PATCH 4/4] net: improve the user pointer check in init_user

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Date:   Tue, 28 Jul 2020 15:52:17 +0000
From:   David Laight <David.Laight@...LAB.COM>
To:     'Jakub Kicinski' <kuba@...nel.org>, Christoph Hellwig <hch@....de>
CC:     "David S. Miller" <davem@...emloft.net>,
        Jan Engelhardt <jengelh@...i.de>,
        Ido Schimmel <idosch@...sch.org>,
        "Jason A. Donenfeld" <Jason@...c4.com>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>
Subject: RE: [PATCH 4/4] net: improve the user pointer check in
 init_user_sockptr

From: Jakub Kicinski
> Sent: 28 July 2020 16:48
> 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@...LAB.COM>
> > Signed-off-by: Christoph Hellwig <hch@....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

Not surprising - 'optlen' is a user pointer.
It should be passing 'len'.

	David

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