Subject: Re: [PATCH 5/9] tproxy: allow non-local binds of IPv6 sockets if IP_TRANSPARENT is enabled

From: Balazs Scheidler <[email-masked]>
Date: Sat, 23 Oct 2010 16:48:14 +0200

On Fri, 2010-10-22 at 06:24 +0900, YOSHIFUJI Hideaki wrote:
> Hello.
> 
> 2010-10-20, Balazs Scheidler wrote:
> > On Wed, 2010-10-20 at 21:45 +0900, YOSHIFUJI Hideaki wrote:
> > > (2010/10/20 20:21), KOVACS Krisztian wrote:
> > > > From: Balazs Scheidler<[email-masked]>
> > > > 
> > > > Signed-off-by: Balazs Scheidler<[email-masked]>
> > > > Signed-off-by: KOVACS Krisztian<[email-masked]>
> > > > ---
> > > >   net/ipv6/af_inet6.c |    2 +-
> > > >   1 files changed, 1 insertions(+), 1 deletions(-)
> > > > 
> > > > diff --git a/net/ipv6/af_inet6.c b/net/ipv6/af_inet6.c
> > > > index 6022098..9480572 100644
> > > > --- a/net/ipv6/af_inet6.c
> > > > +++ b/net/ipv6/af_inet6.c
> > > > @@ -343,7 +343,7 @@ int inet6_bind(struct socket *sock, struct sockaddr *uaddr, int addr_len)
> > > >   			 */
> > > >   			v4addr = LOOPBACK4_IPV6;
> > > >   			if (!(addr_type&  IPV6_ADDR_MULTICAST))	{
> > > > -				if (!ipv6_chk_addr(net,&addr->sin6_addr,
> > > > +				if (!inet->transparent&&  !ipv6_chk_addr(net,&addr->sin6_addr,
> > > >   						   dev, 0)) {
> > > >   					err = -EADDRNOTAVAIL;
> > > >   					goto out_unlock;
> > > > 
> > > > 
> > > 
> > > As I wrote before in other thread, this does not seem sufficient --
> > > well, it is sufficient to allow non-local bind, but before we're
> > > allowing this, we need add checks of source address in sending side.
> > 
> > Can you please elaborate or point us to the other thread? Is it some
> > kind of address-type check that we miss?
> 
> Please see my comment at:
> <http://kerneltrap.org/mailarchive/linux-netdev/2010/7/5/6280572>
> 
> This will result in allowing non-privileged users easily sending from
> non-local / unauthorized address, which is not good, and which should
> not be allowed from security aspects.

IP_TRANSPARENT requires root (more precisely CAP_NET_ADMIN privielges)
for IPV6.

However as I see right now this check was missed from the IPv6
implementation.

Is that enough as a safeguard? e.g. something like this:

diff --git a/net/ipv6/ipv6_sockglue.c b/net/ipv6/ipv6_sockglue.c
index 0553867..f683d2c 100644
--- a/net/ipv6/ipv6_sockglue.c
+++ b/net/ipv6/ipv6_sockglue.c
@@ -343,6 +343,10 @@ static int do_ipv6_setsockopt(struct sock *sk, int level, int optname,
                break;
 
        case IPV6_TRANSPARENT:
+                if (!capable(CAP_NET_ADMIN)) {
+                        retv = -EPERM;
+                        break;
+                }
                if (optlen < sizeof(int))
                        goto e_inval;
                /* we don't have a separate transparent bit for IPV6 we use the one in the IPv4 socket */

-- 
Bazsi