Subject: Re: [PATCH] Fix 2.6.34-rc1 regression in disable_ipv6 support

From: Stephen Hemminger <[email-masked]>
Date: Thu, 9 Dec 2010 20:02:45 -0800

On Thu, 09 Dec 2010 10:28:10 -0500
Brian Haley <[email-masked]> wrote:

> On 12/08/2010 11:16 PM, Eric W. Biederman wrote:
> > Finding the real bug is beyond me right now, but fixing the regression
> > in disable_ipv6 is simple.  We can just delete ::1 when we bring down
> > the loopback interface, and it will be restored automatically when we
> > bring the loopback interface back up.
> 
> Hi Eric,
> 
> This would work as well, same check, different way.
> 
> Signed-off-by: Brian Haley <[email-masked]>
> 
> diff --git a/net/ipv6/addrconf.c b/net/ipv6/addrconf.c
> index 23cc8e1..5d16a9d 100644
> --- a/net/ipv6/addrconf.c
> +++ b/net/ipv6/addrconf.c
> @@ -2728,7 +2728,8 @@ static int addrconf_ifdown(struct net_device *dev, int how)
>  		   and not link-local, then retain it. */
>  		if (!how &&
>  		    (ifa->flags&IFA_F_PERMANENT) &&
> -		    !(ipv6_addr_type(&ifa->addr) & IPV6_ADDR_LINKLOCAL)) {
> +		    !(ipv6_addr_type(&ifa->addr) &
> +		      (IPV6_ADDR_LINKLOCAL|IPV6_ADDR_LOOPBACK))) {
>  			list_move_tail(&ifa->if_list, &keep_list);
>  
>  			/* If not doing DAD on this address, just keep it. */

This patch is cleaner but still fails for the non ::1 address case.

 # ip addr add 2000:db8::1/64 dev lo
 # ping6 ::1                                 -- works
 # ping6 2000:db8::1                         --works
 # ip li set dev lo down
 # ping6 ::1                                 -- does not work (expected)
 # ping6 2000:db8::1                         -- ditto
 # ip il set dev lo up
 # ping6 ::1                                 -- works (good)
 # ping6 2000:db8::1                         -- fails (network unreachable)

Looks like connected route is not getting restored correctly, probably
because loopback has NOARP flag set. 

The problem may not be true for just loopback, it may also apply to
tunnels.