Re: [Patch net] ipv6: ignore null_entry in inet6_rtm_getroute() too

[Cong Wang]

On Tue, Feb 28, 2017 at 2:35 PM, David Ahern  wrote:
> On 2/28/17 11:48 AM, Cong Wang wrote:
>> On Tue, Feb 28, 2017 at 11:01 AM, David Ahern  
>> wrote:
>>> On 2/28/17 10:44 AM, Cong Wang wrote:
 Like commit 1f17e2f2c8a8 ("net: ipv6: ignore null_entry on route dumps"),
 we need to ignore null entry in inet6_rtm_getroute() too.

 Return -ENOENT here because we return the same errno when deleting
 the null entry.

 Fixes: a1a22c1206 ("net: ipv6: Keep nexthop of multipath route on admin 
 down")
 Reported-by: Dmitry Vyukov 
 Cc: David Ahern 
 Signed-off-by: Cong Wang 
 ---
  net/ipv6/route.c | 6 ++
  1 file changed, 6 insertions(+)

 diff --git a/net/ipv6/route.c b/net/ipv6/route.c
 index f54f426..25590d1 100644
 --- a/net/ipv6/route.c
 +++ b/net/ipv6/route.c
 @@ -3627,6 +3627,12 @@ static int inet6_rtm_getroute(struct sk_buff 
 *in_skb, struct nlmsghdr *nlh)
   rt = (struct rt6_info *)ip6_route_output(net, NULL, );
   }

 + if (rt == net->ipv6.ip6_null_entry) {
 + ip6_rt_put(rt);
 + err = -ENOENT;
 + goto errout;
 + }
 +
   skb = alloc_skb(NLMSG_GOODSIZE, GFP_KERNEL);
   if (!skb) {
   ip6_rt_put(rt);

>>>
>>> hold on. That test exposed something else, not just a getroute problem.
>>> I accidentally ran 'unsahre -n; ip -6 ro ls' on my host machine instead
>>> of a VM, so took some time to recover. dumproute already covers the null
>>> route.
>
> My host was running a slightly older kernel (did not have the null_entry
> check in the dump route path for one).
>
> As for trapping null_entry on getroute, this changes user experience.
> Right now you always get a route response for IPv6 with the error set as
> rta_error. This patch changes that. I am fine with it since it makes
> IPv6 more like IPv4:
>
> # ip -6 ro get 2001:db8:12::1
> RTNETLINK answers: Network is unreachable
>

Yeah, I am not sure if we really want to "return" the null entry here,
since we ignore it in dump anyway. If we really want, an alternative
patch is probably something like:

diff --git a/net/ipv6/route.c b/net/ipv6/route.c
index 25590d1..e60dc1c 100644
--- a/net/ipv6/route.c
+++ b/net/ipv6/route.c
@@ -3322,7 +3322,7 @@ static int rt6_nexthop_info(struct sk_buff *skb,
struct rt6_info *rt,
 {
if (!netif_running(rt->dst.dev) || !netif_carrier_ok(rt->dst.dev)) {
*flags |= RTNH_F_LINKDOWN;
-   if (rt->rt6i_idev->cnf.ignore_routes_with_linkdown)
+   if (rt->rt6i_idev &&
rt->rt6i_idev->cnf.ignore_routes_with_linkdown)
*flags |= RTNH_F_DEAD;
}


> But, if we are going to do this then err should be set based on
> rt->dst.error (ENOENT is not the right error) and the commit message
> should state the change.
>

Makes sense, I will change the errno and update changelog.

Re: [Patch net] ipv6: ignore null_entry in inet6_rtm_getroute() too

[David Ahern]

On 2/28/17 11:48 AM, Cong Wang wrote:
> On Tue, Feb 28, 2017 at 11:01 AM, David Ahern  
> wrote:
>> On 2/28/17 10:44 AM, Cong Wang wrote:
>>> Like commit 1f17e2f2c8a8 ("net: ipv6: ignore null_entry on route dumps"),
>>> we need to ignore null entry in inet6_rtm_getroute() too.
>>>
>>> Return -ENOENT here because we return the same errno when deleting
>>> the null entry.
>>>
>>> Fixes: a1a22c1206 ("net: ipv6: Keep nexthop of multipath route on admin 
>>> down")
>>> Reported-by: Dmitry Vyukov 
>>> Cc: David Ahern 
>>> Signed-off-by: Cong Wang 
>>> ---
>>>  net/ipv6/route.c | 6 ++
>>>  1 file changed, 6 insertions(+)
>>>
>>> diff --git a/net/ipv6/route.c b/net/ipv6/route.c
>>> index f54f426..25590d1 100644
>>> --- a/net/ipv6/route.c
>>> +++ b/net/ipv6/route.c
>>> @@ -3627,6 +3627,12 @@ static int inet6_rtm_getroute(struct sk_buff 
>>> *in_skb, struct nlmsghdr *nlh)
>>>   rt = (struct rt6_info *)ip6_route_output(net, NULL, );
>>>   }
>>>
>>> + if (rt == net->ipv6.ip6_null_entry) {
>>> + ip6_rt_put(rt);
>>> + err = -ENOENT;
>>> + goto errout;
>>> + }
>>> +
>>>   skb = alloc_skb(NLMSG_GOODSIZE, GFP_KERNEL);
>>>   if (!skb) {
>>>   ip6_rt_put(rt);
>>>
>>
>> hold on. That test exposed something else, not just a getroute problem.
>> I accidentally ran 'unsahre -n; ip -6 ro ls' on my host machine instead
>> of a VM, so took some time to recover. dumproute already covers the null
>> route.

My host was running a slightly older kernel (did not have the null_entry
check in the dump route path for one).

As for trapping null_entry on getroute, this changes user experience.
Right now you always get a route response for IPv6 with the error set as
rta_error. This patch changes that. I am fine with it since it makes
IPv6 more like IPv4:

# ip -6 ro get 2001:db8:12::1
RTNETLINK answers: Network is unreachable

But, if we are going to do this then err should be set based on
rt->dst.error (ENOENT is not the right error) and the commit message
should state the change.

Re: [Patch net] ipv6: ignore null_entry in inet6_rtm_getroute() too

[Cong Wang]

On Tue, Feb 28, 2017 at 11:01 AM, David Ahern  wrote:
> On 2/28/17 10:44 AM, Cong Wang wrote:
>> Like commit 1f17e2f2c8a8 ("net: ipv6: ignore null_entry on route dumps"),
>> we need to ignore null entry in inet6_rtm_getroute() too.
>>
>> Return -ENOENT here because we return the same errno when deleting
>> the null entry.
>>
>> Fixes: a1a22c1206 ("net: ipv6: Keep nexthop of multipath route on admin 
>> down")
>> Reported-by: Dmitry Vyukov 
>> Cc: David Ahern 
>> Signed-off-by: Cong Wang 
>> ---
>>  net/ipv6/route.c | 6 ++
>>  1 file changed, 6 insertions(+)
>>
>> diff --git a/net/ipv6/route.c b/net/ipv6/route.c
>> index f54f426..25590d1 100644
>> --- a/net/ipv6/route.c
>> +++ b/net/ipv6/route.c
>> @@ -3627,6 +3627,12 @@ static int inet6_rtm_getroute(struct sk_buff *in_skb, 
>> struct nlmsghdr *nlh)
>>   rt = (struct rt6_info *)ip6_route_output(net, NULL, );
>>   }
>>
>> + if (rt == net->ipv6.ip6_null_entry) {
>> + ip6_rt_put(rt);
>> + err = -ENOENT;
>> + goto errout;
>> + }
>> +
>>   skb = alloc_skb(NLMSG_GOODSIZE, GFP_KERNEL);
>>   if (!skb) {
>>   ip6_rt_put(rt);
>>
>
> hold on. That test exposed something else, not just a getroute problem.
> I accidentally ran 'unsahre -n; ip -6 ro ls' on my host machine instead
> of a VM, so took some time to recover. dumproute already covers the null
> route.
>

Of course, you already stated it in your commit:

ip6_null_entry is the root of all ipv6 fib tables making it integrated
into the table and hence passed to the ipv6 route dump code. The
null_entry route uses the loopback device for dst.dev but may not have
rt6i_idev set because of the order in which initializations are done --
ip6_route_net_init is run before addrconf_init has initialized the
loopback device. Fixing the initialization order is a much bigger problem
with no obvious solution thus far.

The BUG is triggered when the loopback is set down and the netif_running
check added by a1a22c1206 fails. The fill_node descends to checking
rt->rt6i_idev for ignore_routes_with_linkdown and since rt6i_idev is
NULL it faults.

The null_entry route should not be processed in a dump request. Catch
and ignore. This check is done in rt6_dump_route as it is the highest
place in the callchain with knowledge of both the route and the network
namespace.

which is why I omit it.

The rt->rt6i_idev = in6_dev_get(loopback_dev) is apparently not correct,
at that time loopback_dev is just registered and not up or running, its
in6_dev pointer should be NULL, we need to listen to inet6addr event to
make it non-NULL. I thought you apparently knew this...

Re: [Patch net] ipv6: ignore null_entry in inet6_rtm_getroute() too

[David Ahern]

On 2/28/17 10:44 AM, Cong Wang wrote:
> Like commit 1f17e2f2c8a8 ("net: ipv6: ignore null_entry on route dumps"),
> we need to ignore null entry in inet6_rtm_getroute() too.
> 
> Return -ENOENT here because we return the same errno when deleting
> the null entry.
> 
> Fixes: a1a22c1206 ("net: ipv6: Keep nexthop of multipath route on admin down")
> Reported-by: Dmitry Vyukov 
> Cc: David Ahern 
> Signed-off-by: Cong Wang 
> ---
>  net/ipv6/route.c | 6 ++
>  1 file changed, 6 insertions(+)
> 
> diff --git a/net/ipv6/route.c b/net/ipv6/route.c
> index f54f426..25590d1 100644
> --- a/net/ipv6/route.c
> +++ b/net/ipv6/route.c
> @@ -3627,6 +3627,12 @@ static int inet6_rtm_getroute(struct sk_buff *in_skb, 
> struct nlmsghdr *nlh)
>   rt = (struct rt6_info *)ip6_route_output(net, NULL, );
>   }
>  
> + if (rt == net->ipv6.ip6_null_entry) {
> + ip6_rt_put(rt);
> + err = -ENOENT;
> + goto errout;
> + }
> +
>   skb = alloc_skb(NLMSG_GOODSIZE, GFP_KERNEL);
>   if (!skb) {
>   ip6_rt_put(rt);
> 

hold on. That test exposed something else, not just a getroute problem.
I accidentally ran 'unsahre -n; ip -6 ro ls' on my host machine instead
of a VM, so took some time to recover. dumproute already covers the null
route.

I'll get back to this in the afternoon.

[Patch net] ipv6: ignore null_entry in inet6_rtm_getroute() too

[Cong Wang]

Like commit 1f17e2f2c8a8 ("net: ipv6: ignore null_entry on route dumps"),
we need to ignore null entry in inet6_rtm_getroute() too.

Return -ENOENT here because we return the same errno when deleting
the null entry.

Fixes: a1a22c1206 ("net: ipv6: Keep nexthop of multipath route on admin down")
Reported-by: Dmitry Vyukov 
Cc: David Ahern 
Signed-off-by: Cong Wang 
---
 net/ipv6/route.c | 6 ++
 1 file changed, 6 insertions(+)

diff --git a/net/ipv6/route.c b/net/ipv6/route.c
index f54f426..25590d1 100644
--- a/net/ipv6/route.c
+++ b/net/ipv6/route.c
@@ -3627,6 +3627,12 @@ static int inet6_rtm_getroute(struct sk_buff *in_skb, 
struct nlmsghdr *nlh)
rt = (struct rt6_info *)ip6_route_output(net, NULL, );
}
 
+   if (rt == net->ipv6.ip6_null_entry) {
+   ip6_rt_put(rt);
+   err = -ENOENT;
+   goto errout;
+   }
+
skb = alloc_skb(NLMSG_GOODSIZE, GFP_KERNEL);
if (!skb) {
ip6_rt_put(rt);
-- 
2.5.5