Subject: Re: [PATCH] ipv4: add a fib_type to fib_info

From: Chris Clayton <[email-masked]>
Date: Thu, 04 Oct 2012 14:08:31 +0100

On 10/04/12 12:25, Eric Dumazet wrote:
> On Tue, 2012-10-02 at 17:48 +0200, Eric Dumazet wrote:
>> From: Eric Dumazet <[email-masked]>
>>
>> On Tue, 2012-10-02 at 17:35 +0200, Eric Dumazet wrote:
>>> On Mon, 2012-10-01 at 22:04 +0200, Eric Dumazet wrote:
>>>> On Mon, 2012-10-01 at 16:01 -0400, David Miller wrote:
>>>
>>>>> If you can find a way to more reliably trigger the case, that would
>>>>> help us immensely.
>>>>
>>>> I am building a KMEMCHECK kernel, as a last try before my night ;)
>>>
>>> This was a total disaster. KMEMCHECK dies horribly on my machine
>>>
>>> David, shouldnt we use a nh_rth_forward instead of a nh_rth_input in
>>> __mkroute_input() ?
>>>
>>> (And change rt_cache_route() as well ?)
>>>
>>> I am testing a patch right now.
>>
>
> OK so I implemented David idea and it seems to work.
>
> Testers are needed, thanks ! ;)
>

I've tested 3.6.0 with this patch applied and networking in a WinXP KVM 
client is now working fine. The patch applies cleanly to 3.6.0, so I 
assume the patch will be forwarded to stable in due course.

Tested-by: Chris Clayton <[email-masked]>

> [PATCH] ipv4: add a fib_type to fib_info
>
> commit d2d68ba9fe8 (ipv4: Cache input routes in fib_info nexthops.)
> introduced a regression for forwarding.
>
> This was hard to reproduce but the symptom was that packets were
> delivered to local host instead of being forwarded.
>
> David suggested to add fib_type to fib_info so that we dont
> inadvertently share same fib_info for different purposes.
>
> With help from Julian Anastasov who provided very helpful
> hints, reproduced here :
>
> <quote>
>          Can it be a problem related to fib_info reuse
> from different routes. For example, when local IP address
> is created for subnet we have:
>
> broadcast 192.168.0.255 dev DEV  proto kernel  scope link  src
> 192.168.0.1
> 192.168.0.0/24 dev DEV  proto kernel  scope link  src 192.168.0.1
> local 192.168.0.1 dev DEV  proto kernel  scope host  src 192.168.0.1
>
>          The "dev DEV  proto kernel  scope link  src 192.168.0.1" is
> a reused fib_info structure where we put cached routes.
> The result can be same fib_info for 192.168.0.255 and
> 192.168.0.0/24. RTN_BROADCAST is cached only for input
> routes. Incoming broadcast to 192.168.0.255 can be cached
> and can cause problems for traffic forwarded to 192.168.0.0/24.
> So, this patch should solve the problem because it
> separates the broadcast from unicast traffic.
>
>          And the ip_route_input_slow caching will work for
> local and broadcast input routes (above routes 1 and 3) just
> because they differ in scope and use different fib_info.
>
> </quote>
>
> Many thanks to Chris Clayton for his patience and help.
>
> Reported-by: Chris Clayton <[email-masked]>
> Bisected-by: Chris Clayton <[email-masked]>
> Reported-by: Dave Jones <[email-masked]>
> Signed-off-by: Eric Dumazet <[email-masked]>
> Cc: Julian Anastasov <[email-masked]>
> ---
>   include/net/ip_fib.h     |    1 +
>   net/ipv4/fib_semantics.c |    2 ++
>   2 files changed, 3 insertions(+)
>
> diff --git a/include/net/ip_fib.h b/include/net/ip_fib.h
> index 926142e..9497be1 100644
> --- a/include/net/ip_fib.h
> +++ b/include/net/ip_fib.h
> @@ -102,6 +102,7 @@ struct fib_info {
>   	unsigned char		fib_dead;
>   	unsigned char		fib_protocol;
>   	unsigned char		fib_scope;
> +	unsigned char		fib_type;
>   	__be32			fib_prefsrc;
>   	u32			fib_priority;
>   	u32			*fib_metrics;
> diff --git a/net/ipv4/fib_semantics.c b/net/ipv4/fib_semantics.c
> index 3509065..2677530 100644
> --- a/net/ipv4/fib_semantics.c
> +++ b/net/ipv4/fib_semantics.c
> @@ -314,6 +314,7 @@ static struct fib_info *fib_find_info(const struct fib_info *nfi)
>   		    nfi->fib_scope == fi->fib_scope &&
>   		    nfi->fib_prefsrc == fi->fib_prefsrc &&
>   		    nfi->fib_priority == fi->fib_priority &&
> +		    nfi->fib_type == fi->fib_type &&
>   		    memcmp(nfi->fib_metrics, fi->fib_metrics,
>   			   sizeof(u32) * RTAX_MAX) == 0 &&
>   		    ((nfi->fib_flags ^ fi->fib_flags) & ~RTNH_F_DEAD) == 0 &&
> @@ -833,6 +834,7 @@ struct fib_info *fib_create_info(struct fib_config *cfg)
>   	fi->fib_flags = cfg->fc_flags;
>   	fi->fib_priority = cfg->fc_priority;
>   	fi->fib_prefsrc = cfg->fc_prefsrc;
> +	fi->fib_type = cfg->fc_type;
>
>   	fi->fib_nhs = nhs;
>   	change_nexthops(fi) {
>
>