[PATCH] ipv4: add a fib_type to fib_info

Eric Dumazet
2012-10-04T11:25:32Z

On Tue, 2012-10-02 at 17:48 +0200, Eric Dumazet wrote:
> From: Eric Dumazet <edumazet@google.com>
>
> 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 ! ;)

[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 <chris2553@googlemail.com>
Bisected-by: Chris Clayton <chris2553@googlemail.com>
Reported-by: Dave Jones <davej@redhat.com>
Signed-off-by: Eric Dumazet <edumazet@google.com>
Cc: Julian Anastasov <ja@ssi.bg>
---
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) {