zebra: disallow resolution to duplicate nexthops

Disallow the resolution to nexthops that are marked duplicate.
When we are resolving to an ecmp group, it's possible this
group has duplicates.

I found this when I hit a bug where we can have groups resolving
to each other and cause the resolved->next->next pointer to increase
exponentially. Sufficiently large ecmp and zebra will grind to a hault.

Like so:

```
D>  4.4.4.14/32 [150/0] via 1.1.1.1 (recursive), weight 1, 00:00:02
  *                       via 1.1.1.1, dummy1 onlink, weight 1, 00:00:02
                        via 4.4.4.1 (recursive), weight 1, 00:00:02
                          via 1.1.1.1, dummy1, weight 1, 00:00:02
                        via 4.4.4.2 (recursive), weight 1, 00:00:02
                          via 1.1.1.1, dummy1, weight 1, 00:00:02
                        via 4.4.4.3 (recursive), weight 1, 00:00:02
                          via 1.1.1.1, dummy1, weight 1, 00:00:02
                        via 4.4.4.4 (recursive), weight 1, 00:00:02
                          via 1.1.1.1, dummy1, weight 1, 00:00:02
                        via 4.4.4.5 (recursive), weight 1, 00:00:02
                          via 1.1.1.1, dummy1, weight 1, 00:00:02
                        via 4.4.4.6 (recursive), weight 1, 00:00:02
                          via 1.1.1.1, dummy1, weight 1, 00:00:02
                        via 4.4.4.7 (recursive), weight 1, 00:00:02
                          via 1.1.1.1, dummy1, weight 1, 00:00:02
                        via 4.4.4.8 (recursive), weight 1, 00:00:02
                          via 1.1.1.1, dummy1, weight 1, 00:00:02
                        via 4.4.4.9 (recursive), weight 1, 00:00:02
                          via 1.1.1.1, dummy1, weight 1, 00:00:02
                        via 4.4.4.10 (recursive), weight 1, 00:00:02
                          via 1.1.1.1, dummy1, weight 1, 00:00:02
                        via 4.4.4.11 (recursive), weight 1, 00:00:02
                          via 1.1.1.1, dummy1, weight 1, 00:00:02
                        via 4.4.4.12 (recursive), weight 1, 00:00:02
                          via 1.1.1.1, dummy1, weight 1, 00:00:02
                        via 4.4.4.13 (recursive), weight 1, 00:00:02
                          via 1.1.1.1, dummy1, weight 1, 00:00:02
                        via 4.4.4.15 (recursive), weight 1, 00:00:02
                          via 1.1.1.1, dummy1 onlink, weight 1, 00:00:02
                          via 1.1.1.1, dummy1, weight 1, 00:00:02
                          via 1.1.1.1, dummy1, weight 1, 00:00:02
                          via 1.1.1.1, dummy1, weight 1, 00:00:02
                          via 1.1.1.1, dummy1, weight 1, 00:00:02
                          via 1.1.1.1, dummy1, weight 1, 00:00:02
                          via 1.1.1.1, dummy1, weight 1, 00:00:02
                          via 1.1.1.1, dummy1, weight 1, 00:00:02
                          via 1.1.1.1, dummy1, weight 1, 00:00:02
                          via 1.1.1.1, dummy1, weight 1, 00:00:02
                          via 1.1.1.1, dummy1, weight 1, 00:00:02
                          via 1.1.1.1, dummy1, weight 1, 00:00:02
                          via 1.1.1.1, dummy1, weight 1, 00:00:02
                          via 1.1.1.1, dummy1, weight 1, 00:00:02
                          via 1.1.1.1, dummy1, weight 1, 00:00:02
                          via 1.1.1.1, dummy1 onlink, weight 1, 00:00:02
                          via 1.1.1.1, dummy1, weight 1, 00:00:02
                          via 1.1.1.1, dummy1, weight 1, 00:00:02
                          via 1.1.1.1, dummy1, weight 1, 00:00:02
                          via 1.1.1.1, dummy1, weight 1, 00:00:02
                          via 1.1.1.1, dummy1, weight 1, 00:00:02
                          via 1.1.1.1, dummy1, weight 1, 00:00:02
                          via 1.1.1.1, dummy1, weight 1, 00:00:02
                          via 1.1.1.1, dummy1, weight 1, 00:00:02
                          via 1.1.1.1, dummy1, weight 1, 00:00:02
                          via 1.1.1.1, dummy1, weight 1, 00:00:02
                          via 1.1.1.1, dummy1, weight 1, 00:00:02
                          via 1.1.1.1, dummy1, weight 1, 00:00:02
                          via 1.1.1.1, dummy1, weight 1, 00:00:02
                          via 1.1.1.1, dummy1, weight 1, 00:00:02
                          via 1.1.1.1, dummy1, weight 1, 00:00:02
                        via 4.4.4.16 (recursive), weight 1, 00:00:02
                          via 1.1.1.1, dummy1 onlink, weight 1, 00:00:02
                          via 1.1.1.1, dummy1, weight 1, 00:00:02
                          via 1.1.1.1, dummy1, weight 1, 00:00:02
                          via 1.1.1.1, dummy1, weight 1, 00:00:02
                          via 1.1.1.1, dummy1, weight 1, 00:00:02
                          via 1.1.1.1, dummy1, weight 1, 00:00:02
                          via 1.1.1.1, dummy1, weight 1, 00:00:02
                          via 1.1.1.1, dummy1, weight 1, 00:00:02
                          via 1.1.1.1, dummy1, weight 1, 00:00:02
                          via 1.1.1.1, dummy1, weight 1, 00:00:02
                          via 1.1.1.1, dummy1, weight 1, 00:00:02
                          via 1.1.1.1, dummy1, weight 1, 00:00:02
                          via 1.1.1.1, dummy1, weight 1, 00:00:02
                          via 1.1.1.1, dummy1, weight 1, 00:00:02
                          via 1.1.1.1, dummy1, weight 1, 00:00:02
                          via 1.1.1.1, dummy1, weight 1, 00:00:02
D>  4.4.4.15/32 [150/0] via 1.1.1.1 (recursive), weight 1, 00:00:09
  *                       via 1.1.1.1, dummy1 onlink, weight 1, 00:00:09
                        via 4.4.4.1 (recursive), weight 1, 00:00:09
                          via 1.1.1.1, dummy1, weight 1, 00:00:09
                        via 4.4.4.2 (recursive), weight 1, 00:00:09
                          via 1.1.1.1, dummy1, weight 1, 00:00:09
                        via 4.4.4.3 (recursive), weight 1, 00:00:09
                          via 1.1.1.1, dummy1, weight 1, 00:00:09
                        via 4.4.4.4 (recursive), weight 1, 00:00:09
                          via 1.1.1.1, dummy1, weight 1, 00:00:09
                        via 4.4.4.5 (recursive), weight 1, 00:00:09
                          via 1.1.1.1, dummy1, weight 1, 00:00:09
                        via 4.4.4.6 (recursive), weight 1, 00:00:09
                          via 1.1.1.1, dummy1, weight 1, 00:00:09
                        via 4.4.4.7 (recursive), weight 1, 00:00:09
                          via 1.1.1.1, dummy1, weight 1, 00:00:09
                        via 4.4.4.8 (recursive), weight 1, 00:00:09
                          via 1.1.1.1, dummy1, weight 1, 00:00:09
                        via 4.4.4.9 (recursive), weight 1, 00:00:09
                          via 1.1.1.1, dummy1, weight 1, 00:00:09
                        via 4.4.4.10 (recursive), weight 1, 00:00:09
                          via 1.1.1.1, dummy1, weight 1, 00:00:09
                        via 4.4.4.11 (recursive), weight 1, 00:00:09
                          via 1.1.1.1, dummy1, weight 1, 00:00:09
                        via 4.4.4.12 (recursive), weight 1, 00:00:09
                          via 1.1.1.1, dummy1, weight 1, 00:00:09
                        via 4.4.4.13 (recursive), weight 1, 00:00:09
                          via 1.1.1.1, dummy1, weight 1, 00:00:09
                        via 4.4.4.14 (recursive), weight 1, 00:00:09
                          via 1.1.1.1, dummy1, weight 1, 00:00:09
                        via 4.4.4.16 (recursive), weight 1, 00:00:09
                          via 1.1.1.1, dummy1 onlink, weight 1, 00:00:09
                          via 1.1.1.1, dummy1, weight 1, 00:00:09
                          via 1.1.1.1, dummy1, weight 1, 00:00:09
                          via 1.1.1.1, dummy1, weight 1, 00:00:09
                          via 1.1.1.1, dummy1, weight 1, 00:00:09
                          via 1.1.1.1, dummy1, weight 1, 00:00:09
                          via 1.1.1.1, dummy1, weight 1, 00:00:09
                          via 1.1.1.1, dummy1, weight 1, 00:00:09
                          via 1.1.1.1, dummy1, weight 1, 00:00:09
                          via 1.1.1.1, dummy1, weight 1, 00:00:09
                          via 1.1.1.1, dummy1, weight 1, 00:00:09
                          via 1.1.1.1, dummy1, weight 1, 00:00:09
                          via 1.1.1.1, dummy1, weight 1, 00:00:09
                          via 1.1.1.1, dummy1, weight 1, 00:00:09
                          via 1.1.1.1, dummy1, weight 1, 00:00:09
                          via 1.1.1.1, dummy1, weight 1, 00:00:09
D>  4.4.4.16/32 [150/0] via 1.1.1.1 (recursive), weight 1, 00:00:19
  *                       via 1.1.1.1, dummy1 onlink, weight 1, 00:00:19
                        via 4.4.4.1 (recursive), weight 1, 00:00:19
                          via 1.1.1.1, dummy1, weight 1, 00:00:19
                        via 4.4.4.2 (recursive), weight 1, 00:00:19

...............
................

and on...

```

You can repro the above via:

```
kernel routes:

1.1.1.1 dev dummy1 scope link

4.4.4.0/24 via 1.1.1.1 dev dummy1

==============================

config:

nexthop-group doof
 nexthop 1.1.1.1
 nexthop 4.4.4.1
 nexthop 4.4.4.10
 nexthop 4.4.4.11
 nexthop 4.4.4.12
 nexthop 4.4.4.13
 nexthop 4.4.4.14
 nexthop 4.4.4.15
 nexthop 4.4.4.16
 nexthop 4.4.4.2
 nexthop 4.4.4.3
 nexthop 4.4.4.4
 nexthop 4.4.4.5
 nexthop 4.4.4.6
 nexthop 4.4.4.7
 nexthop 4.4.4.8
 nexthop 4.4.4.9
!

===========================

Then use sharpd to install 4.4.4.16 -> 4.4.4.1 pointing to that nexthop
group in decending order.
```

With these changes it prevents the growing ecmp above by disallowing
duplicates to be in the resolution decision. These nexthops are not
installed anyways so why should we be resolving to them?

Signed-off-by: Stephen Worley <sworley@nvidia.com>

diff --git a/zebra/zebra_nhg.c b/zebra/zebra_nhg.c
index 3d92124b8d4cc4eae3b6ee6c857e4ad88c538eb4..cfc31eeca604e29b76df4653c681e6d9b1b736a4 100644 (file)
--- a/zebra/zebra_nhg.c
+++ b/zebra/zebra_nhg.c
@@ -1754,6 +1754,10 @@ static bool nexthop_valid_resolve(const struct nexthop *nexthop,
        if (!CHECK_FLAG(resolved->flags, NEXTHOP_FLAG_ACTIVE))
                return false;
 
+       /* Must not be duplicate */
+       if (CHECK_FLAG(resolved->flags, NEXTHOP_FLAG_DUPLICATE))
+               return false;
+
        switch (nexthop->type) {
        case NEXTHOP_TYPE_IPV4_IFINDEX:
        case NEXTHOP_TYPE_IPV6_IFINDEX: