[PATCH] netfilter: ipset: Fix serious failure in CIDR tracking

[Oliver <oliver@8.c.9.b.0.7.4.0.1.0.0.2.ip6.arpa>]

From: Oliver Smith <oliver@8.c.9.b.0.7.4.0.1.0.0.2.ip6.arpa>

This fixes a serious bug affecting all hash types with a net element -
specifically, if a CIDR value is deleted such that none of the same size
exist any more, all larger (less-specific) values will then fail to
match. Adding back any prefix with a CIDR equal to or more specific than
the one deleted will fix it.

Steps to reproduce:
ipset -N test hash:net
ipset -A test 1.1.0.0/16
ipset -A test 2.2.2.0/24
ipset -T test 1.1.1.1		#1.1.1.1 IS in set
ipset -D test 2.2.2.0/24
ipset -T test 1.1.1.1		#1.1.1.1 IS NOT in set

This is due to the fact that the nets counter was unconditionally
decremented prior to the iteration that shifts up the entries. Now, we
first check if there is a proceeding entry and if not, decrement it and
return. Otherwise, we proceed to iterate and then clean up the last
element afterwards.

Signed-off-by: Oliver Smith <oliver@8.c.9.b.0.7.4.0.1.0.0.2.ip6.arpa>
---
 kernel/net/netfilter/ipset/ip_set_hash_gen.h | 8 +++++---
 1 file changed, 5 insertions(+), 3 deletions(-)

diff --git a/kernel/net/netfilter/ipset/ip_set_hash_gen.h b/kernel/net/netfilter/ipset/ip_set_hash_gen.h
index 7a5b776..f0f0c8d 100644
--- a/kernel/net/netfilter/ipset/ip_set_hash_gen.h
+++ b/kernel/net/netfilter/ipset/ip_set_hash_gen.h
@@ -311,15 +311,17 @@ mtype_del_cidr(struct htype *h, u8 cidr, u8 nets_length, u8 n)
 
 	for (i = 0; i < nets_length - 1 && h->nets[i].cidr[n] != cidr; i++)
 		;
-	h->nets[i].nets[n]--;
-
-	if (h->nets[i].nets[n] != 0)
+	if (h->nets[i+1].nets[n] == 0) {
+		h->nets[i].nets[n]--;
 		return;
+	}
 
 	for (j = i; j < nets_length - 1 && h->nets[j].nets[n]; j++) {
 		h->nets[j].cidr[n] = h->nets[j + 1].cidr[n];
 		h->nets[j].nets[n] = h->nets[j + 1].nets[n];
 	}
+	h->nets[j].cidr[n] = 0;
+	h->nets[j].nets[n] = 0;
 }
 #endif
 
-- 
1.8.3.2