netfilter: ipset: Out of bound access in hash:net* types fixed

Dave Jones reported that KASan detected out of bounds access in hash:net*
types:

[   23.139532] ==================================================================
[   23.146130] BUG: KASan: out of bounds access in hash_net4_add_cidr+0x1db/0x220 at addr ffff8800d4844b58
[   23.152937] Write of size 4 by task ipset/457
[   23.159742] =============================================================================
[   23.166672] BUG kmalloc-512 (Not tainted): kasan: bad access detected
[   23.173641] -----------------------------------------------------------------------------
[   23.194668] INFO: Allocated in hash_net_create+0x16a/0x470 age=7 cpu=1 pid=456
[   23.201836]  __slab_alloc.constprop.66+0x554/0x620
[   23.208994]  __kmalloc+0x2f2/0x360
[   23.216105]  hash_net_create+0x16a/0x470
[   23.223238]  ip_set_create+0x3e6/0x740
[   23.230343]  nfnetlink_rcv_msg+0x599/0x640
[   23.237454]  netlink_rcv_skb+0x14f/0x190
[   23.244533]  nfnetlink_rcv+0x3f6/0x790
[   23.251579]  netlink_unicast+0x272/0x390
[   23.258573]  netlink_sendmsg+0x5a1/0xa50
[   23.265485]  SYSC_sendto+0x1da/0x2c0
[   23.272364]  SyS_sendto+0xe/0x10
[   23.279168]  entry_SYSCALL_64_fastpath+0x12/0x6f

The bug is fixed in the patch and the testsuite is extended in ipset
to check cidr handling more thoroughly.
Signed-off-by: Jozsef Kadlecsik <kadlec@blackhole.kfki.hu>

net/netfilter/ipset/ip_set_hash_gen.h

@@ -152,9 +152,13 @@ htable_bits(u32 hashsize)
 #define SET_HOST_MASK(family)	(family == AF_INET ? 32 : 128)
 
 #ifdef IP_SET_HASH_WITH_NET0
+/* cidr from 0 to SET_HOST_MASK() value and c = cidr + 1 */
 #define NLEN(family)		(SET_HOST_MASK(family) + 1)
+#define CIDR_POS(c)		((c) - 1)
 #else
+/* cidr from 1 to SET_HOST_MASK() value and c = cidr + 1 */
 #define NLEN(family)		SET_HOST_MASK(family)
+#define CIDR_POS(c)		((c) - 2)
 #endif
 
 #else
@@ -305,7 +309,7 @@ mtype_add_cidr(struct htype *h, u8 cidr, u8 nets_length, u8 n)
 		} else if (h->nets[i].cidr[n] < cidr) {
 			j = i;
 		} else if (h->nets[i].cidr[n] == cidr) {
-			h->nets[cidr - 1].nets[n]++;
+			h->nets[CIDR_POS(cidr)].nets[n]++;
 			return;
 		}
 	}
@@ -314,7 +318,7 @@ mtype_add_cidr(struct htype *h, u8 cidr, u8 nets_length, u8 n)
 			h->nets[i].cidr[n] = h->nets[i - 1].cidr[n];
 	}
 	h->nets[i].cidr[n] = cidr;
-	h->nets[cidr - 1].nets[n] = 1;
+	h->nets[CIDR_POS(cidr)].nets[n] = 1;
 }
 
 static void
@@ -325,8 +329,8 @@ mtype_del_cidr(struct htype *h, u8 cidr, u8 nets_length, u8 n)
 	for (i = 0; i < nets_length; i++) {
 		if (h->nets[i].cidr[n] != cidr)
 			continue;
-		h->nets[cidr - 1].nets[n]--;
-		if (h->nets[cidr - 1].nets[n] > 0)
+		h->nets[CIDR_POS(cidr)].nets[n]--;
+		if (h->nets[CIDR_POS(cidr)].nets[n] > 0)
 			return;
 		for (j = i; j < net_end && h->nets[j].cidr[n]; j++)
 			h->nets[j].cidr[n] = h->nets[j + 1].cidr[n];