netfilter: fix wrong arithmetics regarding NFT_REJECT_ICMPX_MAX

NFT_REJECT_ICMPX_MAX should be __NFT_REJECT_ICMPX_MAX - 1.

nft_reject_icmp_code() and nft_reject_icmpv6_code() are called from the
packet path, so BUG_ON in case we try to access an unknown abstracted
ICMP code. This should not happen since we already validate this from
nft_reject_{inet,bridge}_init().

Fixes: 51b0a5d ("netfilter: nft_reject: introduce icmp code abstraction for inet and bridge")
Reported-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>

include/uapi/linux/netfilter/nf_tables.h

@@ -774,7 +774,7 @@ enum nft_reject_inet_code {
 	NFT_REJECT_ICMPX_ADMIN_PROHIBITED,
 	__NFT_REJECT_ICMPX_MAX
 };
-#define NFT_REJECT_ICMPX_MAX	(__NFT_REJECT_ICMPX_MAX + 1)
+#define NFT_REJECT_ICMPX_MAX	(__NFT_REJECT_ICMPX_MAX - 1)
 
 /**
  * enum nft_reject_attributes - nf_tables reject expression netlink attributes

net/netfilter/nft_reject.c

@@ -72,7 +72,7 @@ int nft_reject_dump(struct sk_buff *skb, const struct nft_expr *expr)
 }
 EXPORT_SYMBOL_GPL(nft_reject_dump);
 
-static u8 icmp_code_v4[NFT_REJECT_ICMPX_MAX] = {
+static u8 icmp_code_v4[NFT_REJECT_ICMPX_MAX + 1] = {
 	[NFT_REJECT_ICMPX_NO_ROUTE]		= ICMP_NET_UNREACH,
 	[NFT_REJECT_ICMPX_PORT_UNREACH]		= ICMP_PORT_UNREACH,
 	[NFT_REJECT_ICMPX_HOST_UNREACH]		= ICMP_HOST_UNREACH,
@@ -81,16 +81,15 @@ static u8 icmp_code_v4[NFT_REJECT_ICMPX_MAX] = {
 
 int nft_reject_icmp_code(u8 code)
 {
-	if (code > NFT_REJECT_ICMPX_MAX)
-		return -EINVAL;
+	BUG_ON(code > NFT_REJECT_ICMPX_MAX);
 
 	return icmp_code_v4[code];
 }
 
 EXPORT_SYMBOL_GPL(nft_reject_icmp_code);
 
 
-static u8 icmp_code_v6[NFT_REJECT_ICMPX_MAX] = {
+static u8 icmp_code_v6[NFT_REJECT_ICMPX_MAX + 1] = {
 	[NFT_REJECT_ICMPX_NO_ROUTE]		= ICMPV6_NOROUTE,
 	[NFT_REJECT_ICMPX_PORT_UNREACH]		= ICMPV6_PORT_UNREACH,
 	[NFT_REJECT_ICMPX_HOST_UNREACH]		= ICMPV6_ADDR_UNREACH,
@@ -99,8 +98,7 @@ static u8 icmp_code_v6[NFT_REJECT_ICMPX_MAX] = {
 
 int nft_reject_icmpv6_code(u8 code)
 {
-	if (code > NFT_REJECT_ICMPX_MAX)
-		return -EINVAL;
+	BUG_ON(code > NFT_REJECT_ICMPX_MAX);
 
 	return icmp_code_v6[code];
 }