netfilter: nf_tables: remove useless U8_MAX validation

After call nft_data_init, size is already validated and desc.len will
not exceed the sizeof(struct nft_data), i.e. 16 bytes. So it will never
exceed U8_MAX.

Furthermore, in nft_immediate_init, we forget to call nft_data_uninit
when desc.len exceeds U8_MAX, although this will not happen, but it's
a logical mistake.

Now remove these redundant validation introduced by commit 36b701fae12a
("netfilter: nf_tables: validate maximum value of u32 netlink attributes")

Signed-off-by: Liping Zhang <zlpnobody@gmail.com>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>

net/netfilter/nft_cmp.c

@@ -84,9 +84,6 @@ static int nft_cmp_init(const struct nft_ctx *ctx, const struct nft_expr *expr,
 	if (err < 0)
 		return err;
 
-	if (desc.len > U8_MAX)
-		return -ERANGE;
-
 	priv->op  = ntohl(nla_get_be32(tb[NFTA_CMP_OP]));
 	priv->len = desc.len;
 	return 0;

net/netfilter/nft_immediate.c

@@ -54,9 +54,6 @@ static int nft_immediate_init(const struct nft_ctx *ctx,
 	if (err < 0)
 		return err;
 
-	if (desc.len > U8_MAX)
-		return -ERANGE;
-
 	priv->dlen = desc.len;
 
 	priv->dreg = nft_parse_register(tb[NFTA_IMMEDIATE_DREG]);