netfilter: nft_limit: do not ignore unsupported flags

Bail out if userspace provides unsupported flags, otherwise future
extensions to the limit expression will be silently ignored by the
kernel.

Fixes: c7862a5 ("netfilter: nft_limit: allow to invert matching criteria")
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>

Author: ummakynes

net/netfilter/nft_limit.c

@@ -58,6 +58,7 @@ static inline bool nft_limit_eval(struct nft_limit_priv *priv, u64 cost)
 static int nft_limit_init(struct nft_limit_priv *priv,
 			  const struct nlattr * const tb[], bool pkts)
 {
+	bool invert = false;
 	u64 unit, tokens;
 
 	if (tb[NFTA_LIMIT_RATE] == NULL ||
@@ -90,19 +91,23 @@ static int nft_limit_init(struct nft_limit_priv *priv,
 				 priv->rate);
 	}
 
+	if (tb[NFTA_LIMIT_FLAGS]) {
+		u32 flags = ntohl(nla_get_be32(tb[NFTA_LIMIT_FLAGS]));
+
+		if (flags & ~NFT_LIMIT_F_INV)
+			return -EOPNOTSUPP;
+
+		if (flags & NFT_LIMIT_F_INV)
+			invert = true;
+	}
+
 	priv->limit = kmalloc(sizeof(*priv->limit), GFP_KERNEL_ACCOUNT);
 	if (!priv->limit)
 		return -ENOMEM;
 
 	priv->limit->tokens = tokens;
 	priv->tokens_max = priv->limit->tokens;
-
-	if (tb[NFTA_LIMIT_FLAGS]) {
-		u32 flags = ntohl(nla_get_be32(tb[NFTA_LIMIT_FLAGS]));
-
-		if (flags & NFT_LIMIT_F_INV)
-			priv->invert = true;
-	}
+	priv->invert = invert;
 	priv->limit->last = ktime_get_ns();
 	spin_lock_init(&priv->limit->lock);