netfilter: nft_limit: reject configurations that cause integer overflow

Reject bogus configs where internal token counter wraps around.
This only occurs with very very large requests, such as 17gbyte/s.

Its better to reject this rather than having incorrect ratelimit.

Fixes: d2168e8 ("netfilter: nft_limit: add per-byte limiting")
Signed-off-by: Florian Westphal <[email protected]>
Signed-off-by: Pablo Neira Ayuso <[email protected]>

net/netfilter/nft_limit.c

@@ -58,17 +58,19 @@ 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)
 {
+	u64 unit, tokens, rate_with_burst;
 	bool invert = false;
-	u64 unit, tokens;
 
 	if (tb[NFTA_LIMIT_RATE] == NULL ||
 	    tb[NFTA_LIMIT_UNIT] == NULL)
 		return -EINVAL;
 
 	priv->rate = be64_to_cpu(nla_get_be64(tb[NFTA_LIMIT_RATE]));
+	if (priv->rate == 0)
+		return -EINVAL;
+
 	unit = be64_to_cpu(nla_get_be64(tb[NFTA_LIMIT_UNIT]));
-	priv->nsecs = unit * NSEC_PER_SEC;
-	if (priv->rate == 0 || priv->nsecs < unit)
+	if (check_mul_overflow(unit, NSEC_PER_SEC, &priv->nsecs))
 		return -EOVERFLOW;
 
 	if (tb[NFTA_LIMIT_BURST])
@@ -77,18 +79,25 @@ static int nft_limit_init(struct nft_limit_priv *priv,
 	if (pkts && priv->burst == 0)
 		priv->burst = NFT_LIMIT_PKT_BURST_DEFAULT;
 
-	if (priv->rate + priv->burst < priv->rate)
+	if (check_add_overflow(priv->rate, priv->burst, &rate_with_burst))
 		return -EOVERFLOW;
 
 	if (pkts) {
-		tokens = div64_u64(priv->nsecs, priv->rate) * priv->burst;
+		u64 tmp = div64_u64(priv->nsecs, priv->rate);
+
+		if (check_mul_overflow(tmp, priv->burst, &tokens))
+			return -EOVERFLOW;
 	} else {
+		u64 tmp;
+
 		/* The token bucket size limits the number of tokens can be
 		 * accumulated. tokens_max specifies the bucket size.
 		 * tokens_max = unit * (rate + burst) / rate.
 		 */
-		tokens = div64_u64(priv->nsecs * (priv->rate + priv->burst),
-				 priv->rate);
+		if (check_mul_overflow(priv->nsecs, rate_with_burst, &tmp))
+			return -EOVERFLOW;
+
+		tokens = div64_u64(tmp, priv->rate);
 	}
 
 	if (tb[NFTA_LIMIT_FLAGS]) {