netfilter: nft_compat: fix handling of large matchinfo size

currently matchinfo gets stored in the expression, but some xt matches
are very large.

To handle those we either need to switch nft core to kvmalloc and increase
size limit, or allocate the info blob of large matches separately.

This does the latter, this limits the scope of the changes to
nft_compat.

I picked a threshold of 192, this allows most matches to work as before and
handle only few ones via separate alloation (cgroup, u32, sctp, rt).
Signed-off-by: NFlorian Westphal <fw@strlen.de>
Signed-off-by: NPablo Neira Ayuso <pablo@netfilter.org>

net/netfilter/nft_compat.c

@@ -36,6 +36,13 @@ struct nft_xt {
 	struct rcu_head		rcu_head;
 };
 
+/* Used for matches where *info is larger than X byte */
+#define NFT_MATCH_LARGE_THRESH	192
+
+struct nft_xt_match_priv {
+	void *info;
+};
+
 static bool nft_xt_put(struct nft_xt *xt)
 {
 	if (--xt->refcnt == 0) {
@@ -352,6 +359,15 @@ static void __nft_match_eval(const struct nft_expr *expr,
 	}
 }
 
+static void nft_match_large_eval(const struct nft_expr *expr,
+				 struct nft_regs *regs,
+				 const struct nft_pktinfo *pkt)
+{
+	struct nft_xt_match_priv *priv = nft_expr_priv(expr);
+
+	__nft_match_eval(expr, regs, pkt, priv->info);
+}
+
 static void nft_match_eval(const struct nft_expr *expr,
 			   struct nft_regs *regs,
 			   const struct nft_pktinfo *pkt)
@@ -458,6 +474,24 @@ nft_match_init(const struct nft_ctx *ctx, const struct nft_expr *expr,
 	return __nft_match_init(ctx, expr, tb, nft_expr_priv(expr));
 }
 
+static int
+nft_match_large_init(const struct nft_ctx *ctx, const struct nft_expr *expr,
+		     const struct nlattr * const tb[])
+{
+	struct nft_xt_match_priv *priv = nft_expr_priv(expr);
+	struct xt_match *m = expr->ops->data;
+	int ret;
+
+	priv->info = kmalloc(XT_ALIGN(m->matchsize), GFP_KERNEL);
+	if (!priv->info)
+		return -ENOMEM;
+
+	ret = __nft_match_init(ctx, expr, tb, priv->info);
+	if (ret)
+		kfree(priv->info);
+	return ret;
+}
+
 static void
 __nft_match_destroy(const struct nft_ctx *ctx, const struct nft_expr *expr,
 		    void *info)
@@ -482,6 +516,15 @@ nft_match_destroy(const struct nft_ctx *ctx, const struct nft_expr *expr)
 	__nft_match_destroy(ctx, expr, nft_expr_priv(expr));
 }
 
+static void
+nft_match_large_destroy(const struct nft_ctx *ctx, const struct nft_expr *expr)
+{
+	struct nft_xt_match_priv *priv = nft_expr_priv(expr);
+
+	__nft_match_destroy(ctx, expr, priv->info);
+	kfree(priv->info);
+}
+
 static int __nft_match_dump(struct sk_buff *skb, const struct nft_expr *expr,
 			    void *info)
 {
@@ -503,6 +546,13 @@ static int nft_match_dump(struct sk_buff *skb, const struct nft_expr *expr)
 	return __nft_match_dump(skb, expr, nft_expr_priv(expr));
 }
 
+static int nft_match_large_dump(struct sk_buff *skb, const struct nft_expr *e)
+{
+	struct nft_xt_match_priv *priv = nft_expr_priv(e);
+
+	return __nft_match_dump(skb, e, priv->info);
+}
+
 static int nft_match_validate(const struct nft_ctx *ctx,
 			      const struct nft_expr *expr,
 			      const struct nft_data **data)
@@ -670,6 +720,7 @@ nft_match_select_ops(const struct nft_ctx *ctx,
 {
 	struct nft_xt *nft_match;
 	struct xt_match *match;
+	unsigned int matchsize;
 	char *mt_name;
 	u32 rev, family;
 	int err;
@@ -709,7 +760,6 @@ nft_match_select_ops(const struct nft_ctx *ctx,
 
 	nft_match->refcnt = 0;
 	nft_match->ops.type = &nft_match_type;
-	nft_match->ops.size = NFT_EXPR_SIZE(XT_ALIGN(match->matchsize));
 	nft_match->ops.eval = nft_match_eval;
 	nft_match->ops.init = nft_match_init;
 	nft_match->ops.destroy = nft_match_destroy;
@@ -717,6 +767,18 @@ nft_match_select_ops(const struct nft_ctx *ctx,
 	nft_match->ops.validate = nft_match_validate;
 	nft_match->ops.data = match;
 
+	matchsize = NFT_EXPR_SIZE(XT_ALIGN(match->matchsize));
+	if (matchsize > NFT_MATCH_LARGE_THRESH) {
+		matchsize = NFT_EXPR_SIZE(sizeof(struct nft_xt_match_priv));
+
+		nft_match->ops.eval = nft_match_large_eval;
+		nft_match->ops.init = nft_match_large_init;
+		nft_match->ops.destroy = nft_match_large_destroy;
+		nft_match->ops.dump = nft_match_large_dump;
+	}
+
+	nft_match->ops.size = matchsize;
+
 	list_add(&nft_match->head, &nft_match_list);
 
 	return &nft_match->ops;