netfilter: nft_tproxy: restrict to prerouting hook

TPROXY is only allowed from prerouting, but nft_tproxy doesn't check this.
This fixes a crash (null dereference) when using tproxy from e.g. output.

Fixes: 4ed8eb6570a4 ("netfilter: nf_tables: Add native tproxy support")
Reported-by: Shell Chen <xierch@gmail.com>
Signed-off-by: Florian Westphal <fw@strlen.de>

diff --git a/net/netfilter/nft_tproxy.c b/net/netfilter/nft_tproxy.c
index 68b2eed..62da25a 100644 (file)
--- a/net/netfilter/nft_tproxy.c
+++ b/net/netfilter/nft_tproxy.c
@@ -312,6 +312,13 @@ static int nft_tproxy_dump(struct sk_buff *skb,
        return 0;
 }
 
+static int nft_tproxy_validate(const struct nft_ctx *ctx,
+                              const struct nft_expr *expr,
+                              const struct nft_data **data)
+{
+       return nft_chain_validate_hooks(ctx->chain, 1 << NF_INET_PRE_ROUTING);
+}
+
 static struct nft_expr_type nft_tproxy_type;
 static const struct nft_expr_ops nft_tproxy_ops = {
        .type           = &nft_tproxy_type,
@@ -321,6 +328,7 @@ static const struct nft_expr_ops nft_tproxy_ops = {
        .destroy        = nft_tproxy_destroy,
        .dump           = nft_tproxy_dump,
        .reduce         = NFT_REDUCE_READONLY,
+       .validate       = nft_tproxy_validate,
 };
 
 static struct nft_expr_type nft_tproxy_type __read_mostly = {