[PATCH 5.15,5.10,5.4,4.19] netfilter: nft_tproxy: restrict to prerouting hook

[Qingfang DENG <dqfext@gmail.com>]

From: Florian Westphal <fw@strlen.de>

commit 18bbc3213383a82b05383827f4b1b882e3f0a5a5 upstream.

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>
Signed-off-by: Qingfang DENG <dqfext@gmail.com>
---
 net/netfilter/nft_tproxy.c | 8 ++++++++
 1 file changed, 8 insertions(+)

--- a/net/netfilter/nft_tproxy.c
+++ b/net/netfilter/nft_tproxy.c
@@ -312,6 +312,13 @@ static int nft_tproxy_dump(struct sk_buf
 	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,
@@ -320,6 +327,7 @@ static const struct nft_expr_ops nft_tpr
 	.init		= nft_tproxy_init,
 	.destroy	= nft_tproxy_destroy,
 	.dump		= nft_tproxy_dump,
+	.validate	= nft_tproxy_validate,
 };
 
 static struct nft_expr_type nft_tproxy_type __read_mostly = {