[PATCH v2 nf] netfilter: nft_socket: only do sk lookups when indev is available

[PATCH v2 nf] netfilter: nft_socket: only do sk lookups when indev is available

[Florian Westphal]

Check if the incoming interface is available and NFT_BREAK
in case neither skb->sk nor input device are set.

Because nf_sk_lookup_slow*() assume packet headers are in the
'in' direction, use in postrouting is not going to yield a meaningful
result.  Same is true for the forward chain, so restrict the use
to prerouting, input and output.

Use in output work if a socket is already attached to the skb.

Reported-by: Topi Miettinen <toiwoton@gmail.com>
Fixes: 554ced0a6e29 ("netfilter: nf_tables: add support for native socket matching")
Signed-off-by: Florian Westphal <fw@strlen.de>
---
 v2: add .validate, very similar to Pablos patch, but also permit OUTPUT
     chain, no other changes.

 net/netfilter/nft_socket.c | 51 +++++++++++++++++++++++++++-----------
 1 file changed, 37 insertions(+), 14 deletions(-)

diff --git a/net/netfilter/nft_socket.c b/net/netfilter/nft_socket.c
index 6d9e8e0a3a7d..a33557d7f350 100644
--- a/net/netfilter/nft_socket.c
+++ b/net/netfilter/nft_socket.c
@@ -54,6 +54,32 @@ nft_sock_get_eval_cgroupv2(u32 *dest, struct sock *sk, const struct nft_pktinfo
 }
 #endif
 
+static struct sock *nft_socket_do_lookup(const struct nft_pktinfo *pkt)
+{
+	const struct net_device *indev = nft_in(pkt);
+	const struct sk_buff *skb = pkt->skb;
+	struct sock *sk = NULL;
+
+	if (!indev)
+		return NULL;
+
+	switch (nft_pf(pkt)) {
+	case NFPROTO_IPV4:
+		sk = nf_sk_lookup_slow_v4(nft_net(pkt), skb, indev);
+		break;
+#if IS_ENABLED(CONFIG_NF_TABLES_IPV6)
+	case NFPROTO_IPV6:
+		sk = nf_sk_lookup_slow_v6(nft_net(pkt), skb, indev);
+		break;
+#endif
+	default:
+		WARN_ON_ONCE(1);
+		break;
+	}
+
+	return sk;
+}
+
 static void nft_socket_eval(const struct nft_expr *expr,
 			    struct nft_regs *regs,
 			    const struct nft_pktinfo *pkt)
@@ -67,20 +93,7 @@ static void nft_socket_eval(const struct nft_expr *expr,
 		sk = NULL;
 
 	if (!sk)
-		switch(nft_pf(pkt)) {
-		case NFPROTO_IPV4:
-			sk = nf_sk_lookup_slow_v4(nft_net(pkt), skb, nft_in(pkt));
-			break;
-#if IS_ENABLED(CONFIG_NF_TABLES_IPV6)
-		case NFPROTO_IPV6:
-			sk = nf_sk_lookup_slow_v6(nft_net(pkt), skb, nft_in(pkt));
-			break;
-#endif
-		default:
-			WARN_ON_ONCE(1);
-			regs->verdict.code = NFT_BREAK;
-			return;
-		}
+		sk = nft_socket_do_lookup(pkt);
 
 	if (!sk) {
 		regs->verdict.code = NFT_BREAK;
@@ -224,6 +237,15 @@ static bool nft_socket_reduce(struct nft_regs_track *track,
 	return nft_expr_reduce_bitwise(track, expr);
 }
 
+static int nft_socket_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) |
+					(1 << NF_INET_LOCAL_IN) |
+					(1 << NF_INET_LOCAL_OUT));
+}
+
 static struct nft_expr_type nft_socket_type;
 static const struct nft_expr_ops nft_socket_ops = {
 	.type		= &nft_socket_type,
@@ -231,6 +253,7 @@ static const struct nft_expr_ops nft_socket_ops = {
 	.eval		= nft_socket_eval,
 	.init		= nft_socket_init,
 	.dump		= nft_socket_dump,
+	.validate	= nft_socket_validate,
 	.reduce		= nft_socket_reduce,
 };
 
-- 
2.35.1

Re: [PATCH v2 nf] netfilter: nft_socket: only do sk lookups when indev is available

[Pablo Neira Ayuso]

On Thu, Apr 28, 2022 at 09:39:21AM +0200, Florian Westphal wrote:
> Check if the incoming interface is available and NFT_BREAK
> in case neither skb->sk nor input device are set.
> 
> Because nf_sk_lookup_slow*() assume packet headers are in the
> 'in' direction, use in postrouting is not going to yield a meaningful
> result.  Same is true for the forward chain, so restrict the use
> to prerouting, input and output.
> 
> Use in output work if a socket is already attached to the skb.

Applied to nf.git, thanks