netdev - [PATCH net 7/8] netfilter: nf_queue: handle socket prefetch

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Message-Id: <20220301215337.378405-8-pablo@netfilter.org>
Date:   Tue,  1 Mar 2022 22:53:36 +0100
From:   Pablo Neira Ayuso <pablo@...filter.org>
To:     netfilter-devel@...r.kernel.org
Cc:     davem@...emloft.net, netdev@...r.kernel.org, kuba@...nel.org
Subject: [PATCH net 7/8] netfilter: nf_queue: handle socket prefetch

From: Florian Westphal <fw@...len.de>

In case someone combines bpf socket assign and nf_queue, then we will
queue an skb who references a struct sock that did not have its
reference count incremented.

As we leave rcu protection, there is no guarantee that skb->sk is still
valid.

For refcount-less skb->sk case, try to increment the reference count
and then override the destructor.

In case of failure we have two choices: orphan the skb and 'delete'
preselect or let nf_queue() drop the packet.

Do the latter, it should not happen during normal operation.

Fixes: cf7fbe660f2d ("bpf: Add socket assign support")
Acked-by: Joe Stringer <joe@...ium.io>
Signed-off-by: Florian Westphal <fw@...len.de>
---
 net/netfilter/nf_queue.c | 12 ++++++++++++
 1 file changed, 12 insertions(+)

diff --git a/net/netfilter/nf_queue.c b/net/netfilter/nf_queue.c
index e39549c55945..63d1516816b1 100644
--- a/net/netfilter/nf_queue.c
+++ b/net/netfilter/nf_queue.c
@@ -180,6 +180,18 @@ static int __nf_queue(struct sk_buff *skb, const struct nf_hook_state *state,
 		break;
 	}
 
+	if (skb_sk_is_prefetched(skb)) {
+		struct sock *sk = skb->sk;
+
+		if (!sk_is_refcounted(sk)) {
+			if (!refcount_inc_not_zero(&sk->sk_refcnt))
+				return -ENOTCONN;
+
+			/* drop refcount on skb_orphan */
+			skb->destructor = sock_edemux;
+		}
+	}
+
 	entry = kmalloc(sizeof(*entry) + route_key_size, GFP_ATOMIC);
 	if (!entry)
 		return -ENOMEM;
-- 
2.30.2