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From:   Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To:     linux-kernel@vger.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        stable@vger.kernel.org, Joe Stringer <joe@cilium.io>,
        Florian Westphal <fw@strlen.de>
Subject: [PATCH 5.10 045/105] netfilter: nf_queue: handle socket prefetch
Date:   Mon,  7 Mar 2022 10:18:48 +0100
Message-Id: <20220307091645.453234294@linuxfoundation.org>
In-Reply-To: <20220307091644.179885033@linuxfoundation.org>
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From: Florian Westphal <fw@strlen.de>

commit 3b836da4081fa585cf6c392f62557496f2cb0efe upstream.

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@cilium.io>
Signed-off-by: Florian Westphal <fw@strlen.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
 net/netfilter/nf_queue.c |   12 ++++++++++++
 1 file changed, 12 insertions(+)

--- a/net/netfilter/nf_queue.c
+++ b/net/netfilter/nf_queue.c
@@ -189,6 +189,18 @@ static int __nf_queue(struct sk_buff *sk
 		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;