Commit 3b836da4 authored Mar 01, 2022 by Florian Westphal

netfilter: nf_queue: handle socket prefetch



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: cf7fbe66 ("bpf: Add socket assign support")
Acked-by: Joe Stringer <joe@cilium.io>
Signed-off-by: Florian Westphal <fw@strlen.de>

parent c3873070

net/netfilter/nf_queue.c

+12 −0

Original line number	Diff line number	Diff line
		@@ -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;