udp: ipv4: must add synchronization in udp_sk_rx_dst_set() (97502231) · Commits · 戴 / test

Unlike TCP, UDP input path does not hold the socket lock. Before messing with sk->sk_rx_dst, we must use a spinlock, otherwise multiple cpus could leak a refcount. This patch also takes care of renewing a stale dst entry. (When the sk->sk_rx_dst would not be used by IP early demux) Fixes: ("udp: ipv4: Add udp early demux") Signed-off-by:

Eric Dumazet <edumazet@google.com> Cc: Shawn Bohrer <sbohrer@rgmadvisors.com> Signed-off-by:

David S. Miller <davem@davemloft.net>

net/ipv4/udp.c

+16 −6

Original line number	Diff line number	Diff line
		@@ -1599,12 +1599,21 @@ static void flush_stack(struct sock **stack, unsigned int count,
		kfree_skb(skb1);
		}

		static void udp_sk_rx_dst_set(struct sock sk, const struct sk_buff skb)
		/* For TCP sockets, sk_rx_dst is protected by socket lock
		* For UDP, we use sk_dst_lock to guard against concurrent changes.
		*/
		static void udp_sk_rx_dst_set(struct sock sk, struct dst_entry dst)
		{
		struct dst_entry *dst = skb_dst(skb);
		struct dst_entry *old;

		spin_lock(&sk->sk_dst_lock);
		old = sk->sk_rx_dst;
		if (likely(old != dst)) {
		dst_hold(dst);
		sk->sk_rx_dst = dst;
		dst_release(old);
		}
		spin_unlock(&sk->sk_dst_lock);
		}

		/*
		@@ -1737,10 +1746,11 @@ int __udp4_lib_rcv(struct sk_buff skb, struct udp_table udptable,

		sk = skb_steal_sock(skb);
		if (sk) {
		struct dst_entry *dst = skb_dst(skb);
		int ret;

		if (unlikely(sk->sk_rx_dst == NULL))
		udp_sk_rx_dst_set(sk, skb);
		if (unlikely(sk->sk_rx_dst != dst))
		udp_sk_rx_dst_set(sk, dst);

		ret = udp_queue_rcv_skb(sk, skb);
		sock_put(sk);

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