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Commit 97502231 authored by Eric Dumazet's avatar Eric Dumazet Committed by David S. Miller
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udp: ipv4: must add synchronization in udp_sk_rx_dst_set() 



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: 421b3885 ("udp: ipv4: Add udp early demux")
Signed-off-by: default avatarEric Dumazet <edumazet@google.com>
Cc: Shawn Bohrer <sbohrer@rgmadvisors.com>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parent a1bf1750

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);