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Commit f6ba8d33 authored by Eric Dumazet's avatar Eric Dumazet Committed by David S. Miller
Browse files

netem: fix skb_orphan_partial() 

I should have known that lowering skb->truesize was dangerous :/

In case packets are not leaving the host via a standard Ethernet device,
but looped back to local sockets, bad things can happen, as reported
by Michael Madsen ( https://bugzilla.kernel.org/show_bug.cgi?id=195713

 )

So instead of tweaking skb->truesize, lets change skb->destructor
and keep a reference on the owner socket via its sk_refcnt.

Fixes: f2f872f9 ("netem: Introduce skb_orphan_partial() helper")
Signed-off-by: default avatarEric Dumazet <edumazet@google.com>
Reported-by: default avatarMichael Madsen <mkm@nabto.com>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parent 4e3c60ed

net/core/sock.c

+8 −12
Original line number Diff line number Diff line
@@ -1803,28 +1803,24 @@ EXPORT_SYMBOL(skb_set_owner_w); 
 * delay queue. We want to allow the owner socket to send more

 * packets, as if they were already TX completed by a typical driver.

 * But we also want to keep skb->sk set because some packet schedulers

 * rely on it (sch_fq for example). So we set skb->truesize to a small

 * amount (1) and decrease sk_wmem_alloc accordingly.

 * rely on it (sch_fq for example).

 */

void skb_orphan_partial(struct sk_buff *skb)

{

	/* If this skb is a TCP pure ACK or already went here,

	 * we have nothing to do. 2 is already a very small truesize.

	 */

	if (skb->truesize <= 2)

	if (skb_is_tcp_pure_ack(skb))

		return;



	/* TCP stack sets skb->ooo_okay based on sk_wmem_alloc,

	 * so we do not completely orphan skb, but transfert all

	 * accounted bytes but one, to avoid unexpected reorders.

	 */

	if (skb->destructor == sock_wfree

#ifdef CONFIG_INET

	    || skb->destructor == tcp_wfree

#endif

		) {

		atomic_sub(skb->truesize - 1, &skb->sk->sk_wmem_alloc);

		skb->truesize = 1;

		struct sock *sk = skb->sk;



		if (atomic_inc_not_zero(&sk->sk_refcnt)) {

			atomic_sub(skb->truesize, &sk->sk_wmem_alloc);

			skb->destructor = sock_efree;

		}

	} else {

		skb_orphan(skb);

	}