linux-kernel - Re: [PATCH] Advertise PPPoE MTU / avoid memory leak.

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Message-Id: <20060923.145600.51855973.davem@davemloft.net>
Date:	Sat, 23 Sep 2006 14:56:00 -0700 (PDT)
From:	David Miller <davem@...emloft.net>
To:	mostrows@...thlink.net
Cc:	linux-kernel@...r.kernel.org, netdev@...r.kernel.org,
	ppp-bugs@...samba.org
Subject: Re: [PATCH] Advertise PPPoE MTU / avoid memory leak.

From: mostrows@...thlink.net
Date: Sat, 23 Sep 2006 12:30:23 -0500

> __pppoe_xmit must free any skb it allocates if there is an error
> submitting the skb downstream.

This isn't right, dev_queue_xmit() can return -ENETDOWN and still
free the SKB, so your change will cause the SKB to be freed up
twice in that case, from dev_queue_xmit():

	rc = -ENETDOWN;
	rcu_read_unlock_bh();

out_kfree_skb:
	kfree_skb(skb);
	return rc;

dev_queue_xmit() is basically expected to consume the packet,
error or not.

What case of calling dev_queue_xmit() did you discover that did not
kfree the SKB on error?  We should fix that.  On a quick scan on the
entire dev_queue_xmit() implmentation, I cannot find such a case.
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