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

From: Michal Ostrowski
Date: Sun Sep 24 2006 - 08:31:07 EST

On Sat, 2006-09-23 at 14:56 -0700, David Miller wrote:
> From: mostrows@xxxxxxxxxxxxx
> 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.

I think the call path via dev->hard_start_xmit, if it fails, may result
in an skb not being freed. This appears to be the case with the e100.c
driver. The qdisc_restart path to dev->hard_start_xmit also appears
susceptible to this. It appears that not all devices agree as to who
should clean-up an skb on error.

Michal Ostrowski <mostrows@xxxxxxxxxxxxx>

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