netdev - Re: regression: tethering fails in 3.5 with iwlwifi

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Date:	Thu, 20 Sep 2012 14:45:01 +0200
From:	Eric Dumazet <edumazet@...gle.com>
To:	Johannes Berg <johannes@...solutions.net>
Cc:	artem.bityutskiy@...ux.intel.com, linux-wireless@...r.kernel.org,
	netdev <netdev@...r.kernel.org>
Subject: Re: regression: tethering fails in 3.5 with iwlwifi

I guess you only need to make sure 14 bytes of ethernet header are
available before eth_type_trans(skb, dev);

diff --git a/net/mac80211/rx.c b/net/mac80211/rx.c
index 61c621e..ffe5f84 100644
--- a/net/mac80211/rx.c
+++ b/net/mac80211/rx.c
@@ -1795,9 +1795,13 @@ ieee80211_deliver_skb(struct ieee80211_rx_data *rx)

                if (skb) {
                        /* deliver to local stack */
-                       skb->protocol = eth_type_trans(skb, dev);
-                       memset(skb->cb, 0, sizeof(skb->cb));
-                       netif_receive_skb(skb);
+                       if (pskb_may_pull(skb, sizeof(struct ethhdr))) {
+                               skb->protocol = eth_type_trans(skb, dev);
+                               memset(skb->cb, 0, sizeof(skb->cb));
+                               netif_receive_skb(skb);
+                       } else {
+                               kfree_skb(skb);
+                       }
                }
        }


On Thu, Sep 20, 2012 at 2:40 PM, Eric Dumazet <edumazet@...gle.com> wrote:
> OK, but which netif_receive_skb(), as I count 5 occurrences in
> net/mac80211/rx.c ?
>
> Instead of skb_linearize() calls
>
> you could try several values of XXX in
>
> pskb_may_pull(skb, XXX)
>
> So that you make sure XXX bytes are available in skb->head, and not
> the whole frame.
>
> One you know the limit for XXX, it might give a clue where a
> pskb_may_pull(skb, XXX) is missing.
>
> On Thu, Sep 20, 2012 at 2:35 PM, Johannes Berg
> <johannes@...solutions.net> wrote:
>> Hi,
>>
>>> >             56138f5 iwlwifi: dont pull too much payload in skb head
>>> >             3edaf3e mac80211: manage AP netdev carrier state
>>>
>>> The second patch (AP carrier state) actually exposed a connman issue
>>> which I fixed and submitted a connman patch:
>>> http://lists.connman.net/pipermail/connman/2012-September/011232.html
>>>
>>> However, Eric's patch still causes tethering problems to me.
>>
>>
>> Let me recap a bit. Artem is using connman, which sets up the wifi
>> interface as part of a bridge. It runs wpa_supplicant to create an AP
>> (only AP and mesh mode interfaces can be bridged anyway).
>>
>>
>> Eric, you said:
>>
>>> I would say some part of the stack assumes a header (I dont know wich
>>> one ?) is pulled in skb->head/data, and thats a bug.
>>>
>>> Always use pskb_may_pull(skb, XXX) to make sure you can access XXX
>>> bytes in skb->data
>>
>> I thought we'd figure out which part of the stack assumes a header, so I
>> asked Artem to test a one-line patch which adds "skb_linearize()" before
>> "netif_receive_skb()" in mac80211. This makes it work, but I'm not sure
>> where after that the bad assumption might be.
>>
>> johannes
>>
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