Re: [PATCH wpan 1/2] net: 6lowpan: fix reserved space for single frames

From: David Palma <david.palma@ntnu.no>
To: Stefan Schmidt <stefan@datenfreihafen.org>,
	Alexander Aring <aring@mojatatu.com>,
	stefan@osg.samsung.com
Cc: linux-wpan@vger.kernel.org, netdev@vger.kernel.org,
	kernel@mojatatu.com,
	Rabi Narayan Sahoo <rabinarayans0828@gmail.com>
Subject: Re: [PATCH wpan 1/2] net: 6lowpan: fix reserved space for single frames
Date: Fri, 6 Jul 2018 09:54:51 +0200	[thread overview]
Message-ID: <781a24ed-3783-abbf-7726-f377fd5eabca@ntnu.no> (raw)
In-Reply-To: <a2cb217f-7e22-e603-bd46-13d8764fee64@datenfreihafen.org>

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Hi Stefan,

On 05/07/18 13:16, Stefan Schmidt wrote:
> Hello.
> 
> [CC David Palma and Rabi Narayan Sahoo]
> 
> On 02.07.2018 22:32, Alexander Aring wrote:
>> This patch fixes patch add handling to take care tail and headroom for
>> single 6lowpan frames. We need to be sure we have a skb with the right
>> head and tailroom for single frames. This patch do it by using
>> skb_copy_expand() if head and tailroom is not enough allocated by upper
>> layer.
>>
>> Bugzilla: https://bugzilla.kernel.org/show_bug.cgi?id=195059
>> Reported-by: David Palma <david.palma@ntnu.no>
>> Reported-by: Rabi Narayan Sahoo <rabinarayans0828@gmail.com>
>> Signed-off-by: Alexander Aring <aring@mojatatu.com>
> 
> David, Rabi and you please test these two patches and verify that it
> fixes the problems you have?
> 
> regards
> Stefan Schmidt
> 

The patches fix the problems!

I've tested them against different packet sizes and no kernel panic.

The patches were applied in Debian's 4.9.88-1+deb9u1 x86_64 kernel,
which before the patches showed the reported issue.

Thanks again to Alex for looking into it.

Cheers,
-- 
David

>> ---
>>  net/ieee802154/6lowpan/tx.c | 21 ++++++++++++++++++---
>>  1 file changed, 18 insertions(+), 3 deletions(-)
>>
>> diff --git a/net/ieee802154/6lowpan/tx.c b/net/ieee802154/6lowpan/tx.c
>> index e6ff5128e61a..d0c4d220de08 100644
>> --- a/net/ieee802154/6lowpan/tx.c
>> +++ b/net/ieee802154/6lowpan/tx.c
>> @@ -265,9 +265,24 @@ netdev_tx_t lowpan_xmit(struct sk_buff *skb, struct net_device *ldev)
>>  	/* We must take a copy of the skb before we modify/replace the ipv6
>>  	 * header as the header could be used elsewhere
>>  	 */
>> -	skb = skb_unshare(skb, GFP_ATOMIC);
>> -	if (!skb)
>> -		return NET_XMIT_DROP;
>> +	if (unlikely(skb_headroom(skb) < ldev->needed_headroom ||
>> +		     skb_tailroom(skb) < ldev->needed_tailroom)) {
>> +		struct sk_buff *nskb;
>> +
>> +		nskb = skb_copy_expand(skb, ldev->needed_headroom,
>> +				       ldev->needed_tailroom, GFP_ATOMIC);
>> +		if (likely(skb)) {
>> +			consume_skb(skb);
>> +			skb = nskb;
>> +		} else {
>> +			kfree_skb(skb);
>> +			return NET_XMIT_DROP;
>> +		}
>> +	} else {
>> +		skb = skb_unshare(skb, GFP_ATOMIC);
>> +		if (!skb)
>> +			return NET_XMIT_DROP;
>> +	}
>>  
>>  	ret = lowpan_header(skb, ldev, &dgram_size, &dgram_offset);
>>  	if (ret < 0) {
>>

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