linux-kernel - Re: [PATCH] xfrm: init skb_head lock for transport-mode packets

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Message-ID: <20180104112026.436rgqaeokcden4r@shodan.usersys.redhat.com>
Date:   Thu, 4 Jan 2018 12:20:26 +0100
From:   Artem Savkov <asavkov@...hat.com>
To:     Herbert Xu <herbert@...dor.apana.org.au>
Cc:     Steffen Klassert <steffen.klassert@...unet.com>,
        netdev@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] xfrm: init skb_head lock for transport-mode packets

On Thu, Jan 04, 2018 at 10:01:32PM +1100, Herbert Xu wrote:
> On Thu, Jan 04, 2018 at 11:36:28AM +0100, Artem Savkov wrote:
> > Commit acf568ee859f "xfrm: Reinject transport-mode packets through tasklet"
> > adds an sk_buff_head queue, but never initializes trans->queue.lock, which
> > results in a "spinlock bad magic" BUG on skb_queue_tail() call in
> > xfrm_trans_queue.
> > Use skb_queue_head_init() instead of __skb_queue_head_init() to properly
> > initialize said lock.
> > 
> > Signed-off-by: Artem Savkov <asavkov@...hat.com>
> 
> Thanks for catching this.  But we don't need the lock as this
> is meant to be per-CPU only.  So we should remove the locking
> instead:

Right, thats a better solution.

Reported-and-tested-by: Artem Savkov <asavkov@...hat.com>

Thank you.

> ---8<---
> xfrm: Use __skb_queue_tail in xfrm_trans_queue
> 
> We do not need locking in xfrm_trans_queue because it is designed
> to use per-CPU buffers.  However, the original code incorrectly
> used skb_queue_tail which takes the lock.  This patch switches
> it to __skb_queue_tail instead.
> 
> Reported-by: Artem Savkov <asavkov@...hat.com>
> Fixes: acf568ee859f ("xfrm: Reinject transport-mode packets...")
> Signed-off-by: Herbert Xu <herbert@...dor.apana.org.au>
> 
> diff --git a/net/xfrm/xfrm_input.c b/net/xfrm/xfrm_input.c
> index 098f47a..1eb0bba 100644
> --- a/net/xfrm/xfrm_input.c
> +++ b/net/xfrm/xfrm_input.c
> @@ -511,7 +511,7 @@ int xfrm_trans_queue_net(struct net *net, struct sk_buff *skb,
>  
>  	XFRM_TRANS_SKB_CB(skb)->finish = finish;
>  	XFRM_TRANS_SKB_CB(skb)->net = net;
> -	skb_queue_tail(&trans->queue, skb);
> +	__skb_queue_tail(&trans->queue, skb);
>  	tasklet_schedule(&trans->tasklet);
>  	return 0;
>  }

-- 
Regards,
  Artem