netdev - Re: [PATCH net] phonet: properly unshare skbs in phonet

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Message-ID: <ba49c1524db476eab37647078cfeddcc@roundcube.remlab.net>
Date:	Wed, 13 Jan 2016 14:26:33 +0200
From:	Rémi Denis-Courmont <remi@...lab.net>
To:	Eric Dumazet <eric.dumazet@...il.com>
Cc:	Network Development <netdev@...r.kernel.org>
Subject: Re: [PATCH net] phonet: properly unshare skbs in
 phonet_rcv()

Le 2016-01-12 18:58, Eric Dumazet a écrit :
> From: Eric Dumazet <edumazet@...gle.com>
>
> Ivaylo Dimitrov reported a regression caused by commit 7866a621043f
> ("dev: add per net_device packet type chains").
>
> skb->dev becomes NULL and we crash in __netif_receive_skb_core().
>
> Before above commit, different kind of bugs or corruptions could 
> happen
> without major crash.

Hmm... was that always a problem then, or did it get introduced 
earlier? I thought it was impossible for skb to be shared on PF-recv 
callback way back.

> But the root cause is that phonet_rcv() can queue skb without 
> checking
> if skb is shared or not.
>
> Many thanks to Ivaylo Dimitrov for his help, diagnosis and tests.
>
> Reported-by: Ivaylo Dimitrov <ivo.g.dimitrov.75@...il.com>
> Tested-by: Ivaylo Dimitrov <ivo.g.dimitrov.75@...il.com>
> Signed-off-by: Eric Dumazet <edumazet@...gle.com>
> Cc: Remi Denis-Courmont <courmisch@...il.com>
> ---
>  net/phonet/af_phonet.c |    4 ++++
>  1 file changed, 4 insertions(+)
>
> diff --git a/net/phonet/af_phonet.c b/net/phonet/af_phonet.c
> index 10d42f3220ab..f925753668a7 100644
> --- a/net/phonet/af_phonet.c
> +++ b/net/phonet/af_phonet.c
> @@ -377,6 +377,10 @@ static int phonet_rcv(struct sk_buff *skb,
> struct net_device *dev,
>  	struct sockaddr_pn sa;
>  	u16 len;
>
> +	skb = skb_share_check(skb, GFP_ATOMIC);
> +	if (!skb)
> +		return NET_RX_DROP;
> +
>  	/* check we have at least a full Phonet header */
>  	if (!pskb_pull(skb, sizeof(struct phonethdr)))
>  		goto out;

Ack, thanks.

-- 
Rémi Denis-Courmont
http://www.remlab.net/