netdev - Re: [PATCH] openvswitch: fix a use after free

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Message-ID: <1413468747.28798.19.camel@edumazet-glaptop2.roam.corp.google.com>
Date:	Thu, 16 Oct 2014 07:12:27 -0700
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	roy.qing.li@...il.com
Cc:	netdev@...r.kernel.org, Jesse Gross <jesse@...ira.com>,
	Andy Zhou <azhou@...ira.com>,
	Pravin B Shelar <pshelar@...ira.com>
Subject: Re: [PATCH] openvswitch: fix a use after free

On Thu, 2014-10-16 at 17:01 +0800, roy.qing.li@...il.com wrote:
> From: Li RongQing <roy.qing.li@...il.com>
> 
> pskb_may_pull() called by arphdr_ok can change skb->data, so put the arp
> setting after arphdr_ok to avoid the use the freed memory
> 
> Signed-off-by: Li RongQing <roy.qing.li@...il.com>
> ---
>  net/openvswitch/flow.c |    3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/net/openvswitch/flow.c b/net/openvswitch/flow.c
> index 62db02b..b13ba5e 100644
> --- a/net/openvswitch/flow.c
> +++ b/net/openvswitch/flow.c
> @@ -557,10 +557,11 @@ static int key_extract(struct sk_buff *skb, struct sw_flow_key *key)
>  	} else if (key->eth.type == htons(ETH_P_ARP) ||
>  		   key->eth.type == htons(ETH_P_RARP)) {
>  		struct arp_eth_header *arp;
> +		bool arp_t = arphdr_ok(skb);

This is a strange name for a bool.  _t suffix is normally used by
typedef.

>  
>  		arp = (struct arp_eth_header *)skb_network_header(skb);
>  
> -		if (arphdr_ok(skb) &&
> +		if (arp_t &&
>  		    arp->ar_hrd == htons(ARPHRD_ETHER) &&
>  		    arp->ar_pro == htons(ETH_P_IP) &&
>  		    arp->ar_hln == ETH_ALEN &&

Fixes: 0714812134d7d ("openvswitch: Eliminate memset() from flow_extract.")

By doing this bug hunting, you also can CC bug author so that he knows
what happened. Maybe he will avoid similar mistakes in the future.



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